Implement post-transform coefficients

enkou-shaders/examples/gasket.rs

@@ -17,21 +17,21 @@ const IMAGE_DIMENSION: UVec2 = uvec2(600, 600);
 
 pub fn main() -> Result<()> {
     let transforms = [
-        // F_0: (x / 2, y / 2)
-        Transform::new(
-            Affine2::from_coefficients(0.5, 0.0, 0.0, 0.0, 0.5, 0.0),
-            uvec2(0, 1),
-        ),
-        // F_1: ((x + 1) / 2, y / 2)
-        Transform::new(
-            Affine2::from_coefficients(0.5, 0.0, 0.5, 0.0, 0.5, 0.0),
-            uvec2(0, 1),
-        ),
-        // F_2: (x / 2, (y + 1) / 2)
-        Transform::new(
-            Affine2::from_coefficients(0.5, 0.0, 0.0, 0.0, 0.5, 0.5),
-            uvec2(0, 1),
-        ),
+        {
+            // F_0: (x / 2, y / 2)
+            let coefficients = Affine2::from_coefficients(0.5, 0.0, 0.0, 0.0, 0.5, 0.0);
+            Transform::new(coefficients, Affine2::IDENTITY, uvec2(0, 1))
+        },
+        {
+            // F_1: ((x + 1) / 2, y / 2)
+            let coefficients = Affine2::from_coefficients(0.5, 0.0, 0.5, 0.0, 0.5, 0.0);
+            Transform::new(coefficients, Affine2::IDENTITY, uvec2(0, 1))
+        },
+        {
+            // F_2: (x / 2, (y + 1) / 2)
+            let coefficients = Affine2::from_coefficients(0.5, 0.0, 0.0, 0.0, 0.5, 0.5);
+            Transform::new(coefficients, Affine2::IDENTITY, uvec2(0, 1))
+        },
     ];
 
     let weights = [1.0 / 3.0, 1.0 / 3.0, 1.0 / 3.0];

enkou-shaders/src/transform.rs

@@ -13,14 +13,16 @@ use rand::Rng;
 #[repr(C)]
 pub struct Transform {
     coefficients: Affine2,
+    coefficients_post: Affine2,
     variation_range: UVec2,
 }
 
 impl Transform {
     /// Create a new transform from an affine transformation matrix
-    pub fn new(coefficients: Affine2, variation_range: UVec2) -> Self {
+    pub fn new(coefficients: Affine2, coefficients_post: Affine2, variation_range: UVec2) -> Self {
         Transform {
             coefficients,
+            coefficients_post,
             variation_range,
         }
     }
@@ -43,6 +45,53 @@ impl Transform {
             point_output += variation.transform_point(point, rng, &self.coefficients)
         }
 
-        point_output
+        self.coefficients_post.transform_point2(point)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use crate::rng::xoshiro256starstar_from_seed;
+    use crate::transform::Transform;
+    use crate::variation::{Variation, VariationKind};
+    use glam::{Affine2, uvec2, vec2};
+
+    #[test]
+    fn transform_scaling() {
+        let scale_coefficients = vec2(2.0, 0.5);
+        let transform = Transform::new(
+            Affine2::from_scale(scale_coefficients),
+            Affine2::IDENTITY,
+            uvec2(0, 1),
+        );
+
+        let mut rng = xoshiro256starstar_from_seed([0; 32]);
+        let variations = [Variation::IDENTITY];
+        let point = vec2(1.0, 1.0);
+
+        assert_eq!(
+            transform.transform_point(&mut rng, &variations, point),
+            scale_coefficients
+        );
+    }
+
+    #[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_post = Transform::new(
+            Affine2::IDENTITY,
+            Affine2::from_scale(scale_coefficients),
+            uvec2(0, 1),
+        );
+
+        let mut rng = xoshiro256starstar_from_seed([0; 32]);
+        let variations = [Variation::new(VariationKind::Pdj, 1.0, [0.0f32; 4].into())];
+        let point = vec2(1.0, 1.0);
+
+        let point_pdj = transform_pdj.transform_point(&mut rng, &variations, point);
+        let point_pdj_post = transform_pdj_post.transform_point(&mut rng, &variations, point);
+
+        assert_eq!(point_pdj * scale_coefficients, point_pdj_post);
     }
 }

enkou-shaders/src/variation.rs

@@ -20,6 +20,12 @@ use rand::{Rng, RngExt};
 #[repr(C)]
 pub struct VariationParams([f32; 4]);
 
+impl From<[f32; 4]> for VariationParams {
+    fn from(v: [f32; 4]) -> Self {
+        VariationParams(v)
+    }
+}
+
 /// Enum for all supported variation types
 ///
 /// ID numbers are chosen to match the variation identifier also used by `flam3`