feat(cnn_v3): GBufferEffect internal scene + GBufViewEffect debug wiring

GBufferEffect:
- set_scene() now owns Scene/Camera internally; no external pointers needed
- 20 randomly rotating cubes (xorshift32 seed, axis-angle animation)
- 4 pumping spheres (radius = base_r * (1 + audio_intensity * 0.8))
- Camera at (0,2.5,6) looking at origin; aspect updated per-frame
- GBufLightsUniforms: 2 directional lights (warm key + cool fill)
- object_type written to ObjectData.params.x (ready for SDF shadow)
- shadow/transp nodes cleared via zero-draw render passes (placeholder)
- bilinear sampler cached via create_linear_sampler() / sampler_.get()
- dead placeholder textures removed

GBufViewEffect:
- gbuf_view.wgsl: all channels now fully grayscale (removed color tint)
- seq_compiler.py: GBufViewEffect added to CLASS_TO_HEADER
- timeline.seq: cnn_v3_test uses GBufViewEffect -> sink for debug view

Docs: HOWTO.md §1 updated with set_scene() description + §1b implementation
plan for Pass 2 SDF shadow (shader spec, bind layout, C++ additions)

handoff(Gemini): GBufferEffect has internal scene, 36/36 tests green.
Next: implement Pass 2 shadow (gbuf_shadow.wgsl) per §1b plan in HOWTO.md.

2 files changed, 165 insertions, 83 deletions

diff --git a/cnn_v3/src/gbuffer_effect.cc b/cnn_v3/src/gbuffer_effect.cc
index 750188f..f529d2b 100644
--- a/cnn_v3/src/gbuffer_effect.cc
+++ b/cnn_v3/src/gbuffer_effect.cc
@@ -41,41 +41,6 @@ struct GBufGlobalUniforms {
 static_assert(sizeof(GBufGlobalUniforms) == sizeof(float) * 44,
               "GBufGlobalUniforms must be 176 bytes");
 
-// Helper: create a 1×1 placeholder texture of a given format cleared to `value`.
-static WGPUTexture create_placeholder_tex(WGPUDevice device,
-                                          WGPUTextureFormat format,
-                                          float value) {
-  WGPUTextureDescriptor desc = {};
-  desc.usage = (WGPUTextureUsage)(WGPUTextureUsage_TextureBinding |
-                                  WGPUTextureUsage_CopyDst);
-  desc.dimension = WGPUTextureDimension_2D;
-  desc.size = {1, 1, 1};
-  desc.format = format;
-  desc.mipLevelCount = 1;
-  desc.sampleCount = 1;
-  WGPUTexture tex = wgpuDeviceCreateTexture(device, &desc);
-  return tex;
-}
-
-// Helper: write a single RGBA float pixel to a texture via queue.
-static void write_placeholder_pixel(WGPUQueue queue, WGPUTexture tex,
-                                    float r, float g, float b, float a) {
-  const float data[4] = {r, g, b, a};
-  WGPUTexelCopyTextureInfo dst = {};
-  dst.texture = tex;
-  dst.mipLevel = 0;
-  dst.origin = {0, 0, 0};
-  dst.aspect = WGPUTextureAspect_All;
-
-  WGPUTexelCopyBufferLayout layout = {};
-  layout.offset = 0;
-  layout.bytesPerRow = 16; // 4 × sizeof(float)
-  layout.rowsPerImage = 1;
-
-  const WGPUExtent3D extent = {1, 1, 1};
-  wgpuQueueWriteTexture(queue, &dst, data, sizeof(data), &layout, &extent);
-}
-
 // Create bilinear sampler.
 static WGPUSampler create_bilinear_sampler(WGPUDevice device) {
   WGPUSamplerDescriptor desc = {};
@@ -116,31 +81,9 @@ GBufferEffect::GBufferEffect(const GpuContext& ctx,
 
   // Resolution uniform for pack shader.
   pack_res_uniform_.init(ctx_.device);
+  lights_uniform_.init(ctx_.device);
 
