feat: Add multi-layer CNN support with framebuffer capture and blend control

Implements automatic layer chaining and generic framebuffer capture API for
multi-layer neural network effects with proper original input preservation.

Key changes:
- Effect::needs_framebuffer_capture() - generic API for pre-render capture
- MainSequence: auto-capture to "captured_frame" auxiliary texture
- CNNEffect: multi-layer support via layer_index/total_layers params
- seq_compiler: expands "layers=N" to N chained effect instances
- Shader: @binding(4) original_input available to all layers
- Training: generates layer switches and original input binding
- Blend: mix(original, result, blend_amount) uses layer 0 input

Timeline syntax: CNNEffect layers=3 blend=0.7

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 123 insertions, 7 deletions

diff --git a/src/gpu/effects/cnn_effect.cc b/src/gpu/effects/cnn_effect.cc
index 25db0c2..f5d0a51 100644
--- a/src/gpu/effects/cnn_effect.cc
+++ b/src/gpu/effects/cnn_effect.cc
@@ -4,19 +4,101 @@
 #include "gpu/effects/cnn_effect.h"
 #include "gpu/effects/post_process_helper.h"
 #include "gpu/effects/shaders.h"
+#include "gpu/effects/shader_composer.h"
+#include "gpu/effect.h"
 
-CNNEffect::CNNEffect(const GpuContext& ctx, int num_layers)
-    : PostProcessEffect(ctx), num_layers_(num_layers), input_view_(nullptr),
+// Create custom pipeline with 5 bindings (includes original texture)
+static WGPURenderPipeline create_cnn_pipeline(WGPUDevice device,
+                                               WGPUTextureFormat format,
+                                               const char* shader_code) {
+  std::string composed_shader = ShaderComposer::Get().Compose({}, shader_code);
+
+  WGPUShaderModuleDescriptor shader_desc = {};
+  WGPUShaderSourceWGSL wgsl_src = {};
+  wgsl_src.chain.sType = WGPUSType_ShaderSourceWGSL;
+  wgsl_src.code = str_view(composed_shader.c_str());
+  shader_desc.nextInChain = &wgsl_src.chain;
+  WGPUShaderModule shader_module =
+      wgpuDeviceCreateShaderModule(device, &shader_desc);
+
+  WGPUBindGroupLayoutEntry bgl_entries[5] = {};
+  bgl_entries[0].binding = 0; // sampler
+  bgl_entries[0].visibility = WGPUShaderStage_Fragment;
+  bgl_entries[0].sampler.type = WGPUSamplerBindingType_Filtering;
+  bgl_entries[1].binding = 1; // input texture
+  bgl_entries[1].visibility = WGPUShaderStage_Fragment;
+  bgl_entries[1].texture.sampleType = WGPUTextureSampleType_Float;
+  bgl_entries[1].texture.viewDimension = WGPUTextureViewDimension_2D;
+  bgl_entries[2].binding = 2; // uniforms
+  bgl_entries[2].visibility = WGPUShaderStage_Vertex | WGPUShaderStage_Fragment;
+  bgl_entries[2].buffer.type = WGPUBufferBindingType_Uniform;
+  bgl_entries[3].binding = 3; // effect params
+  bgl_entries[3].visibility = WGPUShaderStage_Fragment;
+  bgl_entries[3].buffer.type = WGPUBufferBindingType_Uniform;
+  bgl_entries[4].binding = 4; // original texture
+  bgl_entries[4].visibility = WGPUShaderStage_Fragment;
+  bgl_entries[4].texture.sampleType = WGPUTextureSampleType_Float;
+  bgl_entries[4].texture.viewDimension = WGPUTextureViewDimension_2D;
+
+  WGPUBindGroupLayoutDescriptor bgl_desc = {};
+  bgl_desc.entryCount = 5;
+  bgl_desc.entries = bgl_entries;
+  WGPUBindGroupLayout bgl = wgpuDeviceCreateBindGroupLayout(device, &bgl_desc);
+
+  WGPUPipelineLayoutDescriptor pl_desc = {};
+  pl_desc.bindGroupLayoutCount = 1;
+  pl_desc.bindGroupLayouts = &bgl;
+  WGPUPipelineLayout pl = wgpuDeviceCreatePipelineLayout(device, &pl_desc);
+
+  WGPUColorTargetState color_target = {};
+  color_target.format = format;
+  color_target.writeMask = WGPUColorWriteMask_All;
+
+  WGPUFragmentState fragment_state = {};
+  fragment_state.module = shader_module;
+  fragment_state.entryPoint = str_view("fs_main");
+  fragment_state.targetCount = 1;
+  fragment_state.targets = &color_target;
+
+  WGPURenderPipelineDescriptor pipeline_desc = {};
+  pipeline_desc.layout = pl;
+  pipeline_desc.vertex.module = shader_module;
+  pipeline_desc.vertex.entryPoint = str_view("vs_main");
+  pipeline_desc.fragment = &fragment_state;
+  pipeline_desc.primitive.topology = WGPUPrimitiveTopology_TriangleList;
+  pipeline_desc.multisample.count = 1;
+  pipeline_desc.multisample.mask = 0xFFFFFFFF;
+
+  return wgpuDeviceCreateRenderPipeline(device, &pipeline_desc);
+}
+
+CNNEffect::CNNEffect(const GpuContext& ctx)
+    : PostProcessEffect(ctx), layer_index_(0), total_layers_(1),
+      blend_amount_(1.0f), input_view_(nullptr), original_view_(nullptr),
       bind_group_(nullptr) {
-  pipeline_ = create_post_process_pipeline(ctx_.device, ctx_.format,
-                                           cnn_layer_shader_wgsl);
+  pipeline_ = create_cnn_pipeline(ctx_.device, ctx_.format,
+                                  cnn_layer_shader_wgsl);
+}
+
+CNNEffect::CNNEffect(const GpuContext& ctx, const CNNEffectParams& params)
+    : PostProcessEffect(ctx), layer_index_(params.layer_index),
+      total_layers_(params.total_layers), blend_amount_(params.blend_amount),
+      input_view_(nullptr), original_view_(nullptr), bind_group_(nullptr) {
+  pipeline_ = create_cnn_pipeline(ctx_.device, ctx_.format,
+                                  cnn_layer_shader_wgsl);
 }
 
