fix(scene2): rewrite broken WGSL shader to fix test_demo_effects crash

scene2.wgsl was invalid WGSL (mixed GLSL syntax, wrong function signatures,
undeclared variables, no return statement). Rewrote as valid WGSL preserving
the original volumetric cloud raymarching logic. 11/11 effects now pass.

handoff(Claude): scene2.wgsl fixed, all tests green.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 23 insertions, 29 deletions

diff --git a/workspaces/main/shaders/scene2.wgsl b/workspaces/main/shaders/scene2.wgsl
index 486f41e..7df91c3 100644
--- a/workspaces/main/shaders/scene2.wgsl
+++ b/workspaces/main/shaders/scene2.wgsl
@@ -1,4 +1,4 @@
-// Scene2 effect shader - ShaderToy conversion
+// Scene2 effect shader - ShaderToy conversion (volumetric clouds)
 // Generated by convert_shadertoy.py
 // NOTE: Manual review recommended - conversion is basic
 
@@ -7,37 +7,31 @@
 
 @group(0) @binding(2) var<uniform> uniforms: UniformsSequenceParams;
 
-
-fn N(vec3f a, vec3f p) { return abs(dot(sin(uniforms.time+.1*p.z+.3*p / a), vec3f(a+a))); }
-const NUM_LAYERS: f32 = 12.;
-
-
+fn N(a: vec3f, p: vec3f) -> f32 {
+    return abs(dot(sin(uniforms.time + 0.1 * p.z + 0.3 * p / a), a + a));
+}
 
 @fragment fn fs_main(in: VertexOutput) -> @location(0) vec4f {
-  // Flip Y to match ShaderToy convention (origin at bottom-left)
-  let flipped = vec2f(in.position.x, uniforms.resolution.y - in.position.y);
-  let q = flipped / uniforms.resolution;
-  var coord = -1.0 + 2.0 * q;
-  coord.x *= uniforms.resolution.x / uniforms.resolution.y;
-
-  f32 i,s;
-      vec3f  p = vec3f[0),r = uniforms.resolution;    
+    let r = uniforms.resolution;
+    let frag_coord = vec2f(in.position.x, r.y - in.position.y);
+    let u = (frag_coord + frag_coord - r) / r.y;
 
-      vec2f uv = (u-.5*uniforms.resolution.xy)/uniforms.resolution.y;
+    var p = vec3f(0.0);
+    var col = vec4f(0.0);
+    var s: f32 = 0.0;
 
-      f32 t = uniforms.time*.0; 
-      vec3f col = vec3f(0);  
+    for (var i: f32 = 0.0; i < 100.0; i += 1.0) {
+        p += vec3f(u * s, s);
+        s = 6.0 + p.y;
+        s -= N(vec3f(0.08), p);
+        s -= N(vec3f(0.2), p);
+        s -= N(vec3f(0.6), p);
+        s = 0.1 + abs(s) * 0.2;
+        col += vec4f(4.0, 2.0, 1.0, 0.0) / s;
+    }
 
-      u = (u+u-r.xy)/r.y;
-      for(o*=i; i++<1e2; ) {
-          p += vec3f(u * s, s);
-          s = 6.+(p.y);
-          s -= N(.08);
-          s -= N(.2);
-          s -= N(.6);
-          s = .1 + abs(s)*.2;
-          o +=  vec4f(4,2,1,0)/s;
-      }
-      o *= smoothstep(0.8, 0.75, abs(u.y));
-      o = tanh(o / 2e3 / length(u));
+    col *= smoothstep(0.8, 0.75, abs(u.y));
+    let len_u = max(length(u), 0.0001);
+    col = tanh(col / 2000.0 / len_u);
+    return vec4f(col.rgb, 1.0);
 }