improve examples

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LICENSE-APACHE

@@ -0,0 +1,201 @@
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LICENSE-MIT

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2024 Turtle Graphics Library Contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -195,7 +195,32 @@ Add the `svg` feature to enable SVG export functionality:
 cargo run --example export_svg --features svg
 ```
 
-### Usage
+### Command-Line SVG Export
+
+When using the `turtle_main` macro with the `svg` feature enabled, you can export drawings directly to SVG files using the `--export-svg` command-line parameter:
+
+```bash
+# Export any example to SVG without showing the window
+cargo run --example macro_demo --features svg -- --export-svg output.svg
+
+# Works with all turtle_main-based examples
+cargo run --example hello_turtle --features svg -- --export-svg square.svg
+```
+
+This will:
+- Execute all drawing commands instantly (no animation)
+- Export the result to an SVG file
+- Exit immediately without opening a window
+
+**Note**: The program still requires a display context to initialize. In headless environments, use `xvfb-run`:
+
+```bash
+xvfb-run -a cargo run --example macro_demo --features svg -- --export-svg output.svg
+```
+
+### Programmatic SVG Export
+
+You can also export SVG programmatically from your code:
 
 ```rust
 use turtle_lib::*;
@@ -239,6 +264,10 @@ cargo run --example nikolaus
 # SVG export example (requires --features svg)
 cargo run --example export_svg --features svg
 
+# Export any example to SVG using CLI parameter (requires --features svg)
+cargo run --example macro_demo --features svg -- --export-svg output.svg
+cargo run --example hello_turtle --features svg -- --export-svg square.svg
+
 # Logging example - shows how to enable debug output
 cargo run --example logging_example
 RUST_LOG=turtle_lib=debug cargo run --example logging_example

turtle-lib-macros/src/lib.rs

@@ -16,6 +16,14 @@ use syn::{parse_macro_input, ItemFn};
 /// - Creates a turtle instance (`turtle`)
 /// - Sets up the `TurtleApp` with your drawing commands
 /// - Provides a main loop with rendering and quit handling (ESC or Q)
+/// - Adds command-line parameter support for SVG export (when `svg` feature is enabled)
+///
+/// # Command-Line Parameters
+///
+/// When the `svg` feature is enabled, the following command-line parameter is available:
+///
+/// * `--export-svg <filename>` - Exports the drawing to an SVG file and exits immediately
+///   without opening the window. Example: `cargo run --features svg -- --export-svg output.svg`
 ///
 /// # Example
 ///
@@ -45,6 +53,13 @@ use syn::{parse_macro_input, ItemFn};
 /// }
 /// ```
 ///
+/// # SVG Export Example
+///
+/// ```bash
+/// # Run with SVG export (requires svg feature)
+/// cargo run --package turtle-lib --example macro_demo --features svg -- --export-svg output.svg
+/// ```
+///
 /// This expands to approximately:
 ///
 /// ```ignore
@@ -53,6 +68,10 @@ use syn::{parse_macro_input, ItemFn};
 ///
 /// #[macroquad::main("My Turtle Drawing")]
 /// async fn main() {
+///     // Parse CLI args for --export-svg flag
+///     let args: Vec<String> = std::env::args().collect();
+///     // ... (argument parsing logic)
+///     
 ///     let mut turtle = create_turtle_plan();
 ///     
 ///     // Your drawing code here
@@ -63,6 +82,8 @@ use syn::{parse_macro_input, ItemFn};
 ///
 ///     let mut app = TurtleApp::new().with_commands(turtle.build());
 ///
+///     // If --export-svg flag is present, export and exit
+///     // Otherwise, enter normal rendering loop
 ///     loop {
 ///         clear_background(WHITE);
 ///         app.update();
@@ -97,15 +118,29 @@ pub fn turtle_main(args: TokenStream, input: TokenStream) -> TokenStream {
     // Check if the function has the expected signature
     let has_turtle_param = input_fn.sig.inputs.len() == 1;
 
+    // Note: The following code has some duplication between the two branches
+    // (with/without turtle parameter). This is intentional in proc macros as
+    // we're generating different code paths, and extracting the common parts
+    // into helper functions would make the macro more complex without significant benefit.
+
     let expanded = if has_turtle_param {
         // Function takes a turtle parameter
         quote! {
             #[macroquad::main(#window_title)]
             async fn main() {
+                // Build function reused for both export and normal rendering
+                let mut build_commands = |turtle: &mut turtle_lib::TurtlePlan| {
+                    #fn_name(turtle);
+                };
+
+                // Handle optional SVG export internally in turtle-lib
+                turtle_lib::export::handle_svg_export(&mut build_commands);
+
+                // Normal rendering mode (with window)
                 let mut turtle = turtle_lib::create_turtle_plan();
 
                 // Call the user's function with the turtle
-                #fn_name(&mut turtle);
+                build_commands(&mut turtle);
 
                 let mut app = turtle_lib::TurtleApp::new()
                     .with_commands(turtle.build());
@@ -139,10 +174,18 @@ pub fn turtle_main(args: TokenStream, input: TokenStream) -> TokenStream {
         quote! {
             #[macroquad::main(#window_title)]
             async fn main() {
-                let mut turtle = turtle_lib::create_turtle_plan();
+                // Build function reused for both export and normal rendering
-
+                let mut build_commands = |turtle: &mut turtle_lib::TurtlePlan| {
-                // Inline the user's code
+                    let turtle = turtle;
                     #fn_block
+                };
+
+                // Handle optional SVG export internally in turtle-lib
+                turtle_lib::export::handle_svg_export(&mut build_commands);
+
+                // Normal rendering mode (with window)
+                let mut turtle = turtle_lib::create_turtle_plan();
+                build_commands(&mut turtle);
 
                 let mut app = turtle_lib::TurtleApp::new()
                     .with_commands(turtle.build());

turtle-lib/examples/cartesian_axes.rs

@@ -80,10 +80,10 @@ fn draw(turtle: &mut TurtlePlan) {
 
     // Draw and label 4 points (one per quadrant)
     let points = vec![
-        (vec2(120.0, 100.0), "A(2|1)"),
+        (vec2(100.0, 50.0), "A(2|1)"),
-        (vec2(-120.0, 100.0), "B(-2|1)"),
+        (vec2(-100.0, 50.0), "B(-2|1)"),
-        (vec2(-120.0, -100.0), "C(-2|-1)"),
+        (vec2(-100.0, -50.0), "C(-2|-1)"),
-        (vec2(120.0, -100.0), "D(2|-1)"),
+        (vec2(100.0, -50.0), "D(2|-1)"),
     ];
 
     for (position, label) in points {

turtle-lib/examples/export_svg.rs

@@ -1,5 +1,6 @@
 //! Beispiel: Exportiere ein SVG aus einer einfachen Zeichnung
 
+#[cfg(feature = "svg")]
 use turtle_lib::*;
 
 #[cfg(feature = "svg")]

turtle-lib/examples/koch.rs

@@ -20,7 +20,7 @@ fn koch(depth: u32, turtle: &mut TurtlePlan, distance: f32) {
 #[turtle_main("Koch Snowflake")]
 fn draw(turtle: &mut TurtlePlan) {
     // Position turtle
-    turtle.set_speed(1001);
+    turtle.set_speed(5000);
     turtle.pen_up();
     turtle.backward(150.0);
 
@@ -28,7 +28,7 @@ fn draw(turtle: &mut TurtlePlan) {
 
     // Draw Koch snowflake (triangle of Koch curves)
     for _ in 0..3 {
-        koch(4, turtle, 300.0);
+        koch(6, turtle, 300.0);
         turtle.right(120.0);
         turtle.set_speed(1200);
     }

turtle-lib/examples/test_svg_export.rs

@@ -0,0 +1,36 @@
+//! Test example for CLI SVG export feature
+//!
+//! Run this with: cargo run --package turtle-lib --example test_svg_export --features svg -- --export-svg test_output.svg
+
+use turtle_lib::*;
+
+#[turtle_main("SVG Export Test")]
+fn draw_test(turtle: &mut TurtlePlan) {
+    turtle.set_pen_color(RED);
+    turtle.set_pen_width(3.0);
+    
+    // Draw a square
+    for _ in 0..4 {
+        turtle.forward(100.0);
+        turtle.right(90.0);
+    }
+    
+    // Draw a circle
+    turtle.set_pen_color(BLUE);
+    turtle.pen_up();
+    turtle.forward(150.0);
+    turtle.pen_down();
+    turtle.circle_left(50.0, 360.0, 36);
+    
+    // Draw a filled triangle
+    turtle.set_fill_color(GREEN);
+    turtle.pen_up();
+    turtle.go_to(vec2(-50.0, 100.0));
+    turtle.pen_down();
+    turtle.begin_fill();
+    for _ in 0..3 {
+        turtle.forward(80.0);
+        turtle.right(120.0);
+    }
+    turtle.end_fill();
+}

turtle-lib/examples/yinyang.rs

@@ -23,5 +23,6 @@ fn draw(turtle: &mut TurtlePlan) {
         .left(90.0)
         .pen_down()
         .circle_right(8.0, 360.0, 12)
-        .end_fill();
+        .end_fill()
+        .hide();
 }

turtle-lib/src/builders.rs

@@ -1,7 +1,7 @@
 //! Builder pattern traits for creating turtle command sequences
 
 use crate::commands::{CommandQueue, TurtleCommand};
-use crate::general::{AnimationSpeed, Color, Coordinate, FontSize, Precision};
+use crate::general::{AnimationSpeed, Color, Coordinate, Degrees, FontSize, Precision};
 use crate::shapes::{ShapeType, TurtleShape};
 
 /// Trait for adding commands to a queue
@@ -91,10 +91,10 @@ pub trait Turnable: WithCommands {
     /// ```
     fn left<T>(&mut self, angle: T) -> &mut Self
     where
-        T: Into<Precision>,
+        T: Into<Degrees>,
     {
-        let degrees: Precision = angle.into();
+        self.get_commands_mut()
-        self.get_commands_mut().push(TurtleCommand::Turn(-degrees));
+            .push(TurtleCommand::Turn(-angle.into()));
         self
     }
 
@@ -118,10 +118,10 @@ pub trait Turnable: WithCommands {
     /// ```
     fn right<T>(&mut self, angle: T) -> &mut Self
     where
-        T: Into<Precision>,
+        T: Into<Degrees>,
     {
-        let degrees: Precision = angle.into();
+        self.get_commands_mut()
-        self.get_commands_mut().push(TurtleCommand::Turn(degrees));
+            .push(TurtleCommand::Turn(angle.into()));
         self
     }
 }
@@ -160,13 +160,12 @@ pub trait CurvedMovement: WithCommands {
     fn circle_left<R, A>(&mut self, radius: R, angle: A, steps: usize) -> &mut Self
     where
         R: Into<Precision>,
-        A: Into<Precision>,
+        A: Into<Degrees>,
     {
         let r: Precision = radius.into();
-        let a: Precision = angle.into();
         self.get_commands_mut().push(TurtleCommand::Circle {
             radius: r,
-            angle: a,
+            angle: angle.into(),
             steps,
             direction: crate::circle_geometry::CircleDirection::Left,
         });
@@ -207,13 +206,12 @@ pub trait CurvedMovement: WithCommands {
     fn circle_right<R, A>(&mut self, radius: R, angle: A, steps: usize) -> &mut Self
     where
         R: Into<Precision>,
-        A: Into<Precision>,
+        A: Into<Degrees>,
     {
         let r: Precision = radius.into();
-        let a: Precision = angle.into();
         self.get_commands_mut().push(TurtleCommand::Circle {
             radius: r,
-            angle: a,
+            angle: angle.into(),
             steps,
             direction: crate::circle_geometry::CircleDirection::Right,
         });
@@ -367,9 +365,9 @@ impl TurtlePlan {
     ///           .forward(100.0);
     /// }
     /// ```
-    pub fn set_heading(&mut self, heading: Precision) -> &mut Self {
+    pub fn set_heading<T: Into<Degrees>>(&mut self, heading: T) -> &mut Self {
         self.queue
-            .push(TurtleCommand::SetHeading(-heading.to_radians()));
+            .push(TurtleCommand::SetHeading(-heading.into().as_radians()));
         self
     }
 

turtle-lib/src/circle_geometry.rs

@@ -1,7 +1,43 @@
 //! Circle geometry calculations - single source of truth for `circle_left` and `circle_right`
 
+use crate::general::Radians;
 use macroquad::prelude::*;
 
+/// Generate evenly-spaced points along a circular arc.
+///
+/// Returns exactly `steps` points, uniformly distributed from (not including)
+/// the arc start to (including) the arc end.  This is the **single source of
+/// truth** for arc sampling used by tessellation, tween stroke drawing, and
+/// fill-polygon preview.
+///
+/// # Arguments
+/// * `center`      — centre of the circle
+/// * `radius`      — arc radius
+/// * `start_angle` — angle from `center` to the turtle's start position (radians)
+/// * `sweep_angle` — total arc sweep in radians (absolute; sign comes from `direction`)
+/// * `steps`       — number of sample points (clamped to ≥ 1)
+/// * `direction`   — which way the arc curves
+pub(crate) fn arc_points(
+    center: Vec2,
+    radius: f32,
+    start_angle: f32,
+    sweep_angle: f32,
+    steps: usize,
+    direction: CircleDirection,
+) -> Vec<Vec2> {
+    let n = steps.max(1);
+    let step_size = sweep_angle / n as f32;
+    (1..=n)
+        .map(|i| {
+            let a = match direction {
+                CircleDirection::Left => start_angle - step_size * i as f32,
+                CircleDirection::Right => start_angle + step_size * i as f32,
+            };
+            Vec2::new(center.x + radius * a.cos(), center.y + radius * a.sin())
+        })
+        .collect()
+}
+
 /// Direction of circular motion (in screen coordinates with Y-down)
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum CircleDirection {
@@ -10,11 +46,11 @@ pub enum CircleDirection {
 }
 
 /// Encapsulates all geometry for a circular arc
-pub struct CircleGeometry {
+pub(crate) struct CircleGeometry {
-    pub center: Vec2,
+    pub(crate) center: Vec2,
-    pub radius: f32,
+    pub(crate) radius: f32,
-    pub start_angle_from_center: f32, // radians
+    pub(crate) start_angle_from_center: f32, // radians
-    pub direction: CircleDirection,
+    pub(crate) direction: CircleDirection,
 }
 
 impl CircleGeometry {
@@ -22,12 +58,15 @@ impl CircleGeometry {
     #[must_use]
     pub fn new(
         turtle_pos: Vec2,
-        turtle_heading: f32,
+        turtle_heading: Radians,
         radius: f32,
         direction: CircleDirection,
     ) -> Self {
         use std::f32::consts::FRAC_PI_2;
 
