94 lines
2.7 KiB
Rust
94 lines
2.7 KiB
Rust
//! Draw a dragon curve, more specifically a Heighway dragon.
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//!
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//! (https://en.wikipedia.org/wiki/Dragon_curve)
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//!
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//! As can be seen in the above Wikipedia article, the Heighway dragon can be
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//! constructed by repeatedly folding a strip of paper and looking at the
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//! directions of the folds/turns.
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//!
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//! Starting with a strip going left to right (l2r):
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//!
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//! start|--->---l2r--->---|end
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//!
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//! you might fold it like this:
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//!
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//! end|---<---r2l---<---\
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//! start|->---l2r--->---/
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//!
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//! Getting a l2r strip, followed by a left turn, followed by a r2l strip.
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//!
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//! Folding a right to left strip:
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//!
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//! end|---<---r2l---<---|start
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//!
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//! In the same way:
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//!
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//! start|-->---l2r--->---\
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//! end|----<---r2l---<---/
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//!
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//! Would give you a l2r, followed by a right turn, followed by a r2l strip.
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//!
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//! As you can see, the only difference between the two is the direction of
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//! the turn in the middle.
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//!
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//! This folding of paper is simulated by recursively calling the dragon(..)
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//! function, passing the direction of the turn for this fold as an angle
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//! (+90 for a right turn, -90 for a left turn).
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use turtle_lib::*;
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#[turtle_main("Dragon Curve")]
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fn draw_dragon(turtle: &mut TurtlePlan) {
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// Fast drawing
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turtle.set_speed(1020);
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// Start position
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turtle.pen_up();
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turtle.backward(160.0);
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turtle.right(90.0);
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turtle.forward(110.0);
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turtle.pen_down();
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turtle.set_pen_width(6.);
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// Draw the dragon curve with 13 folds
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dragon(turtle, -90.0, 13, 0.0, 255.0);
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// Hide turtle when done
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turtle.hide();
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}
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/// Draw the dragon curve by simulating folding a strip of paper
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///
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/// Arguments:
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/// `fold_direction`: The direction of the fold, +90 for a right, -90 for a
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/// left turn.
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/// `num_folds`: The number of times to fold the 'strip of paper'.
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/// `color_start`/`color_end`: The color at the start/end of this subsection
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/// of the curve as a number 0-255.
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fn dragon(
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turtle: &mut TurtlePlan,
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fold_direction: f32,
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num_folds: usize,
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color_start: f32,
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color_end: f32,
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) {
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let color_mid = (color_start + color_end) * 0.5;
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if num_folds == 0 {
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// Mapping a color number 0-255 to an RGB gradient
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let red = ((color_mid - 128.0).abs() * 2.0).floor();
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let green = color_mid;
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let blue = 160.0;
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turtle.set_pen_color(Color::new(red / 255.0, green / 255.0, blue / 255.0, 1.0));
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turtle.forward(10.0);
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return;
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}
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// Draw a left to right strip (which has a left turn in the middle)
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dragon(turtle, -90.0, num_folds - 1, color_start, color_mid);
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turtle.right(fold_direction);
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// Draw a right to left strip (which has a right turn in the middle)
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dragon(turtle, 90.0, num_folds - 1, color_mid, color_end);
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}
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