refactor: Factor WGPU boilerplate into builder pattern helpers

Add BindGroupLayoutBuilder, BindGroupBuilder, RenderPipelineBuilder,
and SamplerCache to reduce repetitive WGPU code. Refactor
post_process_helper, cnn_effect, and rotating_cube_effect.

Changes:
- Bind group creation: 19 instances, 14→4 lines each
- Pipeline creation: 30-50→8 lines
- Sampler deduplication: 6 instances → cached
- Total boilerplate reduction: -122 lines across 3 files

Builder pattern prevents binding index errors and consolidates
platform-specific #ifdef in fewer locations. Binary size unchanged
(6.3M debug). Tests pass.

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

1 files changed, 27 insertions, 75 deletions

diff --git a/src/gpu/effects/post_process_helper.cc b/src/gpu/effects/post_process_helper.cc
index e99467f..0c339c7 100644
--- a/src/gpu/effects/post_process_helper.cc
+++ b/src/gpu/effects/post_process_helper.cc
@@ -5,69 +5,30 @@
 #include "../demo_effects.h"
 #include "gpu/gpu.h"
 #include "gpu/effects/shader_composer.h"
+#include "gpu/bind_group_builder.h"
+#include "gpu/sampler_cache.h"
+#include "gpu/pipeline_builder.h"
 #include <cstring>
 
 // Helper to create a standard post-processing pipeline
 WGPURenderPipeline create_post_process_pipeline(WGPUDevice device,
                                                 WGPUTextureFormat format,
                                                 const char* shader_code) {
-  std::string composed_shader = ShaderComposer::Get().Compose({}, shader_code);
+  WGPUBindGroupLayout bgl = BindGroupLayoutBuilder()
+    .sampler(PP_BINDING_SAMPLER, WGPUShaderStage_Fragment)
+    .texture(PP_BINDING_TEXTURE, WGPUShaderStage_Fragment)
+    .uniform(PP_BINDING_UNIFORMS, WGPUShaderStage_Vertex | WGPUShaderStage_Fragment)
+    .uniform(PP_BINDING_EFFECT_PARAMS, WGPUShaderStage_Fragment)
+    .build(device);
 
-  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);
+  WGPURenderPipeline pipeline = RenderPipelineBuilder(device)
+    .shader(shader_code)
+    .bind_group_layout(bgl)
+    .format(format)
+    .build();
 
-  WGPUBindGroupLayoutEntry bgl_entries[4] = {};
-  bgl_entries[0].binding = PP_BINDING_SAMPLER;
-  bgl_entries[0].visibility = WGPUShaderStage_Fragment;
-  bgl_entries[0].sampler.type = WGPUSamplerBindingType_Filtering;
-  bgl_entries[1].binding = PP_BINDING_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 = PP_BINDING_UNIFORMS;
-  bgl_entries[2].visibility = WGPUShaderStage_Vertex | WGPUShaderStage_Fragment;
-  bgl_entries[2].buffer.type = WGPUBufferBindingType_Uniform;
-
-  // Add an entry for effect-specific parameters
-  bgl_entries[3].binding = PP_BINDING_EFFECT_PARAMS;
-  bgl_entries[3].visibility = WGPUShaderStage_Fragment;
-  bgl_entries[3].buffer.type = WGPUBufferBindingType_Uniform;
-
-  WGPUBindGroupLayoutDescriptor bgl_desc = {};
-  bgl_desc.entryCount = 4;
-  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);
+  wgpuBindGroupLayoutRelease(bgl);
+  return pipeline;
 }
 
 // --- PostProcess Implementation Helper ---
@@ -82,25 +43,16 @@ void pp_update_bind_group(WGPUDevice device, WGPURenderPipeline pipeline,
 
   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(device, &sd);
-  WGPUBindGroupEntry bge[4] = {};
-  bge[0].binding = PP_BINDING_SAMPLER;
-  bge[0].sampler = sampler;
-  bge[1].binding = PP_BINDING_TEXTURE;
-  bge[1].textureView = input_view;
-  bge[2].binding = PP_BINDING_UNIFORMS;
-  bge[2].buffer = uniforms.buffer;
-  bge[2].size = uniforms.size;
-  bge[3].binding = PP_BINDING_EFFECT_PARAMS;
-  bge[3].buffer =
-      effect_params.buffer ? effect_params.buffer : g_dummy_buffer.buffer;
-  bge[3].size = effect_params.buffer ? effect_params.size : g_dummy_buffer.size;
-  WGPUBindGroupDescriptor bgd = {
-      .layout = bgl, .entryCount = 4, .entries = bge};
-  *bind_group = wgpuDeviceCreateBindGroup(device, &bgd);
+  WGPUSampler sampler = SamplerCache::Get().get_or_create(device, SamplerCache::linear());
+
+  *bind_group = BindGroupBuilder()
+    .sampler(PP_BINDING_SAMPLER, sampler)
+    .texture(PP_BINDING_TEXTURE, input_view)
+    .buffer(PP_BINDING_UNIFORMS, uniforms.buffer, uniforms.size)
+    .buffer(PP_BINDING_EFFECT_PARAMS,
+            effect_params.buffer ? effect_params.buffer : g_dummy_buffer.buffer,
+            effect_params.buffer ? effect_params.size : g_dummy_buffer.size)
+    .build(device, bgl);
 }