+        // Extract raw f32 once — all arithmetic below is in radians
+        let heading = turtle_heading.value();
+
         // Calculate center based on direction
         // In screen coordinates (Y-down):
         // - Left turn (counter-clockwise visually): center is perpendicular-left from turtle's perspective
@@ -35,8 +74,8 @@ impl CircleGeometry {
         // - Right turn (clockwise visually): center is perpendicular-right from turtle's perspective
         //   which is heading + π/2 (rotated counter-clockwise from heading vector)
         let center_offset_angle = match direction {
-            CircleDirection::Left => turtle_heading - FRAC_PI_2,
+            CircleDirection::Left => heading - FRAC_PI_2,
-            CircleDirection::Right => turtle_heading + FRAC_PI_2,
+            CircleDirection::Right => heading + FRAC_PI_2,
         };
 
         let center = vec2(
@@ -46,8 +85,8 @@ impl CircleGeometry {
 
         // Angle from center back to turtle position
         let start_angle_from_center = match direction {
-            CircleDirection::Left => turtle_heading + FRAC_PI_2,
+            CircleDirection::Left => heading + FRAC_PI_2,
-            CircleDirection::Right => turtle_heading - FRAC_PI_2,
+            CircleDirection::Right => heading - FRAC_PI_2,
         };
 
         Self {
@@ -151,7 +190,7 @@ mod tests {
     fn test_circle_left_geometry() {
         let geom = CircleGeometry::new(
             vec2(0.0, 0.0),
-            0.0, // heading east (0 radians)
+            Radians::new(0.0), // heading east (0 radians)
             100.0,
             CircleDirection::Left,
         );
@@ -183,7 +222,7 @@ mod tests {
     fn test_circle_right_geometry() {
         let geom = CircleGeometry::new(
             vec2(0.0, 0.0),
-            0.0, // heading east
+            Radians::new(0.0), // heading east
             100.0,
             CircleDirection::Right,
         );

turtle-lib/src/command_behavior.rs

@@ -0,0 +1,150 @@
+//! Centralised behavioural contract for `TurtleCommand`.
+//!
+//! All knowledge about what a command does to `TurtleParams`, how long it
+//! animates, and whether it produces a drawable stroke lives here.
+//!
+//! Adding a new `TurtleCommand` variant requires editing this file (and
+//! `execute_command_side_effects` / `tessellate_command` in `execution.rs`
+//! if the variant has side effects or produces a mesh).
+
+use crate::circle_geometry::{CircleDirection, CircleGeometry};
+use crate::commands::TurtleCommand;
+use crate::general::{AnimationSpeed, Radians};
+use crate::state::TurtleParams;
+use crate::tweening::normalize_angle;
+use macroquad::prelude::vec2;
+
+impl TurtleCommand {
+    /// Apply this command's effect to `params` in place.
+    ///
+    /// This is the **single source of truth** for what a command changes in
+    /// `TurtleParams`. Used by:
+    /// - `execute_command()` — instant-mode path, after side-effects return `false`
+    /// - `TweenController::calculate_target_state()` — animated-mode target computation
+    ///
+    /// Variants handled by `execute_command_side_effects` (`BeginFill`, `EndFill`,
+    /// `PenUp`, `PenDown`, `WriteText`, `Reset`) are included here so that
+    /// `calculate_target_state` can produce a correct tween target.  In the
+    /// `execute_command()` call path those variants never reach this method because
+    /// `execute_command_side_effects` returns `true` and the caller returns early —
+    /// there is no double-application.
+    pub(crate) fn apply_to_params(&self, params: &mut TurtleParams) {
+        match self {
+            TurtleCommand::Move(dist) => {
+                let dx = dist * params.heading.cos();
+                let dy = dist * params.heading.sin();
+                params.position = vec2(params.position.x + dx, params.position.y + dy);
+            }
+            TurtleCommand::Turn(angle) => {
+                params.heading = normalize_angle(params.heading + angle.as_radians().value());
+            }
+            TurtleCommand::Circle {
+                radius,
+                angle,
+                direction,
+                ..
+            } => {
+                let geom = CircleGeometry::new(
+                    params.position,
+                    Radians::new(params.heading),
+                    *radius,
+                    *direction,
+                );
+                let angle_rad = angle.as_radians().value();
+                params.position = geom.position_at_angle(angle_rad);
+                params.heading = normalize_angle(match direction {
+                    CircleDirection::Left => params.heading - angle_rad,
+                    CircleDirection::Right => params.heading + angle_rad,
+                });
+            }
+            TurtleCommand::Goto(coord) => {
+                // Y-flip: turtle graphics Y+ = up; Macroquad Y+ = down
+                params.position = vec2(coord.x, -coord.y);
+            }
+            TurtleCommand::SetHeading(heading) => {
+                params.heading = normalize_angle(heading.value());
+            }
+            TurtleCommand::SetColor(color) => {
+                params.color = *color;
+            }
+            TurtleCommand::SetFillColor(color) => {
+                params.fill_color = *color;
+            }
+            TurtleCommand::SetPenWidth(width) => {
+                params.pen_width = *width;
+            }
+            TurtleCommand::SetSpeed(speed) => {
+                params.speed = *speed;
+            }
+            TurtleCommand::SetShape(shape) => {
+                params.shape = shape.clone();
+            }
+            TurtleCommand::PenUp => {
+                params.pen_down = false;
+            }
+            TurtleCommand::PenDown => {
+                params.pen_down = true;
+            }
+            TurtleCommand::ShowTurtle => {
+                params.visible = true;
+            }
+            TurtleCommand::HideTurtle => {
+                params.visible = false;
+            }
+            TurtleCommand::Reset => {
+                *params = TurtleParams::default();
+            }
+            // Fill/text commands do not change TurtleParams for tweening purposes;
+            // their effects are handled entirely by execute_command_side_effects.
+            TurtleCommand::BeginFill | TurtleCommand::EndFill | TurtleCommand::WriteText { .. } => {
+            }
+        }
+    }
+
+    /// Duration in seconds for this command's animation at the given speed.
+    ///
+    /// Returns `0.01` (minimum) for commands that have no animated component.
+    /// This is the **single source of truth**; replaces
+    /// `TweenController::calculate_duration_with_state` in `tweening.rs`.
+    pub(crate) fn animation_duration(&self, params: &TurtleParams, speed: AnimationSpeed) -> f64 {
+        let AnimationSpeed::Animated(mut spd) = speed else {
+            // Instant mode — duration is irrelevant; return the minimum so tweener
+            // infrastructure still has a valid duration if called accidentally.
+            return f64::from(0.01_f32);
+        };
+
+        // Exponential speed scaling for high values (matches original behaviour)
+        if spd > 100.0 {
+            spd *= spd / 100.0;
+        }
+
+        let base: f32 = match self {
+            TurtleCommand::Move(dist) => dist.abs() / spd,
+            TurtleCommand::Turn(angle) => angle.value().abs() / (spd * 1.8),
+            TurtleCommand::Circle { radius, angle, .. } => {
+                let arc_length = radius * angle.as_radians().value().abs();
+                arc_length / spd
+            }
+            TurtleCommand::Goto(target) => {
+                let dx = target.x - params.position.x;
+                let dy = target.y - params.position.y;
+                (dx * dx + dy * dy).sqrt() / spd
+            }
+            _ => 0.0,
+        };
+
+        f64::from(base.max(0.01))
+    }
+
+    /// Whether executing this command (when pen is down) produces a stroke or fill mesh.
+    ///
+    /// This is the **single source of truth**; replaces
+    /// `TweenController::command_creates_drawing` in `tweening.rs`.
+    #[must_use]
+    pub(crate) fn produces_drawing(&self) -> bool {
+        matches!(
+            self,
+            TurtleCommand::Move(_) | TurtleCommand::Circle { .. } | TurtleCommand::Goto(_)
+        )
+    }
+}

turtle-lib/src/commands.rs

@@ -1,6 +1,6 @@
 //! Turtle commands and command queue
 
-use crate::general::{AnimationSpeed, Color, Coordinate, FontSize, Precision};
+use crate::general::{AnimationSpeed, Color, Coordinate, Degrees, FontSize, Precision, Radians};
 use crate::shapes::TurtleShape;
 
 /// Individual turtle commands
@@ -9,13 +9,14 @@ pub enum TurtleCommand {
     // Movement (positive = forward, negative = backward)
     Move(Precision),
 
-    // Rotation (positive = right/clockwise, negative = left/counter-clockwise in degrees)
+    // Rotation (positive = right/clockwise, negative = left/counter-clockwise)
-    Turn(Precision),
+    // Stored in degrees — the natural unit at the user-facing API boundary.
+    Turn(Degrees),
 
     // Circle drawing
     Circle {
         radius: Precision,
-        angle: Precision, // degrees
+        angle: Degrees, // sweep angle — degrees, as supplied by the user
         steps: usize,
         direction: crate::circle_geometry::CircleDirection,
     },
@@ -33,7 +34,8 @@ pub enum TurtleCommand {
 
     // Position
     Goto(Coordinate),
-    SetHeading(Precision), // radians
+    /// Heading stored as radians — already converted by the builder.
+    SetHeading(Radians),
 
     // Visibility
     ShowTurtle,
@@ -53,11 +55,14 @@ pub enum TurtleCommand {
     Reset,
 }
 
-/// Queue of turtle commands with execution state
+/// A pure-data sequence of turtle commands.
+///
+/// `CommandQueue` is intentionally *not* an `Iterator` — it carries no cursor
+/// state.  Execution state ("which command are we on?") belongs to the
+/// consumer; `TweenController` owns the cursor that walks this queue.
 #[derive(Clone, Debug)]
 pub struct CommandQueue {
     commands: Vec<TurtleCommand>,
-    current_index: usize,
 }
 
 impl CommandQueue {
@@ -65,14 +70,12 @@ impl CommandQueue {
     pub fn new() -> Self {
         Self {
             commands: Vec::new(),
-            current_index: 0,
         }
     }
     #[must_use]
     pub fn with_capacity(capacity: usize) -> Self {
         Self {
             commands: Vec::with_capacity(capacity),
-            current_index: 0,
         }
     }
 
@@ -83,26 +86,22 @@ impl CommandQueue {
     pub fn extend(&mut self, commands: impl IntoIterator<Item = TurtleCommand>) {
         self.commands.extend(commands);
     }
+
+    /// Return a reference to the command at `index`, or `None` if out of range.
     #[must_use]
-    pub fn is_complete(&self) -> bool {
+    pub fn get(&self, index: usize) -> Option<&TurtleCommand> {
-        self.current_index >= self.commands.len()
+        self.commands.get(index)
-    }
-    pub fn reset(&mut self) {
-        self.current_index = 0;
     }
+
     #[must_use]
     pub fn len(&self) -> usize {
         self.commands.len()
     }
+
     #[must_use]
     pub fn is_empty(&self) -> bool {
         self.commands.is_empty()
     }
-
-    #[must_use]
-    pub fn remaining(&self) -> usize {
-        self.commands.len().saturating_sub(self.current_index)
-    }
 }
 
 impl Default for CommandQueue {
@@ -111,16 +110,16 @@ impl Default for CommandQueue {
     }
 }
 
-impl Iterator for CommandQueue {
+/// Consuming iteration — yields every command in order.
+///
+/// This is used by `CommandQueue::extend` and `TweenController::append_commands`
+/// to drain one queue into another.  It does *not* imply that `CommandQueue`
+/// itself is stateful; the cursor always lives in the consumer.
+impl IntoIterator for CommandQueue {
     type Item = TurtleCommand;
+    type IntoIter = std::vec::IntoIter<TurtleCommand>;
 
-    fn next(&mut self) -> Option<Self::Item> {
+    fn into_iter(self) -> Self::IntoIter {
-        if self.current_index < self.commands.len() {
+        self.commands.into_iter()
-            let cmd = self.commands[self.current_index].clone();
-            self.current_index += 1;
-            Some(cmd)
-        } else {
-            None
-        }
     }
 }

turtle-lib/src/commands_channel.rs

@@ -76,7 +76,7 @@ pub struct TurtleCommandSender {
 ///
 /// Paired with `TurtleCommandSender` via `turtle_command_channel()`.
 /// Automatically managed by `TurtleApp::process_commands()`.
-pub struct TurtleCommandReceiver {
+pub(crate) struct TurtleCommandReceiver {
     turtle_id: usize,
     rx: Receiver<CommandQueue>,
 }
@@ -212,7 +212,7 @@ impl TurtleCommandReceiver {
 /// # }
 /// ```
 #[must_use]
-pub fn turtle_command_channel(
+pub(crate) fn turtle_command_channel(
     turtle_id: usize,
     buffer_size: usize,
 ) -> (TurtleCommandSender, TurtleCommandReceiver) {

turtle-lib/src/drawing.rs

@@ -12,56 +12,9 @@ use macroquad::prelude::*;
 // See https://easings.net/ for visual demonstrations
 use tween::CubicInOut;
 
-/// Render the entire turtle world
+/// Render the turtle world with active tween visualization.
-pub fn render_world(world: &TurtleWorld) {
-    // Update camera zoom based on current screen size to prevent stretching
-    let camera = Camera2D {
-        zoom: vec2(1.0 / screen_width() * 2.0, 1.0 / screen_height() * 2.0),
-        target: world.camera.target,
-        ..Default::default()
-    };
-
-    // Set camera
-    set_camera(&camera);
-
-    // Draw all accumulated commands from all turtles
-    for turtle in &world.turtles {
-        for cmd in &turtle.commands {
-            match cmd {
-                DrawCommand::Mesh { data, source: _ } => {
-                    // Rendering wie bisher
-                    draw_mesh(&data.to_mesh());
-                    // Hier könnte man das source für Debug/Export loggen
-                }
-                DrawCommand::Text {
-                    text,
-                    position,
-                    heading,
-                    font_size,
-                    color,
-                    source: _,
-                } => {
-                    draw_text_command(text, *position, *heading, *font_size, *color);
-                    // Hier könnte man das source für Debug/Export loggen
-                }
-            }
-        }
-    }
-
-    // Draw all visible turtles
-    for turtle in &world.turtles {
-        if turtle.params.visible {
-            draw_turtle(&turtle.params);
-        }
-    }
-
-    // Reset to default camera
-    set_default_camera();
-}
-
-/// Render the turtle world with active tween visualization
 #[allow(clippy::too_many_lines)]
-pub fn render_world_with_tweens(world: &TurtleWorld, zoom_level: f32) {
+pub(crate) fn render_world_with_tweens(world: &TurtleWorld, zoom_level: f32) {
     // Update camera zoom based on current screen size to prevent stretching
     // Apply user zoom level by dividing by it (smaller zoom value = more zoomed in)
     let camera = Camera2D {
@@ -80,7 +33,7 @@ pub fn render_world_with_tweens(world: &TurtleWorld, zoom_level: f32) {
     for turtle in &world.turtles {
         for cmd in &turtle.commands {
             match cmd {
-                DrawCommand::Mesh { data, source: _ } => {
+                DrawCommand::Mesh { data } => {
                     draw_mesh(&data.to_mesh());
                 }
                 DrawCommand::Text {
@@ -89,7 +42,6 @@ pub fn render_world_with_tweens(world: &TurtleWorld, zoom_level: f32) {
                     heading,
                     font_size,
                     color,
-                    source: _,
                 } => {
                     draw_text_command(text, *position, *heading, *font_size, *color);
                 }
@@ -176,40 +128,32 @@ pub fn render_world_with_tweens(world: &TurtleWorld, zoom_level: f32) {
                     } = &tween.command
                     {
                         // Calculate partial arc vertices based on current progress
-                        use crate::circle_geometry::CircleGeometry;
+                        use crate::circle_geometry::{arc_points, CircleGeometry};
+                        use crate::general::Radians;
                         let geom = CircleGeometry::new(
                             tween.start_params.position,
-                            tween.start_params.heading,
+                            Radians::new(tween.start_params.heading),
                             *radius,
                             *direction,
-                        ); // Calculate progress
+                        );
                         let elapsed = get_time() - tween.start_time;
                         let progress = (elapsed / tween.duration).min(1.0);
                         let eased_progress = CubicInOut.tween(1.0, progress as f32);
 
