remove the bevy based turtle and rename turtle-lib-macroquad to turtle-lib

turtle-lib/examples/dragon.rs

@@ -0,0 +1,93 @@
+//! Draw a dragon curve, more specifically a Heighway dragon.
+//!
+//! (https://en.wikipedia.org/wiki/Dragon_curve)
+//!
+//! As can be seen in the above Wikipedia article, the Heighway dragon can be
+//! constructed by repeatedly folding a strip of paper and looking at the
+//! directions of the folds/turns.
+//!
+//! Starting with a strip going left to right (l2r):
+//!
+//! start|--->---l2r--->---|end
+//!
+//! you might fold it like this:
+//!
+//! end|---<---r2l---<---\
+//! start|->---l2r--->---/
+//!
+//! Getting a l2r strip, followed by a left turn, followed by a r2l strip.
+//!
+//! Folding a right to left strip:
+//!
+//! end|---<---r2l---<---|start
+//!
+//! In the same way:
+//!
+//! start|-->---l2r--->---\
+//! end|----<---r2l---<---/
+//!
+//! Would give you a l2r, followed by a right turn, followed by a r2l strip.
+//!
+//! As you can see, the only difference between the two is the direction of
+//! the turn in the middle.
+//!
+//! This folding of paper is simulated by recursively calling the dragon(..)
+//! function, passing the direction of the turn for this fold as an angle
+//! (+90 for a right turn, -90 for a left turn).
+
+use turtle_lib::*;
+
+#[turtle_main("Dragon Curve")]
+fn draw_dragon(turtle: &mut TurtlePlan) {
+    // Fast drawing
+    turtle.set_speed(1200);
+
+    // Start position
+    turtle.pen_up();
+    turtle.backward(160.0);
+    turtle.right(90.0);
+    turtle.forward(110.0);
+    turtle.pen_down();
+    turtle.set_pen_width(6.);
+
+    // Draw the dragon curve with 13 folds
+    dragon(turtle, -90.0, 13, 0.0, 255.0);
+
+    // Hide turtle when done
+    turtle.hide();
+}
+
+/// Draw the dragon curve by simulating folding a strip of paper
+///
+/// Arguments:
+/// `fold_direction`: The direction of the fold, +90 for a right, -90 for a
+/// left turn.
+/// `num_folds`: The number of times to fold the 'strip of paper'.
+/// `color_start`/`color_end`: The color at the start/end of this subsection
+/// of the curve as a number 0-255.
+fn dragon(
+    turtle: &mut TurtlePlan,
+    fold_direction: f32,
+    num_folds: usize,
+    color_start: f32,
+    color_end: f32,
+) {
+    let color_mid = (color_start + color_end) * 0.5;
+
+    if num_folds == 0 {
+        // Mapping a color number 0-255 to an RGB gradient
+        let red = ((color_mid - 128.0).abs() * 2.0).floor();
+        let green = color_mid;
+        let blue = 160.0;
+
+        turtle.set_pen_color(Color::new(red / 255.0, green / 255.0, blue / 255.0, 1.0));
+        turtle.forward(10.0);
+        return;
+    }
+
+    // Draw a left to right strip (which has a left turn in the middle)
+    dragon(turtle, -90.0, num_folds - 1, color_start, color_mid);
+    turtle.right(fold_direction);
+    // Draw a right to left strip (which has a right turn in the middle)
+    dragon(turtle, 90.0, num_folds - 1, color_mid, color_end);
+}