Add a coefficients trait for converting the affine coefficient notation flam3 uses to how glam represents it

enkou-shaders/src/lib.rs

@@ -2,11 +2,73 @@
 
 use bytemuck::{Pod, Zeroable};
 use core::f32::consts::PI;
-use glam::{Vec3, Vec4, vec2, vec3};
+use glam::{Affine2, Vec3, Vec4, vec2, vec3};
 #[cfg(target_arch = "spirv")]
 use spirv_std::num_traits::Float;
 use spirv_std::spirv;
 
+/// Utility trait for [`Affine2`] to convert between `flam3` notation and [`glam`].
+pub trait Coefficients2 {
+    /// Convert affine transformation coefficients to the [`Affine2`] representation.
+    /// Parameters use the following form:
+    ///
+    /// ```text
+    /// (a * x + b * y + c, d * x + e * y + f)
+    /// ```
+    ///
+    /// ```
+    /// # use glam::{Affine2, vec2};
+    /// # use crate::enkou_shaders::Coefficients2;
+    /// let coefs = Affine2::from_coefficients(1.0, 2.0, 3.0, 4.0, 5.0, 6.0);
+    /// let (x, y) = (7.0, 8.0);
+    /// assert_eq!(
+    ///     coefs.transform_point2(vec2(x, y)),
+    ///     vec2(
+    ///         coefs.a() * x + coefs.b() * y + coefs.c(),
+    ///         coefs.d() * x + coefs.e() * y + coefs.f()
+    ///     )
+    /// );
+    /// ```
+    fn from_coefficients(a: f32, b: f32, c: f32, d: f32, e: f32, f: f32) -> Affine2;
+
+    fn a(&self) -> f32;
+    fn b(&self) -> f32;
+    fn c(&self) -> f32;
+    fn d(&self) -> f32;
+    fn e(&self) -> f32;
+    fn f(&self) -> f32;
+}
+
+impl Coefficients2 for Affine2 {
+    fn from_coefficients(a: f32, b: f32, c: f32, d: f32, e: f32, f: f32) -> Affine2 {
+        Affine2::from_cols_array(&[a, d, b, e, c, f])
+    }
+
+    fn a(&self) -> f32 {
+        self.matrix2.x_axis.x
+    }
+
+    fn b(&self) -> f32 {
+        self.matrix2.y_axis.x
+    }
+
+    fn c(&self) -> f32 {
+        self.translation.x
+    }
+
+    fn d(&self) -> f32 {
+        self.matrix2.x_axis.y
+    }
+
+    fn e(&self) -> f32 {
+        self.matrix2.y_axis.y
+    }
+
+    fn f(&self) -> f32 {
+        self.translation.y
+    }
+}
+
 #[derive(Copy, Clone, Pod, Zeroable)]
 #[repr(C)]
 pub struct ShaderConstants {