-                        // Generate arc vertices for the partial arc
+                        // Delegate to the shared arc_points function — same sampling
-                        let num_samples = *steps.max(&1);
+                        // strategy as tessellate_arc, eliminating the divergence.
                         let samples_to_draw =
-                            ((num_samples as f32 * eased_progress) as usize).max(1);
+                            (((*steps).max(1) as f32 * eased_progress) as usize).max(1);
-
+                        let sweep_so_far = angle.as_radians().value() * eased_progress;
-                        for i in 1..=samples_to_draw {
+                        for pt in arc_points(
-                            let sample_progress = i as f32 / num_samples as f32;
+                            geom.center,
-                            let current_angle = match direction {
+                            *radius,
-                                crate::circle_geometry::CircleDirection::Left => {
+                            geom.start_angle_from_center,
-                                    geom.start_angle_from_center
+                            sweep_so_far,
-                                        - angle.to_radians() * sample_progress
+                            samples_to_draw,
-                                }
+                            *direction,
-                                crate::circle_geometry::CircleDirection::Right => {
+                        ) {
-                                    geom.start_angle_from_center
+                            current_preview.push(pt);
-                                        + angle.to_radians() * sample_progress
-                                }
-                            };
-
-                            let vertex = Vec2::new(
-                                geom.center.x + radius * current_angle.cos(),
-                                geom.center.y + radius * current_angle.sin(),
-                            );
-                            current_preview.push(vertex);
                         }
                     } else if matches!(
                         &tween.command,
@@ -347,18 +291,19 @@ fn draw_text_command(
 fn draw_tween_arc(
     tween: &crate::tweening::CommandTween,
     radius: f32,
-    total_angle: f32,
+    total_angle: crate::general::Degrees,
     steps: usize,
     direction: CircleDirection,
 ) {
+    use crate::general::Radians;
     let geom = CircleGeometry::new(
         tween.start_params.position,
-        tween.start_params.heading,
+        Radians::new(tween.start_params.heading),
         radius,
         direction,
     );
 
-    // Debug: draw center using Lyon tessellation
+    // Draw center using Lyon tessellation this helps visualizing what is done.
     if let Ok(mesh_data) = crate::tessellation::tessellate_circle(geom.center, 5.0, GRAY, true, 1.0)
     {
         draw_mesh(&mesh_data.to_mesh());
@@ -375,7 +320,7 @@ fn draw_tween_arc(
         geom.center,
         radius,
         geom.start_angle_from_center.to_degrees(),
-        total_angle * progress,
+        total_angle.value() * progress,
         tween.start_params.color,
         tween.start_params.pen_width,
         ((steps as f32 * progress).ceil() as usize).max(1),
@@ -386,7 +331,7 @@ fn draw_tween_arc(
 }
 
 /// Draw the turtle shape
-pub fn draw_turtle(turtle_params: &TurtleParams) {
+pub(crate) fn draw_turtle(turtle_params: &TurtleParams) {
     let rotated_vertices = turtle_params.shape.rotated_vertices(turtle_params.heading);
 
     if turtle_params.shape.filled {

turtle-lib/src/execution.rs

@@ -2,51 +2,120 @@
 
 use crate::circle_geometry::{CircleDirection, CircleGeometry};
 use crate::commands::TurtleCommand;
-use crate::state::{DrawCommand, Turtle, TurtleParams, TurtleWorld};
+use crate::general::{Coordinate, Radians};
+use crate::state::{DrawCommand, FillState, Turtle, TurtleParams, TurtleWorld};
 use crate::tessellation;
 use macroquad::prelude::*;
 
 #[cfg(test)]
 use crate::general::AnimationSpeed;
 
-/// Execute side effects for commands that don't involve movement
+/// Close the current open fill contour (factored out of `Turtle::close_fill_contour`).
-/// Returns true if the command was handled (caller should skip movement processing)
+fn close_fill_contour(turtle_id: usize, filling: &mut Option<FillState>) {
-#[allow(clippy::too_many_lines)]
+    if let Some(ref mut fill_state) = filling {
-pub fn execute_command_side_effects(command: &TurtleCommand, state: &mut Turtle) -> bool {
+        tracing::debug!(
-    match command {
+            turtle_id,
-        TurtleCommand::BeginFill => {
+            vertices = fill_state.current_contour.len(),
-            if state.filling.is_some() {
+            "close_fill_contour called"
+        );
+        if fill_state.current_contour.len() >= 2 {
+            tracing::debug!(
+                turtle_id,
+                vertices = fill_state.current_contour.len(),
+                first_x = fill_state.current_contour[0].x,
+                first_y = fill_state.current_contour[0].y,
+                last_x = fill_state.current_contour[fill_state.current_contour.len() - 1].x,
+                last_y = fill_state.current_contour[fill_state.current_contour.len() - 1].y,
+                "Closing contour"
+            );
+            let contour = std::mem::take(&mut fill_state.current_contour);
+            fill_state.contours.push(contour);
+            tracing::debug!(
+                turtle_id,
+                completed_contours = fill_state.contours.len(),
+                "Contour moved to completed list"
+            );
+        } else if !fill_state.current_contour.is_empty() {
             tracing::warn!(
-                    turtle_id = state.turtle_id,
+                turtle_id,
-                    "begin_fill() called while already filling"
+                vertices = fill_state.current_contour.len(),
+                "Current contour has insufficient vertices, not closing"
+            );
+        } else {
+            tracing::warn!(turtle_id, "Current contour is empty, nothing to close");
+        }
+    } else {
+        tracing::warn!(
+            turtle_id,
+            "close_fill_contour called but no active fill state"
         );
     }
-            let fill_color = state.params.fill_color.unwrap_or_else(|| {
+}
-                tracing::warn!(
+
-                    turtle_id = state.turtle_id,
+/// Begin a new fill contour at `position` (factored out of `Turtle::start_fill_contour`).
-                    "No fill_color set, using black"
+fn start_fill_contour(turtle_id: usize, position: Coordinate, filling: &mut Option<FillState>) {
+    if let Some(ref mut fill_state) = filling {
+        tracing::debug!(
+            x = position.x,
+            y = position.y,
+            completed_contours = fill_state.contours.len(),
+            turtle_id,
+            "Starting new contour"
         );
+        fill_state.current_contour = vec![position];
+    }
+}
+
+/// Execute side effects for commands that don't involve movement.
+///
+/// Returns `true` if the command was fully handled; the caller should skip
+/// params-update and tessellation when this returns `true`.
+///
+/// Accepts the three logically-separate pieces of turtle state as disjoint
+/// mutable borrows so that this function can be called from
+/// `TweenController::update(&mut self, …)` without requiring a `&mut Turtle`.
+#[allow(clippy::too_many_lines)]
+pub(crate) fn execute_command_side_effects(
+    command: &TurtleCommand,
+    turtle_id: usize,
+    params: &mut TurtleParams,
+    filling: &mut Option<FillState>,
+    commands: &mut Vec<DrawCommand>,
+    svg_log: &mut crate::state::SvgLog,
+) -> bool {
+    match command {
+        TurtleCommand::BeginFill => {
+            if filling.is_some() {
+                tracing::warn!(turtle_id, "begin_fill() called while already filling");
+            }
+            let fill_color = params.fill_color.unwrap_or_else(|| {
+                tracing::warn!(turtle_id, "No fill_color set, using black");
                 BLACK
             });
-            state.begin_fill(fill_color);
+            *filling = Some(FillState {
+                start_position: params.position,
+                contours: Vec::new(),
+                current_contour: vec![params.position],
+                fill_color,
+            });
             true
         }
         TurtleCommand::EndFill => {
-            if let Some(mut fill_state) = state.filling.take() {
+            if let Some(mut fill_state) = filling.take() {
                 if !fill_state.current_contour.is_empty() {
                     fill_state.contours.push(fill_state.current_contour);
                 }
 
                 let span = tracing::debug_span!(
                     "end_fill",
-                    turtle_id = state.turtle_id,
+                    turtle_id,
                     contours = fill_state.contours.len()
                 );
                 let _enter = span.enter();
 
                 for (i, contour) in fill_state.contours.iter().enumerate() {
                     tracing::debug!(
-                        turtle_id = state.turtle_id,
+                        turtle_id,
                         contour_idx = i,
                         vertices = contour.len(),
                         "Contour info"
@@ -59,85 +128,69 @@ pub fn execute_command_side_effects(command: &TurtleCommand, state: &mut Turtle)
                         fill_state.fill_color,
                     ) {
                         tracing::debug!(
-                            turtle_id = state.turtle_id,
+                            turtle_id,
                             contours = fill_state.contours.len(),
                             "Successfully created fill mesh - persisting to commands"
                         );
-                        state.commands.push(DrawCommand::Mesh {
+                        commands.push(DrawCommand::Mesh { data: mesh_data });
-                            data: mesh_data,
+                        #[cfg(feature = "svg")]
-                            source: crate::state::TurtleSource {
+                        svg_log.push(crate::state::SvgRecord::Fill {
-                                command: crate::commands::TurtleCommand::EndFill,
+                            contours: fill_state.contours,
-                                color: state.params.color,
                             fill_color: fill_state.fill_color,
-                                pen_width: state.params.pen_width,
+                            stroke_color: params.color,
-                                start_position: fill_state.start_position,
-                                end_position: fill_state.start_position,
-                                start_heading: state.params.heading,
-                                contours: Some(fill_state.contours.clone()),
-                            },
                         });
                     } else {
-                        tracing::error!(
+                        tracing::error!(turtle_id, "Failed to tessellate contours");
-                            turtle_id = state.turtle_id,
-                            "Failed to tessellate contours"
-                        );
                     }
                 }
             } else {
-                tracing::warn!(
+                tracing::warn!(turtle_id, "end_fill() called without begin_fill()");
-                    turtle_id = state.turtle_id,
-                    "end_fill() called without begin_fill()"
-                );
             }
             true
         }
         TurtleCommand::PenUp => {
-            state.params.pen_down = false;
+            params.pen_down = false;
-            if state.filling.is_some() {
+            if filling.is_some() {
-                tracing::debug!(
+                tracing::debug!(turtle_id, "PenUp: Closing current contour");
-                    turtle_id = state.turtle_id,
-                    "PenUp: Closing current contour"
-                );
             }
-            state.close_fill_contour();
+            close_fill_contour(turtle_id, filling);
             true
         }
         TurtleCommand::PenDown => {
-            state.params.pen_down = true;
+            params.pen_down = true;
-            if state.filling.is_some() {
+            if filling.is_some() {
                 tracing::debug!(
-                    turtle_id = state.turtle_id,
+                    turtle_id,
-                    x = state.params.position.x,
+                    x = params.position.x,
-                    y = state.params.position.y,
+                    y = params.position.y,
                     "PenDown: Starting new contour"
                 );
             }
-            state.start_fill_contour();
+            start_fill_contour(turtle_id, params.position, filling);
             true
         }
 
         TurtleCommand::Reset => {
-            state.reset();
+            commands.clear();
+            svg_log.clear();
+            *filling = None;
+            *params = TurtleParams::default();
             true
         }
 
         TurtleCommand::WriteText { text, font_size } => {
-            state.commands.push(DrawCommand::Text {
+            commands.push(DrawCommand::Text {
                 text: text.clone(),
-                position: state.params.position,
+                position: params.position,
-                heading: state.params.heading,
+                heading: params.heading,
                 font_size: *font_size,
-                color: state.params.color,
+                color: params.color,
-                source: crate::state::TurtleSource {
+            });
-                    command: command.clone(),
+            #[cfg(feature = "svg")]
-                    color: state.params.color,
+            svg_log.push(crate::state::SvgRecord::Text {
-                    fill_color: state.params.fill_color.unwrap_or(BLACK),
+                text: text.clone(),
-                    pen_width: state.params.pen_width,
+                position: params.position,
-                    start_position: state.params.position,
+                color: params.color,
-                    end_position: state.params.position,
-                    start_heading: state.params.heading,
-                    contours: None,
-                },
             });
             true
         }
@@ -157,14 +210,23 @@ pub fn execute_command_side_effects(command: &TurtleCommand, state: &mut Turtle)
     }
 }
 
-/// Record fill vertices after movement commands have updated state
+/// Record fill vertices after movement commands have updated state.
-#[tracing::instrument]
+///
-pub fn record_fill_vertices_after_movement(
+/// `start_state` is the params snapshot taken **before** the command ran.
+/// `params` is the current (post-movement) state — `params.position` is the
+/// endpoint that gets pushed into the active fill contour.
+///
+/// Accepts disjoint borrows so it can be called from `TweenController::update`
+/// without needing a `&mut Turtle`.
+#[tracing::instrument(skip(params, filling))]
+pub(crate) fn record_fill_vertices_after_movement(
     command: &TurtleCommand,
     start_state: &TurtleParams,
-    state: &mut Turtle,
+    turtle_id: usize,
+    params: &TurtleParams,
+    filling: &mut Option<FillState>,
 ) {
-    if state.filling.is_none() {
+    if filling.is_none() {
         return;
     }
 
@@ -177,268 +239,242 @@ pub fn record_fill_vertices_after_movement(
         } => {
             let geom = CircleGeometry::new(
                 start_state.position,
-                start_state.heading,
+                Radians::new(start_state.heading),
                 *radius,
                 *direction,
             );
-            state.record_fill_vertices_for_arc(
+            if let Some(ref mut fill_state) = filling {
-                geom.center,
+                if params.pen_down {
-                *radius,
+                    let num_samples = (*steps as u32).max(1);
-                geom.start_angle_from_center,
+                    tracing::trace!(
-                angle.to_radians(),
+                        turtle_id,
-                *direction,
+                        center_x = geom.center.x,
-                *steps as u32,
+                        center_y = geom.center.y,
+                        radius,
+                        steps,
+                        num_samples,
+                        "Recording arc vertices"
                     );
+                    for i in 1..=num_samples {
+                        let progress = i as f32 / num_samples as f32;
+                        let current_angle = match direction {
+                            CircleDirection::Left => {
+                                geom.start_angle_from_center - angle.as_radians().value() * progress
+                            }
+                            CircleDirection::Right => {
+                                geom.start_angle_from_center + angle.as_radians().value() * progress
+                            }
+                        };
+                        let vertex = Coordinate::new(
+                            geom.center.x + radius * current_angle.cos(),
+                            geom.center.y + radius * current_angle.sin(),
+                        );
+                        tracing::trace!(
+                            turtle_id,
+                            vertex_idx = i,
+                            x = vertex.x,
+                            y = vertex.y,
+                            angle_degrees = current_angle.to_degrees(),
+                            "Arc vertex"
+                        );
+                        fill_state.current_contour.push(vertex);
+                    }
+                }
+            }
         }
         TurtleCommand::Move(_) | TurtleCommand::Goto(_) => {
-            state.record_fill_vertex();
+            if let Some(ref mut fill_state) = filling {
+                if params.pen_down {
+                    tracing::trace!(
+                        turtle_id,
+                        x = params.position.x,
+                        y = params.position.y,
+                        vertices = fill_state.current_contour.len() + 1,
+                        "Adding vertex to current contour"
+                    );
+                    fill_state.current_contour.push(params.position);
+                } else {
+                    tracing::trace!(turtle_id, "Skipping vertex (pen is up)");
+                }
+            }
         }
         _ => {}
     }
 }
 