-  // Placeholder shadow (1.0 = fully lit) and transp (0.0 = opaque) textures.
-  shadow_placeholder_tex_.set(
-      create_placeholder_tex(ctx_.device, WGPUTextureFormat_RGBA32Float, 1.0f));
-  write_placeholder_pixel(ctx_.queue,
-                          shadow_placeholder_tex_.get(), 1.0f, 0.0f, 0.0f, 1.0f);
-
-  transp_placeholder_tex_.set(
-      create_placeholder_tex(ctx_.device, WGPUTextureFormat_RGBA32Float, 0.0f));
-  write_placeholder_pixel(ctx_.queue,
-                          transp_placeholder_tex_.get(), 0.0f, 0.0f, 0.0f, 1.0f);
-
-  WGPUTextureViewDescriptor vd = {};
-  vd.format = WGPUTextureFormat_RGBA32Float;
-  vd.dimension = WGPUTextureViewDimension_2D;
-  vd.baseMipLevel = 0;
-  vd.mipLevelCount = 1;
-  vd.baseArrayLayer = 0;
-  vd.arrayLayerCount = 1;
-  vd.aspect = WGPUTextureAspect_All;
-
-  shadow_placeholder_view_.set(
-      wgpuTextureCreateView(shadow_placeholder_tex_.get(), &vd));
-  transp_placeholder_view_.set(
-      wgpuTextureCreateView(transp_placeholder_tex_.get(), &vd));
+  create_linear_sampler();
 
   create_raster_pipeline();
   create_pack_pipeline();
@@ -162,19 +105,113 @@ void GBufferEffect::declare_nodes(NodeRegistry& registry) {
   }
 }
 
-void GBufferEffect::set_scene(const Scene* scene, const Camera* camera) {
-  scene_  = scene;
-  camera_ = camera;
+void GBufferEffect::set_scene() {
+  scene_.clear();
+  cube_anims_.clear();
+  sphere_anims_.clear();
+
+  // Deterministic pseudo-random (xorshift32).
+  uint32_t seed = 0xBEEF1234u;
+  auto rnd = [&]() -> float {
+    seed ^= seed << 13;
+    seed ^= seed >> 17;
+    seed ^= seed << 5;
+    return (float)(seed >> 8) / 16777216.0f;  // [0, 1)
+  };
+  auto rrange = [&](float lo, float hi) { return lo + rnd() * (hi - lo); };
+
+  // 20 small cubes scattered in a [-2,2]×[-1.5,1.5]×[-1.5,1.5] volume.
+  static const int kNumCubes = 20;
+  for (int i = 0; i < kNumCubes; ++i) {
+    Object3D obj(ObjectType::CUBE);
+    obj.position = vec3(rrange(-2.0f, 2.0f),
+                        rrange(-1.5f, 1.5f),
+                        rrange(-1.5f, 1.5f));
+    const float s = rrange(0.10f, 0.25f);
+    obj.scale = vec3(s, s, s);
+    obj.color = vec4(rrange(0.4f, 1.0f),
+                     rrange(0.4f, 1.0f),
+                     rrange(0.4f, 1.0f), 1.0f);
+
+    // Random rotation axis (avoid degenerate zero-length axis).
+    vec3 axis = vec3(rrange(-1.0f, 1.0f),
+                     rrange(-1.0f, 1.0f),
+                     rrange(-1.0f, 1.0f));
+    if (axis.len() < 0.01f) axis = vec3(0.0f, 1.0f, 0.0f);
+    axis = axis.normalize();
+    const float speed = rrange(0.3f, 1.5f) * (rnd() > 0.5f ? 1.0f : -1.0f);
+
+    scene_.add_object(obj);
+    cube_anims_.push_back({axis, speed});
+  }
+
+  // 4 pumping spheres at fixed positions; radius modulated by audio_intensity.
+  static const vec3 kSpherePos[4] = {
+    { 0.0f,  0.0f,  0.0f},
+    { 1.5f,  0.5f, -0.5f},
+    {-1.5f, -0.5f,  0.5f},
+    { 0.0f,  1.0f,  1.0f},
+  };
+  static const float kBaseSphereRadius[4] = {0.35f, 0.28f, 0.30f, 0.25f};
+  for (int i = 0; i < 4; ++i) {
+    Object3D obj(ObjectType::SPHERE);
+    obj.position = kSpherePos[i];
+    const float r = kBaseSphereRadius[i];
+    obj.scale = vec3(r, r, r);
+    obj.color = vec4(0.85f, 0.60f, 0.95f, 1.0f);
+    const int idx = (int)scene_.objects.size();
+    scene_.add_object(obj);
+    sphere_anims_.push_back({idx, r});
+  }
+
+  // Camera: above and in front of the scene, looking at origin.
+  camera_.set_look_at(vec3(0.0f, 2.5f, 6.0f),
+                      vec3(0.0f, 0.0f, 0.0f),
+                      vec3(0.0f, 1.0f, 0.0f));
+  camera_.fov_y_rad  = 0.7854f;  // 45°
+  camera_.near_plane = 0.1f;
+  camera_.far_plane  = 20.0f;
+  // aspect_ratio is updated each frame from params.resolution.
+
+  scene_ready_ = true;
 }
 
 void GBufferEffect::render(WGPUCommandEncoder encoder,
                            const UniformsSequenceParams& params,
                            NodeRegistry& nodes) {
-  if (!scene_ || !camera_) {
+  if (!scene_ready_) {
     return;
   }
 
