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.

3 files changed, 200 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);
+}
diff --git a/cnn_v3/src/gbuf_deferred_effect.cc b/cnn_v3/src/gbuf_deferred_effect.cc
new file mode 100644
index 0000000..8967fe5
--- /dev/null
+++ b/cnn_v3/src/gbuf_deferred_effect.cc
@@ -0,0 +1,138 @@
+// GBufDeferredEffect — simple deferred render: albedo * shadow from packed G-buffer.
+
+#include "gbuf_deferred_effect.h"
+#include "gpu/gpu.h"
+#include "util/fatal_error.h"
+
+extern const char* gbuf_deferred_wgsl;
+
+struct GBufDeferredUniforms {
+  float resolution[2];
+};
+static_assert(sizeof(GBufDeferredUniforms) == 8, "GBufDeferredUniforms must be 8 bytes");
+
+static WGPUBindGroupLayoutEntry bgl_uint_tex(uint32_t binding) {
+  WGPUBindGroupLayoutEntry e = {};
+  e.binding               = binding;
+  e.visibility            = WGPUShaderStage_Fragment;
+  e.texture.sampleType    = WGPUTextureSampleType_Uint;
+  e.texture.viewDimension = WGPUTextureViewDimension_2D;
+  return e;
+}
+
+static WGPUBindGroupLayoutEntry bgl_uniform(uint32_t binding, uint64_t min_size) {
+  WGPUBindGroupLayoutEntry e = {};
+  e.binding               = binding;
+  e.visibility            = WGPUShaderStage_Fragment;
+  e.buffer.type           = WGPUBufferBindingType_Uniform;
+  e.buffer.minBindingSize = min_size;
+  return e;
+}
+
+GBufDeferredEffect::GBufDeferredEffect(const GpuContext& ctx,
+                                       const std::vector<std::string>& inputs,
+                                       const std::vector<std::string>& outputs,
+                                       float start_time, float end_time)
+    : Effect(ctx, inputs, outputs, start_time, end_time) {
+  HEADLESS_RETURN_IF_NULL(ctx_.device);
+
+  WGPUBindGroupLayoutEntry entries[3] = {
+      bgl_uint_tex(0),
+      bgl_uint_tex(1),
+      bgl_uniform(2, sizeof(GBufDeferredUniforms)),
+  };
+  WGPUBindGroupLayoutDescriptor bgl_desc = {};
+  bgl_desc.entryCount = 3;
+  bgl_desc.entries    = entries;
+  WGPUBindGroupLayout bgl = wgpuDeviceCreateBindGroupLayout(ctx_.device, &bgl_desc);
+
+  WGPUPipelineLayoutDescriptor pl_desc = {};
+  pl_desc.bindGroupLayoutCount = 1;
+  pl_desc.bindGroupLayouts     = &bgl;
+  WGPUPipelineLayout pl = wgpuDeviceCreatePipelineLayout(ctx_.device, &pl_desc);
+
+  WGPUShaderSourceWGSL wgsl_src = {};
+  wgsl_src.chain.sType = WGPUSType_ShaderSourceWGSL;
+  wgsl_src.code        = str_view(gbuf_deferred_wgsl);
+  WGPUShaderModuleDescriptor shader_desc = {};
+  shader_desc.nextInChain = &wgsl_src.chain;
+  WGPUShaderModule shader = wgpuDeviceCreateShaderModule(ctx_.device, &shader_desc);
+
+  WGPUColorTargetState target = {};
+  target.format    = WGPUTextureFormat_RGBA8Unorm;
+  target.writeMask = WGPUColorWriteMask_All;
+
+  WGPUFragmentState frag = {};
+  frag.module      = shader;
+  frag.entryPoint  = str_view("fs_main");
+  frag.targetCount = 1;
+  frag.targets     = &target;
+
+  WGPURenderPipelineDescriptor pipe_desc = {};
+  pipe_desc.layout               = pl;
+  pipe_desc.vertex.module        = shader;
+  pipe_desc.vertex.entryPoint    = str_view("vs_main");
+  pipe_desc.fragment             = &frag;
+  pipe_desc.primitive.topology   = WGPUPrimitiveTopology_TriangleList;
+  pipe_desc.multisample.count    = 1;
+  pipe_desc.multisample.mask     = UINT32_MAX;
+
+  pipeline_.set(wgpuDeviceCreateRenderPipeline(ctx_.device, &pipe_desc));
+
+  wgpuShaderModuleRelease(shader);
+  wgpuPipelineLayoutRelease(pl);
+  wgpuBindGroupLayoutRelease(bgl);
+}
+
+void GBufDeferredEffect::render(WGPUCommandEncoder encoder,
+                                const UniformsSequenceParams& params,
+                                NodeRegistry& nodes) {
+  WGPUTextureView feat0_view  = nodes.get_view(input_nodes_[0]);
+  WGPUTextureView feat1_view  = nodes.get_view(input_nodes_[1]);
+  WGPUTextureView output_view = nodes.get_view(output_nodes_[0]);
+
+  // Upload resolution uniform into the base class uniforms buffer (first 8 bytes).
