feat(cnn_v3): G-buffer phase 1 + training infrastructure

G-buffer (Phase 1):
- Add NodeTypes GBUF_ALBEDO/DEPTH32/R8/RGBA32UINT to NodeRegistry
- GBufferEffect: MRT raster pass (albedo+normal_mat+depth) + pack compute
- Shaders: gbuf_raster.wgsl (MRT), gbuf_pack.wgsl (feature packing, 32B/px)
- Shadow/SDF passes stubbed (placeholder textures), CMake integration deferred

Training infrastructure (Phase 2):
- blender_export.py: headless EXR export with all G-buffer render passes
- pack_blender_sample.py: EXR → per-channel PNGs (oct-normals, 1/z depth)
- pack_photo_sample.py: photo → zero-filled G-buffer sample layout

handoff(Gemini): G-buffer phases 3-5 remain (U-Net shaders, CNNv3Effect, parity)

1 files changed, 79 insertions, 0 deletions

diff --git a/cnn_v3/src/gbuffer_effect.h b/cnn_v3/src/gbuffer_effect.h
new file mode 100644
index 0000000..42fb0ec
--- /dev/null
+++ b/cnn_v3/src/gbuffer_effect.h
@@ -0,0 +1,79 @@
+// GBufferEffect: Multi-pass G-buffer rendering for CNN v3 input
+// Outputs: gbuf_feat0, gbuf_feat1 (packed rgba32uint feature textures, 32 bytes/pixel)
+
+#pragma once
+
+#include "3d/camera.h"
+#include "3d/scene.h"
+#include "gpu/effect.h"
+#include "gpu/sequence.h"
+#include "gpu/uniform_helper.h"
+#include "gpu/wgpu_resource.h"
+#include "util/mini_math.h"
+
+// Uniform for the pack compute shader
+struct GBufResUniforms {
+  vec2 resolution;
+  float _pad0;
+  float _pad1;
+};
+static_assert(sizeof(GBufResUniforms) == 16,
+              "GBufResUniforms must be 16 bytes");
+
+class GBufferEffect : public Effect {
+ public:
+  GBufferEffect(const GpuContext& ctx, const std::vector<std::string>& inputs,
+                const std::vector<std::string>& outputs, float start_time,
+                float end_time);
+
+  void declare_nodes(NodeRegistry& registry) override;
+
+  void render(WGPUCommandEncoder encoder, const UniformsSequenceParams& params,
+              NodeRegistry& nodes) override;
+
+  void set_scene(const Scene* scene, const Camera* camera);
+
+ private:
+  // Internal G-buffer node names
+  std::string node_albedo_;
+  std::string node_normal_mat_;
+  std::string node_depth_;
+  std::string node_shadow_;
+  std::string node_transp_;
+  std::string node_feat0_;
+  std::string node_feat1_;
+
+  const Scene*  scene_  = nullptr;
+  const Camera* camera_ = nullptr;
+
+  // Pass 1: MRT rasterization pipeline
+  RenderPipeline raster_pipeline_;
+  BindGroup      raster_bind_group_;
+
+  // Pass 4: Pack compute pipeline
+  ComputePipeline  pack_pipeline_;
+  BindGroup        pack_bind_group_;
+  UniformBuffer<GBufResUniforms> pack_res_uniform_;
+
+  // Placeholder textures for shadow/transp (white/black cleared once)
+  Texture     shadow_placeholder_tex_;
+  TextureView shadow_placeholder_view_;
+  Texture     transp_placeholder_tex_;
+  TextureView transp_placeholder_view_;
+
+  // GPU-side object data buffers (global uniforms + objects storage)
+  // These mirror the layout expected by gbuf_raster.wgsl
+  GpuBuffer global_uniforms_buf_;
+  GpuBuffer objects_buf_;
+  int       objects_buf_capacity_ = 0; // number of ObjectData slots allocated
+
+  void create_raster_pipeline();
+  void create_pack_pipeline();
+
+  void update_raster_bind_group(NodeRegistry& nodes);
+  void update_pack_bind_group(NodeRegistry& nodes);
+
+  void upload_scene_data(const Scene& scene, const Camera& camera,
+                         float time);
+  void ensure_objects_buffer(int num_objects);
+};