Add a color coordinate to the chaos game

Also refactors the gasket example to avoid using shader entry points; the entry point signatures are not stable, and I don't want to keep refactoring the gasket while adding more advanced color/image features.

enkou-shaders/src/transform.rs

@@ -5,7 +5,7 @@
 //! but produce more interesting images once we add variations.
 use crate::variation::Variation;
 use bytemuck::{Pod, Zeroable};
-use glam::{Affine2, UVec2, Vec2};
+use glam::{Affine2, FloatExt, UVec2, Vec2};
 use rand::Rng;
 
 /// Affine transform for use in the [`chaos_game`](crate::chaos_game).
@@ -15,15 +15,22 @@ pub struct Transform {
     coefficients: Affine2,
     coefficients_post: Affine2,
     variation_range: UVec2,
+    color: Vec2,
 }
 
 impl Transform {
     /// Create a new transform from an affine transformation matrix
-    pub fn new(coefficients: Affine2, coefficients_post: Affine2, variation_range: UVec2) -> Self {
+    pub fn new(
+        coefficients: Affine2,
+        coefficients_post: Affine2,
+        variation_range: UVec2,
+        color: Vec2,
+    ) -> Self {
         Transform {
             coefficients,
             coefficients_post,
             variation_range,
+            color,
         }
     }
 
@@ -47,6 +54,11 @@ impl Transform {
 
         self.coefficients_post.transform_point2(point)
     }
+
+    /// Apply this transform to a color
+    pub fn transform_color(&self, color: f32) -> f32 {
+        color.lerp(self.color.x, self.color.y)
+    }
 }
 
 #[cfg(test)]
@@ -54,7 +66,7 @@ mod test {
     use crate::rng::xoshiro256starstar_from_seed;
     use crate::transform::Transform;
     use crate::variation::{Variation, VariationKind};
-    use glam::{Affine2, uvec2, vec2};
+    use glam::{Affine2, uvec2, vec2, Vec2};
 
     #[test]
     fn transform_scaling() {
@@ -63,6 +75,7 @@ mod test {
             Affine2::from_scale(scale_coefficients),
             Affine2::IDENTITY,
             uvec2(0, 1),
+            Vec2::ZERO,
         );
 
         let mut rng = xoshiro256starstar_from_seed([0; 32]);
@@ -78,11 +91,12 @@ mod test {
     #[test]
     fn transform_scaling_post() {
         let scale_coefficients = vec2(2.0, 0.5);
-        let transform_pdj = Transform::new(Affine2::IDENTITY, Affine2::IDENTITY, uvec2(0, 1));
+        let transform_pdj = Transform::new(Affine2::IDENTITY, Affine2::IDENTITY, uvec2(0, 1), Vec2::ZERO);
         let transform_pdj_post = Transform::new(
             Affine2::IDENTITY,
             Affine2::from_scale(scale_coefficients),
             uvec2(0, 1),
+            Vec2::ZERO,
         );
 
         let mut rng = xoshiro256starstar_from_seed([0; 32]);
@@ -94,4 +108,23 @@ mod test {
 
         assert_eq!(point_pdj * scale_coefficients, point_pdj_post);
     }
+    
+    #[test]
+    fn transform_color() {
+        // Color 0.5, color speed 1.0, so color value will always be 0.5 after transform
+        let color = vec2(0.5, 1.0);
+        let transform = Transform::new(Affine2::IDENTITY, Affine2::IDENTITY, uvec2(0, 1), color);
+
+        assert_eq!(transform.transform_color(0.0), 0.5);
+        assert_eq!(transform.transform_color(1.0), 0.5);
+        assert_eq!(transform.transform_color(2.0), 0.5);
+        
+        // Color 1.0, color speed 0.5, so color value moves to halfway between current and 1.0
+        let color = vec2(1.0, 0.5);
+        let transform = Transform::new(Affine2::IDENTITY, Affine2::IDENTITY, uvec2(0, 1), color);
+        
+        assert_eq!(transform.transform_color(0.0), 0.5);
+        assert_eq!(transform.transform_color(1.0), 1.0);
+        assert_eq!(transform.transform_color(2.0), 1.0);
+    }
 }