-/// Execute a single turtle command, updating state and adding draw commands
+/// Tessellate a completed movement command into a [`DrawCommand`] mesh.
-#[tracing::instrument]
+///
-#[allow(clippy::too_many_lines)]
+/// Returns `None` if the pen was up or the command does not produce a drawing.
-pub fn execute_command(command: &TurtleCommand, state: &mut Turtle) {
+///
-    // Try to execute as side-effect-only command first
+/// `end_position` is the turtle's position after the command completed:
-    if execute_command_side_effects(command, state) {
+/// - instant-mode: `state.params.position` after [`TurtleCommand::apply_to_params`]
-        return; // Command fully handled
+/// - animated-mode: `tween.target_params.position` when the tween finishes
-    }
+///
-
+/// This is the **single** tessellation site for all committed line/arc meshes.
-    // Store start state for fill vertex recording
+/// It replaces both the inline tessellation inside `execute_command` and the
-    let start_state = state.clone();
+/// now-deleted `add_draw_for_completed_tween`.
-
+pub(crate) fn tessellate_command(
-    // Execute movement and appearance commands
-    match command {
-        TurtleCommand::Move(distance) => {
-            let start = state.params.position;
-            let dx = distance * state.params.heading.cos();
-            let dy = distance * state.params.heading.sin();
-            state.params.position =
-                vec2(state.params.position.x + dx, state.params.position.y + dy);
-
-            if state.params.pen_down {
-                // Draw line segment with round caps (caps handled by tessellate_stroke)
-                if let Ok(mesh_data) = tessellation::tessellate_stroke(
-                    &[start, state.params.position],
-                    state.params.color,
-                    state.params.pen_width,
-                    false, // not closed
-                ) {
-                    state.commands.push(DrawCommand::Mesh {
-                        data: mesh_data,
-                        source: crate::state::TurtleSource {
-                            command: command.clone(),
-                            color: state.params.color,
-                            fill_color: state.params.fill_color.unwrap_or(BLACK),
-                            pen_width: state.params.pen_width,
-                            start_position: start,
-                            end_position: state.params.position,
-                            start_heading: state.params.heading,
-                            contours: None,
-                        },
-                    });
-                }
-            }
-        }
-
-        TurtleCommand::Turn(degrees) => {
-            state.params.heading += degrees.to_radians();
-        }
-
-        TurtleCommand::Circle {
-            radius,
-            angle,
-            steps,
-            direction,
-        } => {
-            let start_heading = state.params.heading;
-            let geom =
-                CircleGeometry::new(state.params.position, start_heading, *radius, *direction);
-
-            if state.params.pen_down {
-                // Use Lyon to tessellate the arc
-                if let Ok(mesh_data) = tessellation::tessellate_arc(
-                    geom.center,
-                    *radius,
-                    geom.start_angle_from_center.to_degrees(),
-                    *angle,
-                    state.params.color,
-                    state.params.pen_width,
-                    *steps,
-                    *direction,
-                ) {
-                    state.commands.push(DrawCommand::Mesh {
-                        data: mesh_data,
-                        source: crate::state::TurtleSource {
-                            command: command.clone(),
-                            color: state.params.color,
-                            fill_color: state.params.fill_color.unwrap_or(BLACK),
-                            pen_width: state.params.pen_width,
-                            start_position: state.params.position,
-                            end_position: geom.position_at_angle(angle.to_radians()),
-                            start_heading,
-                            contours: None,
-                        },
-                    });
-                }
-            }
-
-            // Update turtle position and heading
-            state.params.position = geom.position_at_angle(angle.to_radians());
-            state.params.heading = match direction {
-                CircleDirection::Left => start_heading - angle.to_radians(),
-                CircleDirection::Right => start_heading + angle.to_radians(),
-            };
-        }
-
-        TurtleCommand::Goto(coord) => {
-            let start = state.params.position;
-            // Flip Y coordinate: turtle graphics uses Y+ = up, but Macroquad uses Y+ = down
-            state.params.position = vec2(coord.x, -coord.y);
-
-            if state.params.pen_down {
-                // Draw line segment with round caps
-                if let Ok(mesh_data) = tessellation::tessellate_stroke(
-                    &[start, state.params.position],
-                    state.params.color,
-                    state.params.pen_width,
-                    false, // not closed
-                ) {
-                    state.commands.push(DrawCommand::Mesh {
-                        data: mesh_data,
-                        source: crate::state::TurtleSource {
-                            command: command.clone(),
-                            color: state.params.color,
-                            fill_color: state.params.fill_color.unwrap_or(BLACK),
-                            pen_width: state.params.pen_width,
-                            start_position: start,
-                            end_position: state.params.position,
-                            start_heading: state.params.heading,
-                            contours: None,
-                        },
-                    });
-                }
-            }
-        }
-
-        // Appearance commands
-        TurtleCommand::SetColor(color) => state.params.color = *color,
-        TurtleCommand::SetFillColor(color) => state.params.fill_color = *color,
-        TurtleCommand::SetPenWidth(width) => state.params.pen_width = *width,
-        TurtleCommand::SetSpeed(speed) => state.set_speed(*speed),
-        TurtleCommand::SetShape(shape) => state.params.shape = shape.clone(),
-        TurtleCommand::SetHeading(heading) => state.params.heading = *heading,
-        TurtleCommand::ShowTurtle => state.params.visible = true,
-        TurtleCommand::HideTurtle => state.params.visible = false,
-
-        // Reset
-        TurtleCommand::Reset => {
-            state.reset();
-        }
-
-        _ => {} // Already handled by execute_command_side_effects
-    }
-
-    // Record fill vertices AFTER movement
-    record_fill_vertices_after_movement(command, &start_state.params, state);
-}
-
-/// Execute command on a specific turtle by ID
-pub fn execute_command_with_id(command: &TurtleCommand, turtle_id: usize, world: &mut TurtleWorld) {
-    // Clone turtle state to avoid borrow checker issues
-    if let Some(turtle) = world.get_turtle(turtle_id) {
-        let mut state = turtle.clone();
-        execute_command(command, &mut state);
-        // Update the turtle state back
-        if let Some(turtle_mut) = world.get_turtle_mut(turtle_id) {
-            *turtle_mut = state;
-        }
-    }
-}
-
-/// Add drawing command for a completed tween
-pub fn add_draw_for_completed_tween(
     command: &TurtleCommand,
-    start_state: &TurtleParams,
+    start: &TurtleParams,
-    end_state: &mut TurtleParams,
+    end_position: Vec2,
 ) -> Option<DrawCommand> {
+    if !start.pen_down || !command.produces_drawing() {
+        return None;
+    }
+
     match command {
         TurtleCommand::Move(_) | TurtleCommand::Goto(_) => {
-            if start_state.pen_down {
+            let mesh_data = tessellation::tessellate_stroke(
-                if let Ok(mesh_data) = tessellation::tessellate_stroke(
+                &[start.position, end_position],
-                    &[start_state.position, end_state.position],
+                start.color,
-                    start_state.color,
+                start.pen_width,
-                    start_state.pen_width,
                 false,
-                ) {
+            )
-                    return Some(DrawCommand::Mesh {
+            .ok()?;
-                        data: mesh_data,
+
-                        source: crate::state::TurtleSource {
+            Some(DrawCommand::Mesh { data: mesh_data })
-                            command: command.clone(),
-                            color: start_state.color,
-                            fill_color: start_state.fill_color.unwrap_or(BLACK),
-                            pen_width: start_state.pen_width,
-                            start_position: start_state.position,
-                            end_position: end_state.position,
-                            start_heading: start_state.heading,
-                            contours: None,
-                        },
-                    });
-                }
-            }
         }
+
         TurtleCommand::Circle {
             radius,
             angle,
             steps,
             direction,
         } => {
-            if start_state.pen_down {
+            use crate::circle_geometry::CircleGeometry;
             let geom = CircleGeometry::new(
-                    start_state.position,
+                start.position,
-                    start_state.heading,
+                Radians::new(start.heading),
                 *radius,
                 *direction,
             );
-                if let Ok(mesh_data) = tessellation::tessellate_arc(
+            let mesh_data = tessellation::tessellate_arc(
                 geom.center,
                 *radius,
                 geom.start_angle_from_center.to_degrees(),
-                    *angle,
+                angle.value(),
-                    start_state.color,
+                start.color,
-                    start_state.pen_width,
+                start.pen_width,
                 *steps,
                 *direction,
-                ) {
+            )
-                    return Some(DrawCommand::Mesh {
+            .ok()?;
-                        data: mesh_data,
+
-                        source: crate::state::TurtleSource {
+            Some(DrawCommand::Mesh { data: mesh_data })
-                            command: command.clone(),
+        }
-                            color: start_state.color,
+
-                            fill_color: start_state.fill_color.unwrap_or(BLACK),
+        // `produces_drawing()` guards entry — this arm is only reachable if
-                            pen_width: start_state.pen_width,
+        // `produces_drawing` and the match above diverge, which would be a bug.
-                            start_position: start_state.position,
+        _ => None,
-                            end_position: end_state.position,
+    }
-                            start_heading: start_state.heading,
+}
-                            contours: None,
+
-                        },
+/// Push an [`SvgRecord`] for a completed line or arc drawing command.
+///
+/// Only compiled when the `svg` feature is enabled.
+/// Must be called at the same call sites as `tessellate_command` so that
+/// `svg_log` stays in sync with `commands`.
+#[cfg(feature = "svg")]
+pub(crate) fn push_svg_for_draw(
+    command: &TurtleCommand,
+    start: &TurtleParams,
+    end_position: Vec2,
+    svg_log: &mut crate::state::SvgLog,
+) {
+    use crate::state::SvgRecord;
+    match command {
+        TurtleCommand::Move(_) | TurtleCommand::Goto(_) => {
+            svg_log.push(SvgRecord::Line {
+                start: start.position,
+                end: end_position,
+                color: start.color,
+                pen_width: start.pen_width,
             });
         }
+        TurtleCommand::Circle {
+            radius,
+            angle,
+            direction,
+            ..
+        } => {
+            svg_log.push(SvgRecord::Arc {
+                start_position: start.position,
+                start_heading: start.heading,
+                radius: *radius,
+                angle: *angle,
+                direction: *direction,
+                color: start.color,
+                pen_width: start.pen_width,
+            });
         }
+        _ => {}
     }
-        _ => (),
+}
+
+/// Execute a single turtle command, updating state and adding draw commands.
+#[tracing::instrument(skip(state))]
+pub(crate) fn execute_command(command: &TurtleCommand, state: &mut Turtle) {
+    // Phase 1: side effects (fills, pen contours, reset, text).
+    // Returns true if the command is fully handled — no params update or tessellation needed.
+    if execute_command_side_effects(
+        command,
+        state.turtle_id,
+        &mut state.params,
+        &mut state.filling,
+        &mut state.commands,
+        &mut state.svg_log,
+    ) {
+        return;
+    }
+
+    // Phase 2: update TurtleParams (position, heading, colour, speed, etc.)
+    let start_params = state.params.clone();
+    command.apply_to_params(&mut state.params);
+
+    // Phase 3: record fill vertices after movement (must follow params update)
+    record_fill_vertices_after_movement(
+        command,
+        &start_params,
+        state.turtle_id,
+        &state.params,
+        &mut state.filling,
+    );
+
+    // Phase 4: tessellate, push SVG record, and persist the committed drawing
+    if let Some(draw_cmd) = tessellate_command(command, &start_params, state.params.position) {
+        #[cfg(feature = "svg")]
+        push_svg_for_draw(
+            command,
+            &start_params,
+            state.params.position,
+            &mut state.svg_log,
+        );
+        state.commands.push(draw_cmd);
+    }
+}
+
+/// Execute command on a specific turtle by ID.
+///
+/// There is no ownership conflict here: `execute_command` only needs `&mut Turtle`
+/// and never touches `TurtleWorld`, so we can obtain the mutable reference directly
+/// from `get_turtle_mut` without any intermediate clone.
+pub(crate) fn execute_command_with_id(
+    command: &TurtleCommand,
+    turtle_id: usize,
+    world: &mut TurtleWorld,
+) {
+    if let Some(turtle) = world.get_turtle_mut(turtle_id) {
+        execute_command(command, turtle);
     }
-    None
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
     use crate::commands::TurtleCommand;
+    use crate::general::Degrees;
     use crate::shapes::TurtleShape;
-    use crate::TweenController;
+    use crate::tweening::TweenController;
 
     #[test]
     fn test_forward_left_forward() {
@@ -461,6 +497,7 @@ mod tests {
             },
             filling: None,
             commands: Vec::new(),
+            svg_log: crate::state::SvgLog::default(),
             tween_controller: TweenController::default(),
         };
 
@@ -500,7 +537,7 @@ mod tests {
 
         // Left 90 degrees - should face north (heading decreases by 90°)
         // In screen coords: north = -90° = -π/2
-        execute_command(&TurtleCommand::Turn(-90.0), &mut state);
+        execute_command(&TurtleCommand::Turn(Degrees::new(-90.0)), &mut state);
         assert!(
             (state.params.position.x - 100.0).abs() < 0.01,
             "After left(90): x = {}",

turtle-lib/src/export.rs

@@ -1,22 +1,23 @@
-//! Export-Backend-Trait und zentrale Export-Typen
+//! Export backend trait and core export types.
 
 use crate::state::TurtleWorld;
+use crate::TurtlePlan;
 
 #[derive(Debug)]
 pub enum ExportError {
     Io(std::io::Error),
     Format(String),
-    // Weitere Formate können ergänzt werden
+    // Additional formats can be added here.
 }
 
 #[derive(Clone, Copy, Debug)]
 pub enum DrawingFormat {
     #[cfg(feature = "svg")]
     Svg,
-    // Weitere Formate wie Png, Pdf, ...
+    // Additional formats: Png, Pdf, …
 }
 
-pub trait DrawingExporter {
+pub(crate) trait DrawingExporter {
     /// Export the drawing to the specified format and filename
     ///
     /// # Errors
@@ -24,3 +25,62 @@ pub trait DrawingExporter {
     /// Returns an error if the export fails (e.g., file I/O error)
     fn export(&self, world: &TurtleWorld, filename: &str) -> Result<(), ExportError>;
 }
+
+pub(crate) fn parse_svg_export_arg() -> Option<String> {
+    let args: Vec<String> = std::env::args().collect();
+    let mut i = 1;
+    while i < args.len() {
+        if args[i] == "--export-svg" && i + 1 < args.len() {
+            return Some(args[i + 1].clone());
+        }
+        i += 1;
+    }
+    None
+}
+
+/// Handle the optional `--export-svg` CLI flag.
+///
+/// The feature gating lives inside `turtle-lib`, so the `turtle_main` macro
+/// no longer needs to reference cfg flags from the consuming crate.
+pub fn handle_svg_export<F>(build_commands: F)
+where
+    F: FnMut(&mut TurtlePlan),
+{
+    // Avoid unused warnings when the feature is disabled
+    let _ = &build_commands;
+
+    if let Some(filename) = parse_svg_export_arg() {
+        #[cfg(feature = "svg")]
+        {
+            let mut build_commands = build_commands;
+            let mut turtle = crate::create_turtle_plan();
+            build_commands(&mut turtle);
+
+            let mut app = crate::TurtleApp::new().with_commands(turtle.build());
+            app.set_all_turtles_speed(crate::AnimationSpeed::Instant(1000));
+
+            while !app.all_animations_complete() {
+                app.update();
+            }
+
+            match app.export_drawing(&filename, crate::export::DrawingFormat::Svg) {
+                Ok(_) => {
+                    println!("SVG exported successfully to: {}", filename);
+                    std::process::exit(0);
+                }
+                Err(e) => {
+                    eprintln!("Error exporting SVG: {:?}", e);
+                    std::process::exit(1);
+                }
+            }
+        }
+
+        #[cfg(not(feature = "svg"))]
+        {
+            let _ = &filename;
+            eprintln!("Error: SVG export feature is not enabled.");
+            eprintln!("Please rebuild with --features svg");
+            std::process::exit(1);
+        }
+    }
+}

turtle-lib/src/export_svg.rs

@@ -1,13 +1,12 @@
-//! SVG-Export-Backend für TurtleWorld
+//! SVG export backend for `TurtleWorld`.
 
