refactor(gpu): move RenderPipelineBuilder impl to pipeline_builder.cc

Keeps .h as declarations only; moves all method bodies to .cc.
Adds pipeline_builder.cc to COMMON_GPU_EFFECTS in DemoSourceLists.cmake.

handoff(Claude): pipeline_builder split to .h/.cc, builds clean.

1 files changed, 91 insertions, 0 deletions

diff --git a/src/gpu/pipeline_builder.cc b/src/gpu/pipeline_builder.cc
new file mode 100644
index 0000000..b3fa5f8
--- /dev/null
+++ b/src/gpu/pipeline_builder.cc
@@ -0,0 +1,91 @@
+// WGPU render pipeline builder - implementation
+#include "gpu/pipeline_builder.h"
+#include "util/fatal_error.h"
+
+RenderPipelineBuilder::RenderPipelineBuilder(WGPUDevice device)
+    : device_(device) {
+  desc_.primitive.topology = WGPUPrimitiveTopology_TriangleList;
+  desc_.primitive.cullMode = WGPUCullMode_None;
+  desc_.multisample.count = 1;
+  desc_.multisample.mask = 0xFFFFFFFF;
+}
+
+RenderPipelineBuilder& RenderPipelineBuilder::shader(const char* wgsl,
+                                                      bool compose) {
+  shader_text_ = compose ? ShaderComposer::Get().Compose({}, wgsl) : wgsl;
+  if (device_ == nullptr)
+    return *this;
+  WGPUShaderSourceWGSL wgsl_src{};
+  wgsl_src.chain.sType = WGPUSType_ShaderSourceWGSL;
+  wgsl_src.code = str_view(shader_text_.c_str());
+  WGPUShaderModuleDescriptor shader_desc{};
+  shader_desc.nextInChain = &wgsl_src.chain;
+  shader_module_ = wgpuDeviceCreateShaderModule(device_, &shader_desc);
+  desc_.vertex.module = shader_module_;
+  desc_.vertex.entryPoint = str_view("vs_main");
+  return *this;
+}
+
+RenderPipelineBuilder& RenderPipelineBuilder::bind_group_layout(
+    WGPUBindGroupLayout layout) {
+  layouts_.push_back(layout);
+  return *this;
+}
+
+RenderPipelineBuilder& RenderPipelineBuilder::format(WGPUTextureFormat fmt) {
+  color_.format = fmt;
+  return *this;
+}
+
+RenderPipelineBuilder& RenderPipelineBuilder::blend_alpha() {
+  has_blend_ = true;
+  blend_.color.operation = WGPUBlendOperation_Add;
+  blend_.color.srcFactor = WGPUBlendFactor_SrcAlpha;
+  blend_.color.dstFactor = WGPUBlendFactor_OneMinusSrcAlpha;
+  blend_.alpha.operation = WGPUBlendOperation_Add;
+  blend_.alpha.srcFactor = WGPUBlendFactor_One;
+  blend_.alpha.dstFactor = WGPUBlendFactor_OneMinusSrcAlpha;
+  return *this;
+}
+
+RenderPipelineBuilder& RenderPipelineBuilder::depth(
+    WGPUTextureFormat depth_fmt) {
+  has_depth_ = true;
+  depth_.format = depth_fmt;
+  depth_.depthWriteEnabled = WGPUOptionalBool_True;
+  depth_.depthCompare = WGPUCompareFunction_Less;
+  return *this;
+}
+
+RenderPipelineBuilder& RenderPipelineBuilder::cull_back() {
+  desc_.primitive.cullMode = WGPUCullMode_Back;
+  return *this;
+}
+
+WGPURenderPipeline RenderPipelineBuilder::build() {
+  HEADLESS_RETURN_VAL_IF_NULL(device_, nullptr);
+
+  color_.writeMask = WGPUColorWriteMask_All;
+  if (has_blend_)
+    color_.blend = &blend_;
+
+  WGPUFragmentState fragment{};
+  fragment.module = shader_module_;
+  fragment.entryPoint = str_view("fs_main");
+  fragment.targetCount = 1;
+  fragment.targets = &color_;
+
+  WGPUPipelineLayoutDescriptor pl_desc{};
+  pl_desc.bindGroupLayoutCount = layouts_.size();
+  pl_desc.bindGroupLayouts = layouts_.data();
+  WGPUPipelineLayout layout = wgpuDeviceCreatePipelineLayout(device_, &pl_desc);
+
+  desc_.layout = layout;
+  desc_.fragment = &fragment;
+  if (has_depth_)
+    desc_.depthStencil = &depth_;
+
+  WGPURenderPipeline pipeline = wgpuDeviceCreateRenderPipeline(device_, &desc_);
+  wgpuPipelineLayoutRelease(layout);
+  return pipeline;
+}