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, 105 insertions, 0 deletions

diff --git a/cnn_v3/shaders/gbuf_raster.wgsl b/cnn_v3/shaders/gbuf_raster.wgsl
new file mode 100644
index 0000000..c762db2
--- /dev/null
+++ b/cnn_v3/shaders/gbuf_raster.wgsl
@@ -0,0 +1,105 @@
+// G-buffer rasterization shader for CNN v3
+// Pass 1: Proxy geometry → MRT (albedo rgba16float, normal_mat rgba16float, depth32)
+// Uses GlobalUniforms, ObjectData, ObjectsBuffer from common_uniforms.
+
+#include "common_uniforms"
+
+@group(0) @binding(0) var<uniform> globals: GlobalUniforms;
+@group(0) @binding(1) var<storage, read> object_data: ObjectsBuffer;
+
+struct VertexOutput {
+    @builtin(position)              position:       vec4f,
+    @location(0)                    world_pos:      vec3f,
+    @location(1)                    world_normal:   vec3f,
+    @location(2)                    color:          vec4f,
+    @location(3) @interpolate(flat) instance_index: u32,
+}
+
+// Octahedral encoding: maps unit normal to [-1,1]^2
+fn oct_encode(n: vec3f) -> vec2f {
+    let inv_l1 = 1.0 / (abs(n.x) + abs(n.y) + abs(n.z));
+    var p = n.xy * inv_l1;
+    // Fold lower hemisphere
+    if (n.z < 0.0) {
+        let s = vec2f(
+            select(-1.0, 1.0, p.x >= 0.0),
+            select(-1.0, 1.0, p.y >= 0.0)
+        );
+        p = (1.0 - abs(p.yx)) * s;
+    }
+    return p; // in [-1, 1]
+}
+
+@vertex
+fn vs_main(
+    @builtin(vertex_index)   vertex_index:   u32,
+    @builtin(instance_index) instance_index: u32
+) -> VertexOutput {
+    // Proxy box vertices (same as renderer_3d.wgsl)
+    var pos = array<vec3f, 36>(
+        vec3f(-1.0, -1.0,  1.0), vec3f( 1.0, -1.0,  1.0), vec3f( 1.0,  1.0,  1.0),
+        vec3f(-1.0, -1.0,  1.0), vec3f( 1.0,  1.0,  1.0), vec3f(-1.0,  1.0,  1.0),
+        vec3f(-1.0, -1.0, -1.0), vec3f(-1.0,  1.0, -1.0), vec3f( 1.0,  1.0, -1.0),
+        vec3f(-1.0, -1.0, -1.0), vec3f( 1.0,  1.0, -1.0), vec3f( 1.0, -1.0, -1.0),
+        vec3f(-1.0,  1.0, -1.0), vec3f(-1.0,  1.0,  1.0), vec3f( 1.0,  1.0,  1.0),
+        vec3f(-1.0,  1.0, -1.0), vec3f( 1.0,  1.0,  1.0), vec3f( 1.0,  1.0, -1.0),
+        vec3f(-1.0, -1.0, -1.0), vec3f( 1.0, -1.0, -1.0), vec3f( 1.0, -1.0,  1.0),
+        vec3f(-1.0, -1.0, -1.0), vec3f( 1.0, -1.0,  1.0), vec3f(-1.0, -1.0,  1.0),
+        vec3f( 1.0, -1.0, -1.0), vec3f( 1.0,  1.0, -1.0), vec3f( 1.0,  1.0,  1.0),
+        vec3f( 1.0, -1.0, -1.0), vec3f( 1.0,  1.0,  1.0), vec3f( 1.0, -1.0,  1.0),
+        vec3f(-1.0, -1.0, -1.0), vec3f(-1.0, -1.0,  1.0), vec3f(-1.0,  1.0,  1.0),
+        vec3f(-1.0, -1.0, -1.0), vec3f(-1.0,  1.0,  1.0), vec3f(-1.0,  1.0, -1.0)
+    );
+
+    // Proxy face normals (one per 2 triangles = 6 faces × 6 verts = 36)
+    var nrm = array<vec3f, 36>(
+        vec3f(0,0,1), vec3f(0,0,1), vec3f(0,0,1),
+        vec3f(0,0,1), vec3f(0,0,1), vec3f(0,0,1),
+        vec3f(0,0,-1), vec3f(0,0,-1), vec3f(0,0,-1),
+        vec3f(0,0,-1), vec3f(0,0,-1), vec3f(0,0,-1),
+        vec3f(0,1,0), vec3f(0,1,0), vec3f(0,1,0),
+        vec3f(0,1,0), vec3f(0,1,0), vec3f(0,1,0),
+        vec3f(0,-1,0), vec3f(0,-1,0), vec3f(0,-1,0),
+        vec3f(0,-1,0), vec3f(0,-1,0), vec3f(0,-1,0),
+        vec3f(1,0,0), vec3f(1,0,0), vec3f(1,0,0),
+        vec3f(1,0,0), vec3f(1,0,0), vec3f(1,0,0),
+        vec3f(-1,0,0), vec3f(-1,0,0), vec3f(-1,0,0),
+        vec3f(-1,0,0), vec3f(-1,0,0), vec3f(-1,0,0)
+    );
+
+    let obj = object_data.objects[instance_index];
+    let p = pos[vertex_index];
+    let n = nrm[vertex_index];
+
+    let world_pos    = obj.model * vec4f(p, 1.0);
+    let clip_pos     = globals.view_proj * world_pos;
+    // Transform normal by inverse-transpose (upper-left 3×3 of inv_model^T)
+    let world_normal = normalize((obj.inv_model * vec4f(n, 0.0)).xyz);
+
+    var out: VertexOutput;
+    out.position       = clip_pos;
+    out.world_pos      = world_pos.xyz;
+    out.world_normal   = world_normal;
+    out.color          = obj.color;
+    out.instance_index = instance_index;
+    return out;
+}
+
+struct GBufOutput {
+    @location(0) albedo:     vec4f,  // rgba16float: material color
+    @location(1) normal_mat: vec4f,  // rgba16float: oct-normal XY in RG, mat_id/255 in B
+}
+
+@fragment
+fn fs_main(in: VertexOutput) -> GBufOutput {
+    let obj    = object_data.objects[in.instance_index];
+    let mat_id = f32(in.instance_index) / 255.0;
+
+    // Oct-encode world normal, remap [-1,1] → [0,1] for storage
+    let oct = oct_encode(normalize(in.world_normal)) * 0.5 + vec2f(0.5);
+
+    var out: GBufOutput;
+    out.albedo     = vec4f(in.color.rgb, 1.0);
+    out.normal_mat = vec4f(oct.x, oct.y, mat_id, 0.0);
+    return out;
+}