 #[cfg(feature = "svg")]
 pub mod svg_export {
-    use crate::commands::TurtleCommand;
     use crate::export::{DrawingExporter, ExportError};
-    use crate::state::{DrawCommand, TurtleWorld};
+    use crate::state::{SvgRecord, TurtleWorld};
     use std::fs::File;
     use svg::{
-        node::element::{Circle, Line, Polygon, Text as SvgText},
+        node::element::{Circle, Line, Text as SvgText},
         Document,
     };
 
@@ -37,47 +36,50 @@ pub mod svg_export {
             }
 
             for turtle in &world.turtles {
-                for cmd in &turtle.commands {
+                for record in &turtle.svg_log.records {
-                    match cmd {
+                    match record {
-                        DrawCommand::Mesh { source, .. } => {
+                        SvgRecord::Line {
-                            match &source.command {
+                            start,
-                                TurtleCommand::Move(_) | TurtleCommand::Goto(_) => {
+                            end,
-                                    // Linie als <line>
+                            color,
-                                    let start = source.start_position;
+                            pen_width,
-                                    let end = source.end_position;
+                        } => {
                             update_bounds(
-                                        &mut min_x, &mut max_x, &mut min_y, &mut max_y, start.x,
+                                &mut min_x, &mut max_x, &mut min_y, &mut max_y, start.x, start.y,
-                                        start.y,
                             );
                             update_bounds(
-                                        &mut min_x, &mut max_x, &mut min_y, &mut max_y, end.x,
+                                &mut min_x, &mut max_x, &mut min_y, &mut max_y, end.x, end.y,
-                                        end.y,
                             );
                             let line = Line::new()
                                 .set("x1", start.x)
                                 .set("y1", start.y)
                                 .set("x2", end.x)
                                 .set("y2", end.y)
-                                        .set("stroke", color_to_svg(source.color))
+                                .set("stroke", color_to_svg(*color))
-                                        .set("stroke-width", source.pen_width);
+                                .set("stroke-width", *pen_width);
                             doc = doc.add(line);
                         }
-                                TurtleCommand::Circle {
+
+                        SvgRecord::Arc {
+                            start_position,
+                            start_heading,
                             radius,
                             angle,
                             direction,
-                                    ..
+                            color,
+                            pen_width,
                         } => {
                             use crate::circle_geometry::CircleGeometry;
+                            use crate::general::Radians;
                             let geom = CircleGeometry::new(
-                                        source.start_position,
+                                *start_position,
-                                        source.start_heading,
+                                Radians::new(*start_heading),
                                 *radius,
                                 *direction,
                             );
                             let center = geom.center;
-                                    if (*angle - 360.0).abs() < 1e-3 {
+                            // Include the bounding box of the full circle so partial arcs
-                                        // Voller Kreis
+                            // are never clipped.
                             update_bounds(
                                 &mut min_x,
                                 &mut max_x,
@@ -94,67 +96,55 @@ pub mod svg_export {
                                 center.x + radius,
                                 center.y + radius,
                             );
+
+                            if (angle.value() - 360.0).abs() < 1e-3 {
+                                // Full circle — emit as <circle>
                                 let circle = Circle::new()
                                     .set("cx", center.x)
                                     .set("cy", center.y)
                                     .set("r", *radius)
-                                            .set("stroke", color_to_svg(source.color))
+                                    .set("stroke", color_to_svg(*color))
-                                            .set("stroke-width", source.pen_width)
+                                    .set("stroke-width", *pen_width)
                                     .set("fill", "none");
                                 doc = doc.add(circle);
                             } else {
-                                        // Kreisbogen als <path>
+                                // Partial arc — emit as <path A …>
-                                        let start = source.start_position;
+                                let end = geom.position_at_angle(angle.as_radians().value());
-                                        let end = source.end_position;
+                                let large_arc = if angle.value() > 180.0 { 1 } else { 0 };
-                                        // For arcs, include the full circle bounds to ensure complete visibility
-                                        update_bounds(
-                                            &mut min_x,
-                                            &mut max_x,
-                                            &mut min_y,
-                                            &mut max_y,
-                                            center.x - radius,
-                                            center.y - radius,
-                                        );
-                                        update_bounds(
-                                            &mut min_x,
-                                            &mut max_x,
-                                            &mut min_y,
-                                            &mut max_y,
-                                            center.x + radius,
-                                            center.y + radius,
-                                        );
-                                        let large_arc = if *angle > 180.0 { 1 } else { 0 };
                                 let sweep = match direction {
                                     crate::circle_geometry::CircleDirection::Left => 0,
                                     crate::circle_geometry::CircleDirection::Right => 1,
                                 };
                                 let d = format!(
                                     "M {} {} A {} {} 0 {} {} {} {}",
-                                            start.x,
+                                    start_position.x,
-                                            start.y,
+                                    start_position.y,
                                     radius,
                                     radius,
                                     large_arc,
                                     sweep,
                                     end.x,
-                                            end.y
+                                    end.y,
                                 );
                                 let path = svg::node::element::Path::new()
                                     .set("d", d)
-                                            .set("stroke", color_to_svg(source.color))
+                                    .set("stroke", color_to_svg(*color))
-                                            .set("stroke-width", source.pen_width)
+                                    .set("stroke-width", *pen_width)
                                     .set("fill", "none");
                                 doc = doc.add(path);
                             }
                         }
-                                TurtleCommand::EndFill => {
+
-                                    // Fills werden als <path> mit Konturen ausgegeben
+                        SvgRecord::Fill {
-                                    if let Some(contours) = &source.contours {
+                            contours,
+                            fill_color,
+                            stroke_color,
+                        } => {
                             for contour in contours {
                                 for point in contour {
                                     update_bounds(
-                                                    &mut min_x, &mut max_x, &mut min_y, &mut max_y,
+                                        &mut min_x, &mut max_x, &mut min_y, &mut max_y, point.x,
-                                                    point.x, point.y,
+                                        point.y,
                                     );
                                 }
                             }
@@ -164,15 +154,9 @@ pub mod svg_export {
                                     if i > 0 {
                                         d.push(' ');
                                     }
-                                                d.push_str(&format!(
+                                    d.push_str(&format!("M {} {}", contour[0].x, contour[0].y));
-                                                    "M {} {}",
-                                                    contour[0].x, contour[0].y
-                                                ));
                                     for point in contour.iter().skip(1) {
-                                                    d.push_str(&format!(
+                                        d.push_str(&format!(" L {} {}", point.x, point.y));
-                                                        " L {} {}",
-                                                        point.x, point.y
-                                                    ));
                                     }
                                     d.push_str(" Z");
                                 }
@@ -180,63 +164,17 @@ pub mod svg_export {
                             if !d.is_empty() {
                                 let path = svg::node::element::Path::new()
                                     .set("d", d)
-                                                .set("fill", color_to_svg(source.fill_color))
+                                    .set("fill", color_to_svg(*fill_color))
                                     .set("fill-rule", "evenodd")
-                                                .set("stroke", color_to_svg(source.color));
+                                    .set("stroke", color_to_svg(*stroke_color));
                                 doc = doc.add(path);
                             }
-                                    } else {
-                                        // Fallback: Dummy-Polygon
-                                        update_bounds(
-                                            &mut min_x,
-                                            &mut max_x,
-                                            &mut min_y,
-                                            &mut max_y,
-                                            source.start_position.x,
-                                            source.start_position.y,
-                                        );
-                                        update_bounds(
-                                            &mut min_x,
-                                            &mut max_x,
-                                            &mut min_y,
-                                            &mut max_y,
-                                            source.start_position.x + 10.0,
-                                            source.start_position.y + 10.0,
-                                        );
-                                        update_bounds(
-                                            &mut min_x,
-                                            &mut max_x,
-                                            &mut min_y,
-                                            &mut max_y,
-                                            source.start_position.x + 5.0,
-                                            source.start_position.y + 15.0,
-                                        );
-                                        let poly = Polygon::new()
-                                            .set(
-                                                "points",
-                                                format!(
-                                                    "{},{} {},{} {},{}",
-                                                    source.start_position.x,
-                                                    source.start_position.y,
-                                                    source.start_position.x + 10.0,
-                                                    source.start_position.y + 10.0,
-                                                    source.start_position.x + 5.0,
-                                                    source.start_position.y + 15.0
-                                                ),
-                                            )
-                                            .set("fill", color_to_svg(source.fill_color))
-                                            .set("stroke", color_to_svg(source.color));
-                                        doc = doc.add(poly);
                         }
-                                }
+
-                                _ => {}
+                        SvgRecord::Text {
-                            }
-                        }
-                        DrawCommand::Text {
                             text,
                             position,
-                            source,
+                            color,
-                            ..
                         } => {
                             update_bounds(
                                 &mut min_x, &mut max_x, &mut min_y, &mut max_y, position.x,
@@ -245,7 +183,7 @@ pub mod svg_export {
                             let txt = SvgText::new()
                                 .set("x", position.x)
                                 .set("y", position.y)
-                                .set("fill", color_to_svg(source.color))
+                                .set("fill", color_to_svg(*color))
                                 .add(svg::node::Text::new(text.clone()));
                             doc = doc.add(txt);
                         }
@@ -260,7 +198,6 @@ pub mod svg_export {
                 let view_box = format!("{} {} {} {}", min_x - 20.0, min_y - 20.0, width, height);
                 doc = doc.set("viewBox", view_box);
             } else {
-                // Default viewBox if no elements
                 doc = doc.set("viewBox", "0 0 400 400");
             }
 

turtle-lib/src/general.rs

@@ -6,7 +6,7 @@ pub mod angle;
 pub mod fontsize;
 pub mod length;
 
-pub use angle::Angle;
+pub use angle::{Degrees, Radians};
 pub use fontsize::FontSize;
 pub use length::Length;
 

turtle-lib/src/general/angle.rs

@@ -1,205 +1,162 @@
-//! Angle type with degrees and radians support
+//! Angle unit newtypes: `Degrees` and `Radians`.
+//!
+//! ## Design
+//!
+//! Two separate types instead of a single enum so that function signatures are
+//! self-documenting and the compiler rejects wrong-unit arguments.
+//!
+//! - **`Degrees`** — public API boundary. Builder methods and `TurtleCommand`
+//!   fields that originate from user input store this type. Convert with
+//!   `as_radians()` before entering the rendering pipeline.
+//!
+//! - **`Radians`** — internal pipeline. All geometry functions and
+//!   `TurtleParams` arithmetic work in radians. Extract the raw `f32` with
+//!   `value()` only where stdlib trig functions (`sin`, `cos`, …) require it.
+//!
+//! There is intentionally **no** conversion from `Radians` back to `f32` that
+//! strips the unit tag silently — use `.value()` explicitly and at the last
+//! possible moment.
 
 use super::Precision;
-use std::ops::{Add, Div, Mul, Neg, Rem, Sub};
+use std::ops::Neg;
 
-#[derive(Copy, Clone, Debug, PartialEq)]
+/// An angle measured in degrees.
-pub enum AngleUnit {
+///
-    Degrees(Precision),
+/// Used at the public API boundary. Convert to [`Radians`] with `as_radians()`
-    Radians(Precision),
+/// before passing into internal rendering functions.
-}
+#[derive(Copy, Clone, Debug, PartialEq, PartialOrd, Default)]
+pub struct Degrees(pub Precision);
 
-impl Default for AngleUnit {
+impl Degrees {
-    fn default() -> Self {
+    /// Construct from a raw degrees value.
-        Self::Degrees(0.0)
+    #[must_use]
+    pub fn new(v: Precision) -> Self {
+        Self(v)
+    }
+
+    /// Convert to [`Radians`] for use in the rendering pipeline.
+    ///
+    /// This is the **only** correct way to enter the internal math layer.
+    #[must_use]
+    pub fn as_radians(self) -> Radians {
+        Radians(self.0.to_radians())
+    }
+
+    /// The raw degrees value.
+    ///
+    /// Use only for degree-to-degree arithmetic (e.g. negating a turn angle
+    /// before storing it as a command). Do not pass this to trig functions.
+    #[must_use]
+    pub fn value(self) -> Precision {
+        self.0
     }
 }
 
-#[derive(Copy, Clone, Debug, PartialEq)]
+impl Neg for Degrees {
-pub struct Angle {
-    value: AngleUnit,
-}
-
-impl Default for Angle {
-    fn default() -> Self {
-        Self {
-            value: AngleUnit::Degrees(0.0),
-        }
-    }
-}
-
-impl From<i16> for Angle {
-    fn from(i: i16) -> Self {
-        Self {
-            value: AngleUnit::Degrees(Precision::from(i)),
-        }
-    }
-}
-
-impl From<f32> for Angle {
-    fn from(f: f32) -> Self {
-        Self {
-            value: AngleUnit::Degrees(f),
-        }
-    }
-}
-
-impl Rem<Precision> for Angle {
     type Output = Self;
-
+    fn neg(self) -> Self {
-    fn rem(self, rhs: Precision) -> Self::Output {
+        Self(-self.0)
-        match self.value {
-            AngleUnit::Degrees(v) => Self::degrees(v % rhs),
-            AngleUnit::Radians(v) => Self::radians(v % rhs),
-        }
     }
 }
 
