feat(gpu): Systematize post-process bindings and enable vertex shader uniforms

- Add PP_BINDING_* macros for standard post-process bind group layout
  - PP_BINDING_SAMPLER (0): Input texture sampler
  - PP_BINDING_TEXTURE (1): Input texture from previous pass
  - PP_BINDING_UNIFORMS (2): Custom uniforms buffer
- Change uniforms visibility from Fragment-only to Vertex|Fragment
  - Enables dynamic geometry in vertex shaders (e.g., peak meter bar)
- Replace all hardcoded binding numbers with macros in post_process_helper.cc
- Update test_demo.cc to use systematic bindings
- Benefits: All post-process effects can now access uniforms in vertex shaders

Result: More flexible post-process effects, better code maintainability

1 files changed, 8 insertions, 7 deletions

diff --git a/src/gpu/effects/post_process_helper.cc b/src/gpu/effects/post_process_helper.cc
index db89d77..0a2ac22 100644
--- a/src/gpu/effects/post_process_helper.cc
+++ b/src/gpu/effects/post_process_helper.cc
@@ -1,6 +1,7 @@
 // This file is part of the 64k demo project.
 // It implements helper functions for post-processing effects.
 
+#include "post_process_helper.h"
 #include "../demo_effects.h"
 #include "gpu/gpu.h"
 #include <cstring>
@@ -18,15 +19,15 @@ WGPURenderPipeline create_post_process_pipeline(WGPUDevice device,
       wgpuDeviceCreateShaderModule(device, &shader_desc);
 
   WGPUBindGroupLayoutEntry bgl_entries[3] = {};
-  bgl_entries[0].binding = 0;
+  bgl_entries[0].binding = PP_BINDING_SAMPLER;
   bgl_entries[0].visibility = WGPUShaderStage_Fragment;
   bgl_entries[0].sampler.type = WGPUSamplerBindingType_Filtering;
-  bgl_entries[1].binding = 1;
+  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 = 2;
-  bgl_entries[2].visibility = WGPUShaderStage_Fragment;
+  bgl_entries[2].binding = PP_BINDING_UNIFORMS;
+  bgl_entries[2].visibility = WGPUShaderStage_Vertex | WGPUShaderStage_Fragment;
   bgl_entries[2].buffer.type = WGPUBufferBindingType_Uniform;
 
   WGPUBindGroupLayoutDescriptor bgl_desc = {};
@@ -74,11 +75,11 @@ void pp_update_bind_group(WGPUDevice device, WGPURenderPipeline pipeline,
   sd.maxAnisotropy = 1;
   WGPUSampler sampler = wgpuDeviceCreateSampler(device, &sd);
   WGPUBindGroupEntry bge[3] = {};
-  bge[0].binding = 0;
+  bge[0].binding = PP_BINDING_SAMPLER;
   bge[0].sampler = sampler;
-  bge[1].binding = 1;
+  bge[1].binding = PP_BINDING_TEXTURE;
   bge[1].textureView = input_view;
-  bge[2].binding = 2;
+  bge[2].binding = PP_BINDING_UNIFORMS;
   bge[2].buffer = uniforms.buffer;
   bge[2].size = uniforms.size;
   WGPUBindGroupDescriptor bgd = {