feat(gpu): Phase 2 - Add gen_perlin and gen_grid GPU compute shaders

Complete Phase 2 implementation:
- gen_perlin.wgsl: FBM with configurable octaves, amplitude decay
- gen_grid.wgsl: Grid pattern with configurable spacing/thickness
- TextureManager extensions: create_gpu_perlin_texture(), create_gpu_grid_texture()
- Asset packer now validates gen_noise, gen_perlin, gen_grid for PROC_GPU()
- 3 compute pipelines (lazy-init on first use)

Shader parameters:
- gen_perlin: seed, frequency, amplitude, amplitude_decay, octaves (32 bytes)
- gen_grid: width, height, grid_size, thickness (16 bytes)

test_3d_render migration:
- Replaced CPU sky texture (gen_perlin) with GPU version
- Replaced CPU noise texture (gen_noise) with GPU version
- Added new GPU grid texture (256x256, 32px grid, 2px lines)

Size impact:
- gen_perlin.wgsl: ~200 bytes (compressed)
- gen_grid.wgsl: ~100 bytes (compressed)
- Total Phase 2 code: ~300 bytes
- Cumulative (Phase 1+2): ~600 bytes

Testing:
- All 34 tests passing (100%)
- test_gpu_procedural validates all generators
- test_3d_render uses 3 GPU textures (noise, perlin, grid)

Next: Phase 3 - Variable dimensions, async generation, pipeline caching

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/assets/final/shaders/compute/gen_grid.wgsl b/assets/final/shaders/compute/gen_grid.wgsl
new file mode 100644
index 0000000..cc5e189
--- /dev/null
+++ b/assets/final/shaders/compute/gen_grid.wgsl
@@ -0,0 +1,24 @@
+// GPU procedural grid pattern generator.
+// Simple grid lines with configurable spacing and thickness.
+
+struct GridParams {
+  width: u32,
+  height: u32,
+  grid_size: u32,
+  thickness: u32,
+}
+
+@group(0) @binding(0) var output_tex: texture_storage_2d<rgba8unorm, write>;
+@group(0) @binding(1) var<uniform> params: GridParams;
+
+@compute @workgroup_size(8, 8, 1)
+fn main(@builtin(global_invocation_id) id: vec3<u32>) {
+  if (id.x >= params.width || id.y >= params.height) { return; }
+
+  let on_line = (id.x % params.grid_size) < params.thickness ||
+                (id.y % params.grid_size) < params.thickness;
+
+  let val = select(0.0, 1.0, on_line);
+
+  textureStore(output_tex, id.xy, vec4<f32>(val, val, val, 1.0));
+}