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, 69 insertions, 0 deletions

diff --git a/common/shaders/render/fullscreen_vs.wgsl b/common/shaders/render/fullscreen_vs.wgsl
new file mode 100644
index 0000000..a68604b
--- /dev/null
+++ b/common/shaders/render/fullscreen_vs.wgsl
@@ -0,0 +1,10 @@
+// Common vertex shader for fullscreen post-processing effects.
+// Draws a single triangle that covers the entire screen.
+@vertex fn vs_main(@builtin(vertex_index) i: u32) -> @builtin(position) vec4<f32> {
+    var pos = array<vec2<f32>, 3>(
+        vec2<f32>(-1, -1),
+        vec2<f32>(3, -1),
+        vec2<f32>(-1, 3)
+    );
+    return vec4<f32>(pos[i], 0.0, 1.0);
+}
diff --git a/common/shaders/render/raymarching.wgsl b/common/shaders/render/raymarching.wgsl
new file mode 100644
index 0000000..5a86840
--- /dev/null
+++ b/common/shaders/render/raymarching.wgsl
@@ -0,0 +1,59 @@
+// Common functions for Signed Distance Field (SDF) raymarching.
+// These functions require the user to define a `df(vec3<f32>) -> f32` function
+// which represents the scene's distance field.
+
+const TOLERANCE: f32 = 0.0005;
+const MAX_RAY_LENGTH: f32 = 20.0;
+const MAX_RAY_MARCHES: i32 = 80;
+const NORM_OFF: f32 = 0.005;
+
+// Computes the surface normal of the distance field at a point `pos`.
+fn normal(pos: vec3<f32>) -> vec3<f32> {
+  let eps = vec2<f32>(NORM_OFF, 0.0);
+  var nor: vec3<f32>;
+  nor.x = df(pos + eps.xyy) - df(pos - eps.xyy);
+  nor.y = df(pos + eps.yxy) - df(pos - eps.yxy);
+  nor.z = df(pos + eps.yyx) - df(pos - eps.yyx);
+  return normalize(nor);
+}
+
+// Performs the raymarching operation.
+// Returns the distance along the ray to the surface, or MAX_RAY_LENGTH if no surface is hit.
+fn rayMarch(ro: vec3<f32>, rd: vec3<f32>, initt: f32) -> f32 {
+  var t = initt;
+  for (var i = 0; i < MAX_RAY_MARCHES; i++) {
+    if (t > MAX_RAY_LENGTH) {
+      t = MAX_RAY_LENGTH;
+      break;
+    }
+    let d = df(ro + rd * t);
+    if (d < TOLERANCE) {
+      break;
+    }
+    t += d;
+  }
+  return t;
+}
+
+// Computes a soft shadow for a given point.
+fn shadow(lp: vec3<f32>, ld: vec3<f32>, mint: f32, maxt: f32) -> f32 {
+  let ds = 1.0 - 0.4;
+  var t = mint;
+  var nd = 1e6;
+  let soff = 0.05;
+  let smul = 1.5;
+  let MAX_SHD_MARCHES = 20;
+
+  for (var i = 0; i < MAX_SHD_MARCHES; i++) {
+    let p = lp + ld * t;
+    let d = df(p);
+    if (d < TOLERANCE || t >= maxt) {
+      let sd = 1.0 - exp(-smul * max(t / maxt - soff, 0.0));
+      return select(mix(sd, 1.0, smoothstep(0.0, 0.025, nd)), sd, t >= maxt);
+    }
+    nd = min(nd, d);
+    t += ds * d;
+  }
+  let sd = 1.0 - exp(-smul * max(t / maxt - soff, 0.0));
+  return sd;
+}