feat(cnn_v3): GBufDeferredEffect — simple deferred render (albedo * shadow)

New effect unpacks feat_tex0/feat_tex1 and outputs albedo * shadow.
Replaces CNNv3Effect in cnn_v3_test sequence until training is complete.
37/37 tests passing.

handoff(Gemini): GBufDeferredEffect wired in timeline; CNN v3 pipeline: GBufferEffect → GBufDeferredEffect → sink.

1 files changed, 39 insertions, 0 deletions

diff --git a/cnn_v3/shaders/gbuf_deferred.wgsl b/cnn_v3/shaders/gbuf_deferred.wgsl
new file mode 100644
index 0000000..959ab60
--- /dev/null
+++ b/cnn_v3/shaders/gbuf_deferred.wgsl
@@ -0,0 +1,39 @@
+// G-buffer deferred render — albedo * shadow
+// Reads feat_tex0 (rgba32uint, f16 geometric) and feat_tex1 (rgba32uint, u8 context).
+// Unpacks albedo and shadow and outputs albedo * shadow.
+
+@group(0) @binding(0) var feat_tex0: texture_2d<u32>;
+@group(0) @binding(1) var feat_tex1: texture_2d<u32>;
+@group(0) @binding(2) var<uniform> uniforms: GBufDeferredUniforms;
+
+struct GBufDeferredUniforms {
+    resolution: vec2f,
+}
+
+@vertex
+fn vs_main(@builtin(vertex_index) vid: u32) -> @builtin(position) vec4f {
+    let x = f32((vid & 1u) << 2u) - 1.0;
+    let y = f32((vid & 2u) << 1u) - 1.0;
+    return vec4f(x, y, 0.0, 1.0);
+}
+
+@fragment
+fn fs_main(@builtin(position) pos: vec4f) -> @location(0) vec4f {
+    let coord = vec2i(pos.xy);
+
+    // feat_tex0 layout:
+    //   [0] pack2x16float(albedo.r, albedo.g)
+    //   [1] pack2x16float(albedo.b, normal.x)
+    let t0 = textureLoad(feat_tex0, coord, 0);
+    let rg  = unpack2x16float(t0.x);
+    let bx  = unpack2x16float(t0.y);
+    let albedo = vec3f(rg.x, rg.y, bx.x);
+
+    // feat_tex1 layout:
+    //   [2] pack4x8unorm(mip2.g, mip2.b, shadow, transp)
+    let t1     = textureLoad(feat_tex1, coord, 0);
+    let ctx2   = unpack4x8unorm(t1.z);
+    let shadow = ctx2.z;  // shadow is the third byte
+
+    return vec4f(albedo * shadow, 1.0);
+}