+  GBufDeferredUniforms u;
+  u.resolution[0] = params.resolution.x;
+  u.resolution[1] = params.resolution.y;
+  wgpuQueueWriteBuffer(ctx_.queue, uniforms_buffer_.get().buffer, 0,
+                       &u, sizeof(u));
+
+  WGPUBindGroupLayout bgl =
+      wgpuRenderPipelineGetBindGroupLayout(pipeline_.get(), 0);
+
+  WGPUBindGroupEntry bg_entries[3] = {};
+  bg_entries[0].binding     = 0;
+  bg_entries[0].textureView = feat0_view;
+  bg_entries[1].binding     = 1;
+  bg_entries[1].textureView = feat1_view;
+  bg_entries[2].binding     = 2;
+  bg_entries[2].buffer      = uniforms_buffer_.get().buffer;
+  bg_entries[2].size        = sizeof(GBufDeferredUniforms);
+
+  WGPUBindGroupDescriptor bg_desc = {};
+  bg_desc.layout     = bgl;
+  bg_desc.entryCount = 3;
+  bg_desc.entries    = bg_entries;
+  bind_group_.replace(wgpuDeviceCreateBindGroup(ctx_.device, &bg_desc));
+  wgpuBindGroupLayoutRelease(bgl);
+
+  WGPURenderPassColorAttachment color_att = {};
+  color_att.view       = output_view;
+  color_att.loadOp     = WGPULoadOp_Clear;
+  color_att.storeOp    = WGPUStoreOp_Store;
+  color_att.clearValue = {0.0f, 0.0f, 0.0f, 1.0f};
+  color_att.depthSlice = WGPU_DEPTH_SLICE_UNDEFINED;
+
+  WGPURenderPassDescriptor pass_desc = {};
+  pass_desc.colorAttachmentCount = 1;
+  pass_desc.colorAttachments     = &color_att;
+
+  WGPURenderPassEncoder pass =
+      wgpuCommandEncoderBeginRenderPass(encoder, &pass_desc);
+  wgpuRenderPassEncoderSetPipeline(pass, pipeline_.get());
+  wgpuRenderPassEncoderSetBindGroup(pass, 0, bind_group_.get(), 0, nullptr);
+  wgpuRenderPassEncoderDraw(pass, 3, 1, 0, 0);
+  wgpuRenderPassEncoderEnd(pass);
+  wgpuRenderPassEncoderRelease(pass);
+}
diff --git a/cnn_v3/src/gbuf_deferred_effect.h b/cnn_v3/src/gbuf_deferred_effect.h
new file mode 100644
index 0000000..4daf13d
--- /dev/null
+++ b/cnn_v3/src/gbuf_deferred_effect.h
@@ -0,0 +1,23 @@
+// GBufDeferredEffect — simple deferred render from packed G-buffer.
+// Inputs: feat_tex0, feat_tex1 (rgba32uint). Output: albedo * shadow (rgba8unorm).
+
+#pragma once
+#include "gpu/effect.h"
+#include "gpu/uniform_helper.h"
+#include "gpu/wgpu_resource.h"
+
+class GBufDeferredEffect : public Effect {
+ public:
+  GBufDeferredEffect(const GpuContext& ctx,
+                     const std::vector<std::string>& inputs,
+                     const std::vector<std::string>& outputs,
+                     float start_time, float end_time);
+
+  void render(WGPUCommandEncoder encoder,
+              const UniformsSequenceParams& params,
+              NodeRegistry& nodes) override;
+
+ private:
+  RenderPipeline pipeline_;
+  BindGroup bind_group_;
+};