-impl Mul<Precision> for Angle {
+impl From<f32> for Degrees {
+    fn from(v: f32) -> Self {
+        Self(v)
+    }
+}
+
+impl From<i32> for Degrees {
+    fn from(v: i32) -> Self {
+        Self(v as Precision)
+    }
+}
+
+impl From<i16> for Degrees {
+    fn from(v: i16) -> Self {
+        Self(Precision::from(v))
+    }
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+
+/// An angle measured in radians.
+///
+/// Used in all internal function signatures and geometry math.  Extract the
+/// raw `f32` with [`value()`](Radians::value) only when calling stdlib trig
+/// functions (`sin`, `cos`, etc.).
+#[derive(Copy, Clone, Debug, PartialEq, PartialOrd, Default)]
+pub struct Radians(pub Precision);
+
+impl Radians {
+    /// Construct from a raw radians value.
+    #[must_use]
+    pub fn new(v: Precision) -> Self {
+        Self(v)
+    }
+
+    /// Convert to [`Degrees`] for display or user-facing output.
+    #[must_use]
+    pub fn as_degrees(self) -> Degrees {
+        Degrees(self.0.to_degrees())
+    }
+
+    /// The raw radians value.
+    ///
+    /// Use only when calling stdlib trig functions or other `f32`-based
+    /// math APIs. Keep `Radians` as the type at all internal function
+    /// boundaries.
+    #[must_use]
+    pub fn value(self) -> Precision {
+        self.0
+    }
+}
+
+impl Neg for Radians {
     type Output = Self;
-
+    fn neg(self) -> Self {
-    fn mul(self, rhs: Precision) -> Self::Output {
+        Self(-self.0)
-        match self.value {
-            AngleUnit::Degrees(v) => Self::degrees(v * rhs),
-            AngleUnit::Radians(v) => Self::radians(v * rhs),
-        }
     }
 }
 
-impl Div<Precision> for Angle {
+impl From<f32> for Radians {
-    type Output = Self;
+    fn from(v: f32) -> Self {
-
+        Self(v)
-    fn div(self, rhs: Precision) -> Self::Output {
-        match self.value {
-            AngleUnit::Degrees(v) => Self::degrees(v / rhs),
-            AngleUnit::Radians(v) => Self::radians(v / rhs),
-        }
-    }
-}
-
-impl Neg for Angle {
-    type Output = Self;
-
-    fn neg(self) -> Self::Output {
-        match self.value {
-            AngleUnit::Degrees(v) => Self::degrees(-v),
-            AngleUnit::Radians(v) => Self::radians(-v),
-        }
-    }
-}
-
-impl Neg for &Angle {
-    type Output = Angle;
-
-    fn neg(self) -> Self::Output {
-        match self.value {
-            AngleUnit::Degrees(v) => Angle::degrees(-v),
-            AngleUnit::Radians(v) => Angle::radians(-v),
-        }
-    }
-}
-
-impl Add for Angle {
-    type Output = Angle;
-
-    fn add(self, rhs: Self) -> Self::Output {
-        match (self.value, rhs.value) {
-            (AngleUnit::Degrees(v), AngleUnit::Degrees(o)) => Self::degrees(v + o),
-            (AngleUnit::Degrees(v), AngleUnit::Radians(o)) => Self::radians(v.to_radians() + o),
-            (AngleUnit::Radians(v), AngleUnit::Degrees(o)) => Self::radians(v + o.to_radians()),
-            (AngleUnit::Radians(v), AngleUnit::Radians(o)) => Self::radians(v + o),
-        }
-    }
-}
-
-impl Sub for Angle {
-    type Output = Angle;
-
-    fn sub(self, rhs: Self) -> Self::Output {
-        match (self.value, rhs.value) {
-            (AngleUnit::Degrees(v), AngleUnit::Degrees(o)) => Self::degrees(v - o),
-            (AngleUnit::Degrees(v), AngleUnit::Radians(o)) => Self::radians(v.to_radians() - o),
-            (AngleUnit::Radians(v), AngleUnit::Degrees(o)) => Self::radians(v - o.to_radians()),
-            (AngleUnit::Radians(v), AngleUnit::Radians(o)) => Self::radians(v - o),
-        }
-    }
-}
-
-impl Angle {
-    #[must_use]
-    pub fn degrees(value: Precision) -> Self {
-        Self {
-            value: AngleUnit::Degrees(value),
-        }
-    }
-
-    #[must_use]
-    pub fn radians(value: Precision) -> Self {
-        Self {
-            value: AngleUnit::Radians(value),
-        }
-    }
-
-    #[must_use]
-    pub fn value(&self) -> Precision {
-        match self.value {
-            AngleUnit::Degrees(v) | AngleUnit::Radians(v) => v,
-        }
-    }
-
-    #[must_use]
-    pub fn to_radians(self) -> Self {
-        match self.value {
-            AngleUnit::Degrees(v) => Self::radians(v.to_radians()),
-            AngleUnit::Radians(_) => self,
-        }
-    }
-
-    #[must_use]
-    pub fn to_degrees(self) -> Self {
-        match self.value {
-            AngleUnit::Degrees(_) => self,
-            AngleUnit::Radians(v) => Self::degrees(v.to_degrees()),
-        }
-    }
-
-    #[must_use]
-    pub fn limit_smaller_than_full_circle(self) -> Self {
-        use std::f32::consts::PI;
-        match self.value {
-            AngleUnit::Degrees(v) => Self::degrees(v % 360.0),
-            AngleUnit::Radians(v) => Self::radians(v % (2.0 * PI)),
-        }
     }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
+    use std::f32::consts::PI;
 
     #[test]
-    fn convert_to_radians() {
+    fn degrees_to_radians_roundtrip() {
-        let radi = Angle::radians(30f32.to_radians());
+        let deg = Degrees::new(180.0);
-        let degr = Angle::degrees(30f32);
+        let rad = deg.as_radians();
-        let converted = degr.to_radians();
+        assert!(
-        assert!((radi.value() - converted.value()).abs() < 0.0001);
+            (rad.value() - PI).abs() < 1e-6,
+            "expected π, got {}",
+            rad.value()
+        );
+        let back = rad.as_degrees();
+        assert!(
+            (back.value() - 180.0).abs() < 1e-4,
+            "expected 180°, got {}",
+            back.value()
+        );
     }
 
     #[test]
-    fn sum_degrees() {
+    fn negation() {
-        let fst = Angle::degrees(30f32);
+        assert_eq!(-Degrees::new(90.0), Degrees::new(-90.0));
-        let snd = Angle::degrees(30f32);
+        assert_eq!(-Radians::new(1.0), Radians::new(-1.0));
-        let sum = fst + snd;
-        assert!((sum.value() - 60f32).abs() < 0.0001);
-        assert!((sum.to_radians().value() - 60f32.to_radians()).abs() < 0.0001);
     }
 
     #[test]
-    fn sum_mixed() {
+    fn from_integer() {
-        let fst = Angle::degrees(30f32);
+        let d: Degrees = 90_i32.into();
-        let snd = Angle::radians(30f32.to_radians());
+        assert_eq!(d, Degrees::new(90.0));
-        let sum = fst + snd;
+        let d2: Degrees = 45_i16.into();
-        assert!((sum.to_degrees().value() - 60f32).abs() < 0.0001);
+        assert_eq!(d2, Degrees::new(45.0));
-        assert!((sum.to_radians().value() - 60f32.to_radians()).abs() < 0.0001);
     }
 }

turtle-lib/src/lib.rs

@@ -46,30 +46,29 @@
 //! }
 //! ```
 
-pub mod builders;
+pub(crate) mod builders;
-pub mod circle_geometry;
+pub(crate) mod circle_geometry;
-pub mod commands;
+pub(crate) mod command_behavior;
-pub mod commands_channel;
+pub(crate) mod commands;
-pub mod drawing;
+pub(crate) mod commands_channel;
-pub mod execution;
+pub(crate) mod drawing;
-pub mod general;
+pub(crate) mod execution;
-pub mod shapes;
+pub(crate) mod general;
-pub mod state;
+pub(crate) mod shapes;
-pub mod tessellation;
+pub(crate) mod state;
-pub mod tweening;
+pub(crate) mod tessellation;
+pub(crate) mod tweening;
 
 // Re-export commonly used types
 pub use builders::{CurvedMovement, DirectionalMovement, Turnable, TurtlePlan, WithCommands};
 pub use commands::{CommandQueue, TurtleCommand};
-pub use commands_channel::{turtle_command_channel, TurtleCommandReceiver, TurtleCommandSender};
+pub use commands_channel::TurtleCommandSender;
-pub use general::{Angle, AnimationSpeed, Color, Coordinate, Length, Precision};
+pub use general::{AnimationSpeed, Color, Coordinate, Degrees, Length, Precision, Radians};
 pub use shapes::{ShapeType, TurtleShape};
-pub use state::{DrawCommand, Turtle, TurtleWorld};
-pub use tweening::TweenController;
 
 pub mod export;
 #[cfg(feature = "svg")]
-pub mod export_svg;
+pub(crate) mod export_svg;
 
 // Re-export the turtle_main macro
 pub use turtle_lib_macros::turtle_main;
@@ -79,6 +78,8 @@ pub use macroquad::prelude::{
     vec2, BLACK, BLUE, DARKGRAY, GOLD, GREEN, ORANGE, PURPLE, RED, WHITE, YELLOW,
 };
 
+use crate::commands_channel::TurtleCommandReceiver;
+use crate::state::TurtleWorld;
 use macroquad::prelude::*;
 use std::collections::HashMap;
 
@@ -95,9 +96,7 @@ pub struct TurtleApp {
 }
 
 impl TurtleApp {
-    /// Exportiere das aktuelle Drawing in das gewünschte Format
+    /// Export the current drawing to a file in the specified format.
-    #[allow(unused_variables)]
-    /// Export the current drawing to a file in the specified format
     ///
     /// # Errors
     ///
@@ -115,10 +114,10 @@ impl TurtleApp {
                 let exporter = SvgExporter;
                 exporter.export(&self.world, filename)
             }
-            // Weitere Formate können hier ergänzt werden
+            // Additional formats can be registered here.
             #[allow(unreachable_patterns)]
             _ => Err(export::ExportError::Format(
-                "Export-Format nicht unterstützt".to_string(),
+                "Unsupported export format".to_string(),
             )),
         }
     }
@@ -290,20 +289,25 @@ impl TurtleApp {
 
         // Update all turtles' tween controllers
         for turtle in &mut self.world.turtles {
-            // Extract draw_commands and controller temporarily to avoid borrow conflicts
+            // Drive this turtle's animation controller for one frame.
-
+            // `update_tweens` splits &mut Turtle into disjoint field borrows so
-            // Update the controller
+            // TweenController::update can be a proper &mut self method.
-            let completed_commands = TweenController::update(turtle);
+            let completed_commands = turtle.update_tweens();
 
             // Process all completed commands and add to the turtle's commands
-            for (completed_cmd, tween_start, mut end_state) in completed_commands {
+            for (completed_cmd, tween_start, end_state) in completed_commands {
-                let draw_command = execution::add_draw_for_completed_tween(
+                if let Some(draw_cmd) =
+                    execution::tessellate_command(&completed_cmd, &tween_start, end_state.position)
+                {
+                    #[cfg(feature = "svg")]
+                    execution::push_svg_for_draw(
                         &completed_cmd,
                         &tween_start,
-                    &mut end_state,
+                        end_state.position,
+                        &mut turtle.svg_log,
                     );
-                // Add the new draw commands to the turtle
+                    turtle.commands.push(draw_cmd);
-                turtle.commands.extend(draw_command);
+                }
             }
         }
     }
@@ -367,14 +371,31 @@ impl TurtleApp {
             .all(|turtle| turtle.tween_controller.is_complete())
     }
 
+    /// Check if all animations are complete (alias for is_complete)
+    #[must_use]
+    pub fn all_animations_complete(&self) -> bool {
+        self.is_complete()
+    }
+
+    /// Set the animation speed for all turtles
+    ///
+    /// # Arguments
+    /// * `speed` - The animation speed to set for all turtles
+    pub fn set_all_turtles_speed(&mut self, speed: AnimationSpeed) {
+        for turtle in &mut self.world.turtles {
+            turtle.set_speed(speed);
+            turtle.tween_controller.set_speed(speed);
+        }
+    }
+
     /// Get reference to the world state
     #[must_use]
-    pub fn world(&self) -> &TurtleWorld {
+    pub(crate) fn world(&self) -> &TurtleWorld {
         &self.world
     }
 
     /// Get mutable reference to the world state
-    pub fn world_mut(&mut self) -> &mut TurtleWorld {
+    pub(crate) fn world_mut(&mut self) -> &mut TurtleWorld {
         &mut self.world
     }
 }

turtle-lib/src/state.rs

@@ -1,40 +1,40 @@
 //! Turtle state and world state management
 
 use crate::commands::CommandQueue;
-use crate::general::{Angle, AnimationSpeed, Color, Coordinate};
+use crate::general::{AnimationSpeed, Color, Coordinate};
 use crate::shapes::TurtleShape;
 use crate::tweening::TweenController;
 use macroquad::prelude::*;
 
 /// State during active fill operation
 #[derive(Clone, Debug)]
-pub struct FillState {
+pub(crate) struct FillState {
     /// Starting position of the fill
-    pub start_position: Coordinate,
+    pub(crate) start_position: Coordinate,
 
     /// All contours collected so far. Each contour is a separate closed path.
     /// The first contour is the outer boundary, subsequent contours are holes.
-    pub contours: Vec<Vec<Coordinate>>,
+    pub(crate) contours: Vec<Vec<Coordinate>>,
 
     /// Current contour being built (vertices for the active `pen_down` segment)
-    pub current_contour: Vec<Coordinate>,
+    pub(crate) current_contour: Vec<Coordinate>,
 
     /// Fill color (cached from when `begin_fill` was called)
-    pub fill_color: Color,
+    pub(crate) fill_color: Color,
 }
 
 /// Parameters that define a turtle's visual state
 #[derive(Clone, Debug)]
-pub struct TurtleParams {
+pub(crate) struct TurtleParams {
-    pub position: Vec2,
+    pub(crate) position: Vec2,
-    pub heading: f32,
+    pub(crate) heading: f32,
-    pub pen_down: bool,
+    pub(crate) pen_down: bool,
-    pub pen_width: f32,
+    pub(crate) pen_width: f32,
-    pub color: Color,
+    pub(crate) color: Color,
-    pub fill_color: Option<Color>,
+    pub(crate) fill_color: Option<Color>,
-    pub visible: bool,
+    pub(crate) visible: bool,
-    pub shape: crate::shapes::TurtleShape,
+    pub(crate) shape: crate::shapes::TurtleShape,
-    pub speed: AnimationSpeed,
+    pub(crate) speed: AnimationSpeed,
 }
 
 impl Default for TurtleParams {
@@ -56,18 +56,21 @@ impl Default for TurtleParams {
 