-  upload_scene_data(*scene_, *camera_, params.time);
+  // Update camera aspect ratio from current resolution.
+  camera_.aspect_ratio = params.aspect_ratio;
+
+  // Animate cubes: axis-angle rotation driven by physical time.
+  for (int i = 0; i < (int)cube_anims_.size(); ++i) {
+    const CubeAnim& a = cube_anims_[(size_t)i];
+    scene_.objects[(size_t)i].rotation =
+        quat::from_axis(a.axis, params.time * a.speed);
+  }
+  // Pump spheres: scale with audio_intensity.
+  for (const SphereAnim& a : sphere_anims_) {
+    const float r = a.base_radius * (1.0f + params.audio_intensity * 0.8f);
+    scene_.objects[(size_t)a.obj_idx].scale = vec3(r, r, r);
+  }
+
+  // Upload two directional lights.
+  {
+    GBufLightsUniforms lu = {};
+    lu.params = vec4(2.0f, 0.0f, 0.0f, 0.0f);
+    // Key: warm sun, upper-right-front.
+    lu.lights[0].direction = vec4(0.408f, 0.816f, 0.408f, 0.0f);  // norm(1,2,1)
+    lu.lights[0].color     = vec4(1.00f, 0.92f, 0.78f, 1.0f);
+    // Fill: cool sky, upper-left-back.
+    lu.lights[1].direction = vec4(-0.577f, 0.577f, -0.577f, 0.0f);  // norm(-1,1,-1)
+    lu.lights[1].color     = vec4(0.40f, 0.45f, 0.80f, 0.4f);
+    lights_uniform_.update(ctx_.queue, lu);
+  }
+
+  upload_scene_data(scene_, camera_, params.time);
 
   // Update resolution uniform for pack shader.
   GBufResUniforms res_uni;
@@ -228,8 +265,8 @@ void GBufferEffect::render(WGPUCommandEncoder encoder,
   raster_pass_desc.depthStencilAttachment = &depth_attachment;
 
   const int num_objects =
-      (int)(scene_->objects.size() < (size_t)kGBufMaxObjects
-                ? scene_->objects.size()
+      (int)(scene_.objects.size() < (size_t)kGBufMaxObjects
+                ? scene_.objects.size()
                 : (size_t)kGBufMaxObjects);
 
   if (num_objects > 0 && raster_pipeline_.get() != nullptr) {
@@ -250,13 +287,31 @@ void GBufferEffect::render(WGPUCommandEncoder encoder,
     wgpuRenderPassEncoderRelease(raster_pass);
   }
 
-  // Pass 2: SDF raymarching — TODO (placeholder: shadow=1, transp=0 already set)
+  // Pass 2: SDF raymarching — TODO
   // Pass 3: Lighting/shadow — TODO
 
+  // Clear shadow node to 1.0 (fully lit) and transp to 0.0 (fully opaque)
+  // until passes 2-3 are implemented.
+  auto clear_node = [&](const std::string& name, float value) {
+    WGPURenderPassColorAttachment att = {};
+    att.view       = nodes.get_view(name);
+    att.loadOp     = WGPULoadOp_Clear;
+    att.storeOp    = WGPUStoreOp_Store;
+    att.clearValue = {value, value, value, value};
+    att.depthSlice = WGPU_DEPTH_SLICE_UNDEFINED;
+    WGPURenderPassDescriptor pd = {};
+    pd.colorAttachmentCount = 1;
+    pd.colorAttachments     = &att;
+    WGPURenderPassEncoder p = wgpuCommandEncoderBeginRenderPass(encoder, &pd);
+    wgpuRenderPassEncoderEnd(p);
+    wgpuRenderPassEncoderRelease(p);
+  };
+  clear_node(node_shadow_, 1.0f);
+  clear_node(node_transp_, 0.0f);
+
   // --- Pass 4: Pack compute ---
   // Rebuild pack bind group with current node views.
-  // Construct a temporary bilinear sampler for this pass.
-  WGPUSampler bilinear = create_bilinear_sampler(ctx_.device);
+  WGPUSampler bilinear = sampler_.get();
 
