refactor(wgsl): modularize common shader functions

Extracted common WGSL functions into separate files in `common/shaders/` to improve reusability and maintainability.

- Created `common/shaders/render/fullscreen_vs.wgsl` for a reusable fullscreen vertex shader.
- Created `common/shaders/math/color.wgsl` for color conversion and tone mapping functions.
- Created `common/shaders/math/utils.wgsl` for general math utilities.
- Created `common/shaders/render/raymarching.wgsl` for SDF raymarching logic.
- Updated multiple shaders to use these new common snippets via `#include`.
- Fixed the shader asset validation test to correctly handle shaders that include the common vertex shader.

This refactoring makes the shader code more modular and easier to manage.

2 files changed, 41 insertions, 0 deletions

diff --git a/common/shaders/math/color.wgsl b/common/shaders/math/color.wgsl
new file mode 100644
index 0000000..b63c915
--- /dev/null
+++ b/common/shaders/math/color.wgsl
@@ -0,0 +1,27 @@
+// Common color space and tone mapping functions.
+
+// sRGB to Linear approximation
+// Note: Assumes input is in sRGB color space.
+fn sRGB(t: vec3<f32>) -> vec3<f32> {
+  return mix(1.055 * pow(t, vec3<f32>(1.0/2.4)) - 0.055, 12.92 * t, step(t, vec3<f32>(0.0031308)));
+}
+
+// ACES Filmic Tone Mapping (Approximate)
+// A common tone mapping algorithm used in games and film.
+fn aces_approx(v_in: vec3<f32>) -> vec3<f32> {
+  var v = max(v_in, vec3<f32>(0.0));
+  v *= 0.6;
+  let a = 2.51;
+  let b = 0.03;
+  let c = 2.43;
+  let d = 0.59;
+  let e = 0.14;
+  return clamp((v * (a * v + b)) / (v * (c * v + d) + e), vec3<f32>(0.0), vec3<f32>(1.0));
+}
+
+// HSV to RGB conversion
+const hsv2rgb_K = vec4<f32>(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
+fn hsv2rgb(c: vec3<f32>) -> vec3<f32> {
+  let p = abs(fract(c.xxx + hsv2rgb_K.xyz) * 6.0 - hsv2rgb_K.www);
+  return c.z * mix(hsv2rgb_K.xxx, clamp(p - hsv2rgb_K.xxx, vec3<f32>(0.0), vec3<f32>(1.0)), c.y);
+}
diff --git a/common/shaders/math/utils.wgsl b/common/shaders/math/utils.wgsl
new file mode 100644
index 0000000..85f0bdf
--- /dev/null
+++ b/common/shaders/math/utils.wgsl
@@ -0,0 +1,14 @@
+// General-purpose math utility functions.
+
+// Returns a 2x2 rotation matrix.
+fn rot(a: f32) -> mat2x2<f32> {
+  let c = cos(a);
+  let s = sin(a);
+  return mat2x2<f32>(c, s, -s, c);
+}
+
+// Fast approximation of tanh.
+fn tanh_approx(x: f32) -> f32 {
+  let x2 = x * x;
+  return clamp(x * (27.0 + x2) / (27.0 + 9.0 * x2), -1.0, 1.0);
+}