 /// State of a single turtle
 #[derive(Clone, Debug)]
-pub struct Turtle {
+pub(crate) struct Turtle {
-    pub turtle_id: usize,
+    pub(crate) turtle_id: usize,
-    pub params: TurtleParams,
+    pub(crate) params: TurtleParams,
 
     // Fill tracking
-    pub filling: Option<FillState>,
+    pub(crate) filling: Option<FillState>,
 
     // Drawing commands created by this turtle
-    pub commands: Vec<DrawCommand>,
+    pub(crate) commands: Vec<DrawCommand>,
+
+    // SVG draw-event log — populated alongside `commands`, consumed by the SVG exporter
+    pub(crate) svg_log: SvgLog,
 
     // Animation controller for this turtle
-    pub tween_controller: TweenController,
+    pub(crate) tween_controller: TweenController,
 }
 
 impl Default for Turtle {
@@ -77,6 +80,7 @@ impl Default for Turtle {
             params: TurtleParams::default(),
             filling: None,
             commands: Vec::new(),
+            svg_log: SvgLog::default(),
             tween_controller: TweenController::new(CommandQueue::new(), AnimationSpeed::default()),
         }
     }
@@ -88,14 +92,15 @@ impl Turtle {
     }
 
     #[must_use]
-    pub fn heading_angle(&self) -> Angle {
+    pub fn heading_angle(&self) -> crate::general::Radians {
-        Angle::radians(self.params.heading)
+        crate::general::Radians::new(self.params.heading)
     }
 
     /// Reset turtle to default state (preserves `turtle_id` and queued commands)
     pub fn reset(&mut self) {
         // Clear all drawings
         self.commands.clear();
+        self.svg_log.clear();
 
         // Clear fill state
         self.filling = None;
@@ -106,6 +111,27 @@ impl Turtle {
         // Keep turtle_id and tween_controller (preserves queued commands)
     }
 
+    /// Drive the animation controller for one frame.
+    ///
+    /// Returns `(command, start_params, end_params)` for every command that
+    /// completed this frame and whose stroke needs to be tessellated by the
+    /// caller into a `DrawCommand`.
+    ///
+    /// This method performs the correct disjoint field-borrow split so that
+    /// `TweenController::update` can be a proper `&mut self` method instead
+    /// of the old static-method borrow-checker workaround.
+    pub fn update_tweens(
+        &mut self,
+    ) -> Vec<(crate::commands::TurtleCommand, TurtleParams, TurtleParams)> {
+        self.tween_controller.update(
+            self.turtle_id,
+            &mut self.params,
+            &mut self.filling,
+            &mut self.commands,
+            &mut self.svg_log,
+        )
+    }
+
     /// Start recording fill vertices
     pub fn begin_fill(&mut self, fill_color: Color) {
         self.filling = Some(FillState {
@@ -257,11 +283,75 @@ impl Turtle {
     }
 }
 
+/// The draw-event log for SVG export.
+///
+/// When the `svg` feature is **disabled** this is a zero-sized type (ZST) with
+/// no fields — it compiles away entirely and adds zero overhead to `Turtle`.
+/// When the feature is **enabled** it owns a `Vec<SvgRecord>` that the SVG
+/// exporter consumes after rendering.
+///
+/// All methods are always callable so function signatures that accept
+/// `&mut SvgLog` need no feature-gating at the parameter level.
+#[derive(Clone, Debug, Default)]
+pub(crate) struct SvgLog {
+    #[cfg(feature = "svg")]
+    pub(crate) records: Vec<SvgRecord>,
+}
+
+impl SvgLog {
+    pub(crate) fn clear(&mut self) {
+        #[cfg(feature = "svg")]
+        self.records.clear();
+    }
+
+    #[cfg(feature = "svg")]
+    pub(crate) fn push(&mut self, record: SvgRecord) {
+        self.records.push(record);
+    }
+}
+
+/// A drawing event captured for SVG export.
+///
+/// Only compiled when the `svg` feature is enabled.
+#[cfg(feature = "svg")]
+#[derive(Clone, Debug)]
+pub(crate) enum SvgRecord {
+    /// A straight-line stroke.
+    Line {
+        start: Vec2,
+        end: Vec2,
+        color: Color,
+        pen_width: f32,
+    },
+    /// An arc or full-circle stroke.
+    Arc {
+        start_position: Vec2,
+        start_heading: f32,
+        radius: crate::general::Precision,
+        angle: crate::general::Degrees,
+        direction: crate::circle_geometry::CircleDirection,
+        color: Color,
+        pen_width: f32,
+    },
+    /// A filled region (potentially with holes via the even-odd rule).
+    Fill {
+        contours: Vec<Vec<crate::general::Coordinate>>,
+        fill_color: Color,
+        stroke_color: Color,
+    },
+    /// A text element.
+    Text {
+        text: String,
+        position: Vec2,
+        color: Color,
+    },
+}
+
 /// Cached mesh data that can be cloned and converted to Mesh when needed
 #[derive(Clone, Debug)]
-pub struct MeshData {
+pub(crate) struct MeshData {
-    pub vertices: Vec<macroquad::prelude::Vertex>,
+    pub(crate) vertices: Vec<macroquad::prelude::Vertex>,
-    pub indices: Vec<u16>,
+    pub(crate) indices: Vec<u16>,
 }
 
 impl MeshData {
@@ -275,44 +365,28 @@ impl MeshData {
     }
 }
 
-/// Drawable elements in the world
+/// Drawable elements in the world.
-/// All drawing is done via Lyon-tessellated meshes for consistency and quality
+/// All drawing is done via Lyon-tessellated meshes for consistency and quality.
 #[derive(Clone, Debug)]
-pub struct TurtleSource {
+pub(crate) enum DrawCommand {
-    pub command: crate::commands::TurtleCommand,
+    /// Pre-tessellated mesh data (lines, arcs, circles, polygons — all use this).
-    pub color: Color,
+    Mesh { data: MeshData },
-    pub fill_color: Color,
+    /// Text rendering command.
-    pub pen_width: f32,
-    pub start_position: Vec2,
-    pub end_position: Vec2,
-    pub start_heading: f32,
-    pub contours: Option<Vec<Vec<crate::general::Coordinate>>>,
-}
-
-#[derive(Clone, Debug)]
-pub enum DrawCommand {
-    /// Pre-tessellated mesh data (lines, arcs, circles, polygons - all use this)
-    Mesh {
-        data: MeshData,
-        source: TurtleSource,
-    },
-    /// Text rendering command
     Text {
         text: String,
         position: Vec2,
         heading: f32,
         font_size: crate::general::FontSize,
         color: Color,
-        source: TurtleSource,
     },
 }
 
 /// The complete turtle world containing all drawing state
-pub struct TurtleWorld {
+pub(crate) struct TurtleWorld {
     /// All turtles in the world (indexed by turtle ID)
-    pub turtles: Vec<Turtle>,
+    pub(crate) turtles: Vec<Turtle>,
-    pub camera: Camera2D,
+    pub(crate) camera: Camera2D,
-    pub background_color: Color,
+    pub(crate) background_color: Color,
 }
 
 impl TurtleWorld {

turtle-lib/src/tessellation.rs

@@ -14,26 +14,30 @@ use macroquad::prelude::*;
 
 /// Convert macroquad Vec2 to Lyon Point
 #[must_use]
-pub fn to_lyon_point(v: Vec2) -> Point {
+pub(crate) fn to_lyon_point(v: Vec2) -> Point {
     point(v.x, v.y)
 }
 
 /// Convert Lyon Point to macroquad Vec2
 #[allow(dead_code)]
 #[must_use]
-pub fn to_macroquad_vec2(p: Point) -> Vec2 {
+pub(crate) fn to_macroquad_vec2(p: Point) -> Vec2 {
     vec2(p.x, p.y)
 }
 
 /// Simple vertex type for Lyon tessellation
 #[derive(Copy, Clone, Debug)]
-pub struct SimpleVertex {
+pub(crate) struct SimpleVertex {
-    pub position: [f32; 2],
+    pub(crate) position: [f32; 2],
 }
 
 /// Build mesh data from Lyon tessellation
 #[must_use]
-pub fn build_mesh_data(vertices: &[SimpleVertex], indices: &[u16], color: Color) -> MeshData {
+pub(crate) fn build_mesh_data(
+    vertices: &[SimpleVertex],
+    indices: &[u16],
+    color: Color,
+) -> MeshData {
     let verts: Vec<Vertex> = vertices
         .iter()
         .map(|v| Vertex {
@@ -62,7 +66,7 @@ pub fn build_mesh_data(vertices: &[SimpleVertex], indices: &[u16], color: Color)
 /// # Errors
 ///
 /// Returns an error if no vertices are provided or if tessellation fails.
-pub fn tessellate_polygon(
+pub(crate) fn tessellate_polygon(
     vertices: &[Vec2],
     color: Color,
 ) -> Result<MeshData, Box<dyn std::error::Error>> {
@@ -107,7 +111,7 @@ pub fn tessellate_polygon(
 /// # Errors
 ///
 /// Returns an error if no contours are provided or if tessellation fails.
-pub fn tessellate_multi_contour(
+pub(crate) fn tessellate_multi_contour(
     contours: &[Vec<Vec2>],
     color: Color,
 ) -> Result<MeshData, Box<dyn std::error::Error>> {
@@ -203,7 +207,7 @@ pub fn tessellate_multi_contour(
 /// # Errors
 ///
 /// Returns an error if no vertices are provided or if tessellation fails.
-pub fn tessellate_stroke(
+pub(crate) fn tessellate_stroke(
     vertices: &[Vec2],
     color: Color,
     width: f32,
@@ -249,7 +253,7 @@ pub fn tessellate_stroke(
 /// # Errors
 ///
 /// Returns an error if tessellation fails.
-pub fn tessellate_circle(
+pub(crate) fn tessellate_circle(
     center: Vec2,
     radius: f32,
     color: Color,
@@ -295,7 +299,7 @@ pub fn tessellate_circle(
 ///
 /// Returns an error if tessellation fails.
 #[allow(clippy::too_many_arguments)]
-pub fn tessellate_arc(
+pub(crate) fn tessellate_arc(
     center: Vec2,
     radius: f32,
     start_angle_degrees: f32,
@@ -305,40 +309,32 @@ pub fn tessellate_arc(
     segments: usize,
     direction: crate::circle_geometry::CircleDirection,
 ) -> Result<MeshData, Box<dyn std::error::Error>> {
-    // Build arc path manually from segments
+    use crate::circle_geometry::arc_points;
-    let mut builder = Path::builder();
 
     let start_angle = start_angle_degrees.to_radians();
-    let arc_angle = arc_angle_degrees.to_radians();
+    let sweep_angle = arc_angle_degrees.to_radians();
-    let step = arc_angle / segments as f32;
 
-    // Calculate first point
+    let mut builder = Path::builder();
-    let first_point = point(
+
+    // Start point of the arc (arc_points returns everything *after* this)
+    builder.begin(point(
         center.x + radius * start_angle.cos(),
         center.y + radius * start_angle.sin(),
-    );
+    ));
-    builder.begin(first_point);
 
-    // Add remaining points - direction matters!
+    // Remaining points — single source of truth for arc sampling
-    for i in 1..=segments {
+    for pt in arc_points(
-        let angle = match direction {
+        center,
-            crate::circle_geometry::CircleDirection::Left => {
+        radius,
-                // Counter-clockwise: subtract angle
+        start_angle,
-                start_angle - step * i as f32
+        sweep_angle,
-            }
+        segments,
-            crate::circle_geometry::CircleDirection::Right => {
+        direction,
-                // Clockwise: add angle
+    ) {
-                start_angle + step * i as f32
+        builder.line_to(point(pt.x, pt.y));
-            }
-        };
-        let pt = point(
-            center.x + radius * angle.cos(),
-            center.y + radius * angle.sin(),
-        );
-        builder.line_to(pt);
     }
 
-    builder.end(false); // Don't close the arc
+    builder.end(false); // open arc, not a closed polygon
     let path = builder.build();
 
     // Tessellate stroke

turtle-lib/src/tweening.rs

@@ -2,8 +2,8 @@
 
 use crate::circle_geometry::{CircleDirection, CircleGeometry};
 use crate::commands::{CommandQueue, TurtleCommand};
-use crate::general::AnimationSpeed;
+use crate::general::{AnimationSpeed, Radians};
-use crate::state::{Turtle, TurtleParams};
+use crate::state::{DrawCommand, FillState, TurtleParams};
 use macroquad::prelude::*;
 use tween::{CubicInOut, TweenValue, Tweener};
 
@@ -45,22 +45,26 @@ impl From<TweenVec2> for Vec2 {
 
 /// Controls tweening of turtle commands
 #[derive(Clone, Debug, Default)]
-pub struct TweenController {
+pub(crate) struct TweenController {
     queue: CommandQueue,
+    /// Cursor into `queue` — tracks which command executes next.
+    /// Lives here, not in `CommandQueue`, so that cloning or appending to the
+    /// queue never silently resets or mid-stream-shifts the execution position.
+    cursor: usize,
     current_tween: Option<CommandTween>,
     speed: AnimationSpeed,
 }
 
 #[derive(Clone, Debug)]
-pub struct CommandTween {
+pub(crate) struct CommandTween {
-    pub turtle_id: usize,
+    pub(crate) turtle_id: usize,
-    pub command: TurtleCommand,
+    pub(crate) command: TurtleCommand,
-    pub start_time: f64,
+    pub(crate) start_time: f64,
-    pub duration: f64,
+    pub(crate) duration: f64,
-    pub start_params: TurtleParams,
+    pub(crate) start_params: TurtleParams,
-    pub target_params: TurtleParams,
+    pub(crate) target_params: TurtleParams,
-    pub current_position: Vec2,
+    pub(crate) current_position: Vec2,
-    pub current_heading: f32,
+    pub(crate) current_heading: f32,
     position_tweener: Tweener<TweenVec2, f64, CubicInOut>,
     heading_tweener: Tweener<f32, f64, CubicInOut>,
     pen_width_tweener: Tweener<f32, f64, CubicInOut>,
@@ -71,6 +75,7 @@ impl TweenController {
     pub fn new(queue: CommandQueue, speed: AnimationSpeed) -> Self {
         Self {
             queue,
+            cursor: 0,
             current_tween: None,
             speed,
         }
@@ -80,51 +85,72 @@ impl TweenController {
         self.speed = speed;
     }
 
-    /// Append commands to the queue
+    /// Append commands to the queue.
+    ///
+    /// The cursor is **not** reset — commands already consumed remain consumed,
+    /// and the new commands are picked up naturally as the cursor advances.
     pub fn append_commands(&mut self, new_queue: CommandQueue) {
         self.queue.extend(new_queue);
     }
 