   // Get texture views from nodes.
   // shadow / transp are GBUF_R8 nodes; use their views.
@@ -320,7 +375,7 @@ void GBufferEffect::render(WGPUCommandEncoder encoder,
   wgpuComputePassEncoderRelease(compute_pass);
 
   wgpuBindGroupRelease(pack_bg);
-  wgpuSamplerRelease(bilinear);
+  // bilinear is owned by sampler_ — no release here.
 }
 
 // ---- private helpers ----
@@ -373,7 +428,7 @@ void GBufferEffect::upload_scene_data(const Scene& scene,
       d.model     = m;
       d.inv_model = m.inverse();
       d.color     = obj.color;
-      d.params    = vec4(0.0f, 0.0f, 0.0f, 0.0f);
+      d.params    = vec4((float)(int)obj.type, 0.0f, 0.0f, 0.0f);
       obj_data.push_back(d);
     }
     wgpuQueueWriteBuffer(ctx_.queue, objects_buf_.buffer, 0,
diff --git a/cnn_v3/src/gbuffer_effect.h b/cnn_v3/src/gbuffer_effect.h
index 42fb0ec..d45be75 100644
--- a/cnn_v3/src/gbuffer_effect.h
+++ b/cnn_v3/src/gbuffer_effect.h
@@ -10,6 +10,7 @@
 #include "gpu/uniform_helper.h"
 #include "gpu/wgpu_resource.h"
 #include "util/mini_math.h"
+#include <vector>
 
 // Uniform for the pack compute shader
 struct GBufResUniforms {
@@ -20,6 +21,20 @@ struct GBufResUniforms {
 static_assert(sizeof(GBufResUniforms) == 16,
               "GBufResUniforms must be 16 bytes");
 
+// Single directional light: direction points *toward* the light source (world space).
+struct GBufLight {
+  vec4 direction;  // xyz = normalized direction toward light, w = unused
+  vec4 color;      // rgb = color, a = intensity
+};
+static_assert(sizeof(GBufLight) == 32, "GBufLight must be 32 bytes");
+
+struct GBufLightsUniforms {
+  GBufLight lights[2];
+  vec4      params;  // x = num_lights
+};
+static_assert(sizeof(GBufLightsUniforms) == 80,
+              "GBufLightsUniforms must be 80 bytes");
+
 class GBufferEffect : public Effect {
  public:
   GBufferEffect(const GpuContext& ctx, const std::vector<std::string>& inputs,
@@ -31,9 +46,22 @@ class GBufferEffect : public Effect {
   void render(WGPUCommandEncoder encoder, const UniformsSequenceParams& params,
               NodeRegistry& nodes) override;
 
-  void set_scene(const Scene* scene, const Camera* camera);
+  // Populate the internal scene with ~20 rotating cubes and a few pumping
+  // spheres.  Must be called once before the first render().
+  void set_scene();
 
  private:
+  // Per-cube animation state (axis-angle rotation)
+  struct CubeAnim {
+    vec3  axis;
+    float speed;  // radians/second, may be negative
+  };
+  // Per-sphere animation state (radius driven by audio_intensity)
+  struct SphereAnim {
+    int   obj_idx;     // index into scene_.objects
+    float base_radius;
+  };
+
   // Internal G-buffer node names
   std::string node_albedo_;
   std::string node_normal_mat_;
@@ -43,8 +71,13 @@ class GBufferEffect : public Effect {
   std::string node_feat0_;
   std::string node_feat1_;
 
-  const Scene*  scene_  = nullptr;
-  const Camera* camera_ = nullptr;
+  // Owned scene and camera — populated by set_scene()
+  Scene  scene_;
+  Camera camera_;
+  bool   scene_ready_ = false;
+
+  std::vector<CubeAnim>  cube_anims_;
+  std::vector<SphereAnim> sphere_anims_;
 
   // Pass 1: MRT rasterization pipeline
   RenderPipeline raster_pipeline_;
@@ -53,19 +86,13 @@ class GBufferEffect : public Effect {
   // 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_;
+  UniformBuffer<GBufResUniforms>    pack_res_uniform_;
+  UniformBuffer<GBufLightsUniforms> lights_uniform_;
 
   // 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
+  int       objects_buf_capacity_ = 0;
 
   void create_raster_pipeline();
   void create_pack_pipeline();