debug: Add shader load verification and GPU sync to CNN test tool

Debug additions:
- Print loaded shader size (confirms assets work: 2274 bytes)
- Add wgpuDevicePoll after each layer for GPU sync
- Verify shader loading with null/empty checks

Findings:
- Shader loads correctly (2274 bytes)
- GPU commands execute without validation errors
- Pipeline compiles successfully
- Output remains all-black despite correct architecture

Likely causes:
- Render setup differs from demo's CNNEffect
- Possible issue with bind group bindings
- Fragment shader may not be executing
- Texture sampling might be failing

Next steps:
- Create minimal solid-color render test
- Compare bind group setup with working CNNEffect
- Add fragment shader debug output (if possible)
- Test with demo's CNN effect to verify weights/shader work

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

1 files changed, 10 insertions, 0 deletions

diff --git a/tools/cnn_test.cc b/tools/cnn_test.cc
index bb4a824..c44606c 100644
--- a/tools/cnn_test.cc
+++ b/tools/cnn_test.cc
@@ -151,6 +151,13 @@ static WGPURenderPipeline create_cnn_pipeline(WGPUDevice device,
                                                bool is_final_layer) {
   const char* shader_code = SafeGetAsset(AssetId::ASSET_SHADER_CNN_LAYER);
 
+  // Debug: check if shader loaded
+  if (!shader_code || shader_code[0] == '\0') {
+    fprintf(stderr, "ERROR: CNN shader asset not loaded!\n");
+    return nullptr;
+  }
+  printf("Loaded CNN shader: %zu bytes\n", strlen(shader_code));
+
   WGPUBindGroupLayout bgl =
       BindGroupLayoutBuilder()
           .sampler(0, WGPUShaderStage_Fragment)
@@ -425,6 +432,9 @@ int main(int argc, char** argv) {
     WGPUCommandBuffer commands = wgpuCommandEncoderFinish(encoder, nullptr);
     wgpuQueueSubmit(queue, 1, &commands);
 
+    // Wait for GPU to complete this layer before proceeding
+    wgpuDevicePoll(device, true, nullptr);
+
     wgpuCommandBufferRelease(commands);
     wgpuRenderPassEncoderRelease(pass);
     wgpuCommandEncoderRelease(encoder);