-    /// Update the tween, returns `Vec` of (`command`, `start_state`, `end_state`) for all completed commands this frame
+    /// Drive the animation controller for one frame.
-    /// Also takes commands vec to handle side effects like fill operations
+    ///
-    /// Each `command` has its own `start_state` and `end_state` pair
+    /// Returns `(command, start_params, end_params)` for every command that
+    /// completed this frame and whose stroke needs to be tessellated by the
+    /// caller.
+    ///
+    /// By accepting `params`, `filling`, and `commands` as separate mutable
+    /// borrows the caller can split `&mut Turtle` into disjoint field borrows,
+    /// eliminating the old static-method borrow-checker workaround.
     #[allow(clippy::too_many_lines)]
-    pub fn update(state: &mut Turtle) -> Vec<(TurtleCommand, TurtleParams, TurtleParams)> {
+    pub fn update(
+        &mut self,
+        turtle_id: usize,
+        params: &mut TurtleParams,
+        filling: &mut Option<FillState>,
+        commands: &mut Vec<DrawCommand>,
+        svg_log: &mut crate::state::SvgLog,
+    ) -> Vec<(TurtleCommand, TurtleParams, TurtleParams)> {
         // In instant mode, execute commands up to the draw calls per frame limit
-        if let AnimationSpeed::Instant(max_draw_calls) = state.tween_controller.speed {
+        if let AnimationSpeed::Instant(max_draw_calls) = self.speed {
             let mut completed_commands: Vec<(TurtleCommand, TurtleParams, TurtleParams)> =
                 Vec::new();
             let mut draw_call_count = 0;
 
-            // Consume commands from the real queue so the current_index advances
+            // Advance cursor through the queue for each command consumed
-            while let Some(command) = state.tween_controller.queue.next() {
+            while let Some(command) = self.queue.get(self.cursor).cloned() {
+                self.cursor += 1;
                 // Handle SetSpeed command to potentially switch modes
                 if let TurtleCommand::SetSpeed(new_speed) = &command {
-                    state.params.speed = *new_speed;
+                    params.speed = *new_speed;
-                    state.tween_controller.speed = *new_speed;
+                    self.speed = *new_speed;
-                    if matches!(state.tween_controller.speed, AnimationSpeed::Animated(_)) {
+                    if matches!(self.speed, AnimationSpeed::Animated(_)) {
                         break;
                     }
                     continue;
                 }
 
                 // Execute side-effect-only commands using centralized helper
-                if crate::execution::execute_command_side_effects(&command, state) {
+                if crate::execution::execute_command_side_effects(
+                    &command, turtle_id, params, filling, commands, svg_log,
+                ) {
                     continue; // Command fully handled
                 }
 
                 // Save start state and compute target state
-                let start_params = state.params.clone();
+                let start_params = params.clone();
                 let target_params = Self::calculate_target_state(&start_params, &command);
 
                 // Update state to the target (instant execution)
-                state.params = target_params.clone();
+                *params = target_params.clone();
 
                 // Record fill vertices AFTER movement
                 crate::execution::record_fill_vertices_after_movement(
                     &command,
                     &start_params,
-                    state,
+                    turtle_id,
+                    params,
+                    filling,
                 );
 
                 // Collect drawable commands (return start and target so caller can create draw meshes)
@@ -141,7 +167,7 @@ impl TweenController {
         }
 
         // Process current tween
-        if let Some(ref mut tween) = state.tween_controller.current_tween {
+        if let Some(ref mut tween) = self.current_tween {
             let elapsed = get_time() - tween.start_time;
 
             // Use tweeners to calculate current values
@@ -155,10 +181,10 @@ impl TweenController {
                     direction,
                     ..
                 } => {
-                    let angle_traveled = angle.to_radians() * progress;
+                    let angle_traveled = angle.as_radians().value() * progress;
                     calculate_circle_position(
                         tween.start_params.position,
-                        tween.start_params.heading,
+                        Radians::new(tween.start_params.heading),
                         *radius,
                         angle_traveled,
                         *direction,
@@ -170,7 +196,7 @@ impl TweenController {
                 }
             };
 
-            state.params.position = current_position;
+            params.position = current_position;
             tween.current_position = current_position;
 
             // Heading changes proportionally with progress for all commands
@@ -179,14 +205,14 @@ impl TweenController {
                     angle, direction, ..
                 } => match direction {
                     CircleDirection::Left => {
-                        tween.start_params.heading - angle.to_radians() * progress
+                        tween.start_params.heading - angle.as_radians().value() * progress
                     }
                     CircleDirection::Right => {
-                        tween.start_params.heading + angle.to_radians() * progress
+                        tween.start_params.heading + angle.as_radians().value() * progress
                     }
                 },
                 TurtleCommand::Turn(angle) => {
-                    tween.start_params.heading + angle.to_radians() * progress
+                    tween.start_params.heading + angle.as_radians().value() * progress
                 }
                 _ => {
                     // For other commands that change heading, lerp directly
@@ -195,18 +221,18 @@ impl TweenController {
                 }
             });
 
-            state.params.heading = current_heading;
+            params.heading = current_heading;
             tween.current_heading = current_heading;
-            state.params.pen_width = tween.pen_width_tweener.move_to(elapsed);
+            params.pen_width = tween.pen_width_tweener.move_to(elapsed);
 
             // Discrete properties (switch at 50% progress)
             let progress = (elapsed / tween.duration).min(1.0);
             if progress >= 0.5 {
-                state.params.pen_down = tween.target_params.pen_down;
+                params.pen_down = tween.target_params.pen_down;
-                state.params.color = tween.target_params.color;
+                params.color = tween.target_params.color;
-                state.params.fill_color = tween.target_params.fill_color;
+                params.fill_color = tween.target_params.fill_color;
-                state.params.visible = tween.target_params.visible;
+                params.visible = tween.target_params.visible;
-                state.params.shape = tween.target_params.shape.clone();
+                params.shape = tween.target_params.shape.clone();
             }
 
             // Check if tween is finished (use heading_tweener as it's used by all commands)
@@ -215,20 +241,24 @@ impl TweenController {
                 let target_params = tween.target_params.clone();
                 let command = tween.command.clone();
 
-                // Drop the mutable borrow of tween before mutably borrowing state
+                // tween borrow ends here (NLL) — safe to reassign self.current_tween below
-                state.params = target_params.clone();
+                *params = target_params.clone();
 
                 crate::execution::record_fill_vertices_after_movement(
                     &command,
                     &start_params,
-                    state,
+                    turtle_id,
+                    params,
+                    filling,
                 );
 
-                state.tween_controller.current_tween = None;
+                self.current_tween = None;
 
                 // Execute side-effect-only commands using centralized helper
-                if crate::execution::execute_command_side_effects(&command, state) {
+                if crate::execution::execute_command_side_effects(
-                    return Self::update(state); // Continue to next command
+                    &command, turtle_id, params, filling, commands, svg_log,
+                ) {
+                    return self.update(turtle_id, params, filling, commands, svg_log);
                 }
 
                 // Return drawable commands using the original start and target params
@@ -236,43 +266,45 @@ impl TweenController {
                     return vec![(command, start_params.clone(), target_params.clone())];
                 }
 
-                return Self::update(state); // Continue to next command
+                return self.update(turtle_id, params, filling, commands, svg_log);
             }
 
             return Vec::new();
         }
 
         // Start next tween
-        if let Some(command) = state.tween_controller.queue.next() {
+        if let Some(command) = self.queue.get(self.cursor).cloned() {
-            let command_clone = command.clone();
+            self.cursor += 1;
 
             // Handle commands that should execute immediately (no animation)
-            match &command_clone {
+            match &command {
                 TurtleCommand::SetSpeed(new_speed) => {
-                    state.set_speed(*new_speed);
+                    params.speed = *new_speed;
-                    state.tween_controller.speed = *new_speed;
+                    self.speed = *new_speed;
-                    if matches!(state.tween_controller.speed, AnimationSpeed::Instant(_)) {
+                    if matches!(self.speed, AnimationSpeed::Instant(_)) {
-                        return Self::update(state);
+                        return self.update(turtle_id, params, filling, commands, svg_log);
                     }
-                    return Self::update(state);
+                    return self.update(turtle_id, params, filling, commands, svg_log);
                 }
                 _ => {
                     // Use centralized helper for side effects
-                    if crate::execution::execute_command_side_effects(&command_clone, state) {
+                    if crate::execution::execute_command_side_effects(
-                        return Self::update(state);
+                        &command, turtle_id, params, filling, commands, svg_log,
+                    ) {
+                        return self.update(turtle_id, params, filling, commands, svg_log);
                     }
                 }
             }
 
-            let speed = state.tween_controller.speed; // Extract speed before borrowing self
+            let speed = self.speed;
-            let duration = Self::calculate_duration_with_state(&command_clone, state, speed);
+            let duration = Self::calculate_duration_with_state(&command, params, speed);
 
             // Calculate target state
-            let target_state = Self::calculate_target_state(&state.params, &command_clone);
+            let target_state = Self::calculate_target_state(params, &command);
 
             // Create tweeners for smooth animation
             let position_tweener = Tweener::new(
-                TweenVec2::from(state.params.position),
+                TweenVec2::from(params.position),
                 TweenVec2::from(target_state.position),
                 duration,
                 CubicInOut,
@@ -284,21 +316,21 @@ impl TweenController {
             );
 
             let pen_width_tweener = Tweener::new(
-                state.params.pen_width,
+                params.pen_width,
                 target_state.pen_width,
                 duration,
                 CubicInOut,
             );
 
-            state.tween_controller.current_tween = Some(CommandTween {
+            self.current_tween = Some(CommandTween {
-                turtle_id: state.turtle_id,
+                turtle_id,
-                command: command_clone,
+                command,
                 start_time: get_time(),
                 duration,
-                start_params: state.params.clone(),
+                start_params: params.clone(),
                 target_params: target_state.clone(),
-                current_position: state.params.position,
+                current_position: params.position,
-                current_heading: state.params.heading,
+                current_heading: params.heading,
                 position_tweener,
                 heading_tweener,
                 pen_width_tweener,
@@ -310,7 +342,7 @@ impl TweenController {
 
     #[must_use]
     pub fn is_complete(&self) -> bool {
-        self.current_tween.is_none() && self.queue.is_complete()
+        self.current_tween.is_none() && self.cursor >= self.queue.len()
     }
 
     /// Get the current active tween if one is in progress
@@ -319,131 +351,35 @@ impl TweenController {
     }
 
     fn command_creates_drawing(command: &TurtleCommand) -> bool {
-        matches!(
+        command.produces_drawing()
-            command,
-            TurtleCommand::Move(_) | TurtleCommand::Circle { .. } | TurtleCommand::Goto(_)
-        )
     }
 
     fn calculate_duration_with_state(
         command: &TurtleCommand,
-        current: &Turtle,
+        params: &TurtleParams,
         speed: AnimationSpeed,
     ) -> f64 {
-        let mut speed = speed.value();
+        command.animation_duration(params, speed)
-
-        // For high speeds, make animation even faster by scaling speed exponentially
-        if speed > 100.0 {
-            speed *= speed / 100.0;
-        }
-
-        let base_time = match command {
-            TurtleCommand::Move(dist) => dist.abs() / speed,
-            TurtleCommand::Turn(angle) => {
-                // Rotation speed: assume 180 degrees per second at speed 100
-                angle.abs() / (speed * 1.8)
-            }
-            TurtleCommand::Circle { radius, angle, .. } => {
-                let arc_length = radius * angle.to_radians().abs();
-                arc_length / speed
-            }
-            TurtleCommand::Goto(target) => {
-                // Calculate actual distance from current position to target
-                let dx = target.x - current.params.position.x;
-                let dy = target.y - current.params.position.y;
-                let distance = (dx * dx + dy * dy).sqrt();
-                distance / speed
-            }
-            _ => 0.0, // Instant commands
-        };
-        f64::from(base_time.max(0.01)) // Minimum duration
     }
 
     fn calculate_target_state(current: &TurtleParams, command: &TurtleCommand) -> TurtleParams {
         let mut target = current.clone();
-
+        command.apply_to_params(&mut target);
-        match command {
-            TurtleCommand::Move(dist) => {
-                let dx = dist * current.heading.cos();
-                let dy = dist * current.heading.sin();
-                target.position = vec2(current.position.x + dx, current.position.y + dy);
-            }
-            TurtleCommand::Turn(angle) => {
-                target.heading = normalize_angle(current.heading + angle.to_radians());
-            }
-            TurtleCommand::Circle {
-                radius,
-                angle,
-                direction,
-                ..
-            } => {
-                // Use helper function to calculate final position
-                target.position = calculate_circle_position(
-                    current.position,
-                    current.heading,
-                    *radius,
-                    angle.to_radians(),
-                    *direction,
-                );
-                target.heading = normalize_angle(match direction {
-                    CircleDirection::Left => current.heading - angle.to_radians(),
-                    CircleDirection::Right => current.heading + angle.to_radians(),
-                });
-            }
-            TurtleCommand::Goto(coord) => {
-                // Flip Y coordinate: turtle graphics uses Y+ = up, but Macroquad uses Y+ = down
-                target.position = vec2(coord.x, -coord.y);
-            }
-            TurtleCommand::SetHeading(heading) => {
-                target.heading = normalize_angle(*heading);
-            }
-            TurtleCommand::SetColor(color) => {
-                target.color = *color;
-            }
-            TurtleCommand::SetPenWidth(width) => {
-                target.pen_width = *width;
-            }
-            TurtleCommand::SetSpeed(speed) => {
-                target.speed = *speed;
-            }
-            TurtleCommand::SetShape(shape) => {
-                target.shape = shape.clone();
-            }
-            TurtleCommand::PenUp => {
-                target.pen_down = false;
-            }
-            TurtleCommand::PenDown => {
-                target.pen_down = true;
-            }
-            TurtleCommand::ShowTurtle => {
-                target.visible = true;
-            }
-            TurtleCommand::HideTurtle => {
-                target.visible = false;
-            }
-            TurtleCommand::SetFillColor(color) => {
-                target.fill_color = *color;
-            }
-            TurtleCommand::BeginFill | TurtleCommand::EndFill | TurtleCommand::WriteText { .. } => {
-                // Fill and text commands don't change turtle state for tweening purposes
-                // They're handled directly in execution
-            }
-            TurtleCommand::Reset => {
-                // Reset returns to default state
-                target = TurtleParams::default();
-            }
-        }
-
         target
     }
 }
 
-/// Calculate position on a circular arc
+/// Calculate position on a circular arc.
+///
+/// `start_heading` is in radians (typed as `Radians` to make the unit
+/// explicit at every call site). `angle_traveled` is already a raw `f32`
+/// radians value produced by multiplying `Degrees::as_radians().value()`
+/// by a tween progress scalar.
 fn calculate_circle_position(
     start_pos: Vec2,
-    start_heading: f32,
+    start_heading: Radians,
     radius: f32,
-    angle_traveled: f32, // How much of the total angle we've traveled (in radians)
+    angle_traveled: f32,
     direction: CircleDirection,
 ) -> Vec2 {
     let geom = CircleGeometry::new(start_pos, start_heading, radius, direction);
@@ -451,7 +387,7 @@ fn calculate_circle_position(
 }
 
 /// Normalize angle to range [-PI, PI] to prevent floating-point drift
-fn normalize_angle(angle: f32) -> f32 {
+pub(crate) fn normalize_angle(angle: f32) -> f32 {
     let two_pi = std::f32::consts::PI * 2.0;
     let mut normalized = angle % two_pi;