 void CNNEffect::init(MainSequence* demo) {
   PostProcessEffect::init(demo);
+  demo_ = demo;
   params_buffer_.init(ctx_.device);
 
-  CNNLayerParams params = {0, 1, {0.0f, 0.0f}};
+  // Register captured_frame texture (used by all layers for original input)
+  if (layer_index_ == 0) {
+    demo_->register_auxiliary_texture("captured_frame", width_, height_);
+  }
+
+  CNNLayerParams params = {layer_index_, blend_amount_, {0.0f, 0.0f}};
   params_buffer_.update(ctx_.queue, params);
 }
 
@@ -31,6 +113,40 @@ void CNNEffect::render(WGPURenderPassEncoder pass, float time, float beat,
 
 void CNNEffect::update_bind_group(WGPUTextureView input_view) {
   input_view_ = input_view;
-  pp_update_bind_group(ctx_.device, pipeline_, &bind_group_,
-                      input_view_, uniforms_.get(), params_buffer_.get());
+
+  // All layers: get captured frame (original input from layer 0)
+  if (demo_) {
+    original_view_ = demo_->get_auxiliary_view("captured_frame");
+  }
+
+  // Create bind group with original texture
+  if (bind_group_)
+    wgpuBindGroupRelease(bind_group_);
+
+  WGPUBindGroupLayout bgl = wgpuRenderPipelineGetBindGroupLayout(pipeline_, 0);
+  WGPUSamplerDescriptor sd = {};
+  sd.magFilter = WGPUFilterMode_Linear;
+  sd.minFilter = WGPUFilterMode_Linear;
+  sd.maxAnisotropy = 1;
+  WGPUSampler sampler = wgpuDeviceCreateSampler(ctx_.device, &sd);
+
+  WGPUBindGroupEntry bge[5] = {};
+  bge[0].binding = 0;
+  bge[0].sampler = sampler;
+  bge[1].binding = 1;
+  bge[1].textureView = input_view_;
+  bge[2].binding = 2;
+  bge[2].buffer = uniforms_.get().buffer;
+  bge[2].size = uniforms_.get().size;
+  bge[3].binding = 3;
+  bge[3].buffer = params_buffer_.get().buffer;
+  bge[3].size = params_buffer_.get().size;
+  bge[4].binding = 4;
+  bge[4].textureView = original_view_ ? original_view_ : input_view_; // Fallback
+
+  WGPUBindGroupDescriptor bgd = {};
+  bgd.layout = bgl;
+  bgd.entryCount = 5;
+  bgd.entries = bge;
+  bind_group_ = wgpuDeviceCreateBindGroup(ctx_.device, &bgd);
 }