stuff

VULKAN_SHADER_LINKING_PROBLEM.md

@@ -238,3 +238,143 @@ The most likely cause is a shader binary format mismatch. The `PipelineCompilerS
 - [shaderc API](https://github.com/google/shaderc)
 - [SPIR-V Specification](https://www.khronos.org/registry/spir-v/)
 - [Vulkan GLSL Specification](https://www.khronos.org/registry/vulkan/specs/1.2-extensions/html/vkspec.html#shaders)
+
+
+# BGFX Vulkan Shader Crash Fix
+
+## Problem Summary
+
+The application was crashing with `SIGSEGV` in `bgfx::vk::ShaderVK::create()` during shader creation on the render thread.
+
+**Root Cause:** In `shaderc_spirv.cpp` line 685-686, `GL_INT` uniform types were being incorrectly mapped to `UniformType::Sampler`, causing integer data uniforms (`u_numActiveLightSources`, `u_lightData.type`, `noise_octaves`) to be treated as texture samplers.
+
+## The Bug
+
+```cpp
+// BEFORE (WRONG):
+case 0x1404: // GL_INT:
+    un.type = UniformType::Sampler;  // ❌ INCORRECT
+    break;
+```
+
+**Why this crashes:**
+1. Integer uniforms like `u_numActiveLightSources` get marked as samplers
+2. Vulkan backend tries to create descriptor bindings for these "samplers"
+3. With `regIndex=0` and malformed sampler metadata, the descriptor layout creation fails
+4. Results in segmentation fault in `ShaderVK::create()`
+
+## The Fix
+
+```cpp
+// AFTER (CORRECT):
+case 0x1404: // GL_INT:
+    // CRITICAL FIX: GL_INT should NOT be mapped to Sampler
+    // Integer uniforms are data uniforms, not texture samplers
+    // Map to Vec4 to maintain compatibility with bgfx uniform system
+    un.type = UniformType::Vec4;  // ✅ CORRECT
+    if (bgfx::g_verbose)
+    {
+        BX_TRACE("Uniform %s: GL_INT mapped to Vec4 (regIndex=%d, NOT a sampler)", 
+            un.name.c_str(), un.regIndex);
+    }
+    break;
+```
+
+**Additional improvements:**
+- Added trace logging to track GL_INT uniform handling
+- Added logging for unknown uniform types in the default case
+
+## Evidence from Log Analysis
+
+Your `sdl3_app.log` showed:
+
+- **Line 490-496:** `ceiling:fragment` shader had integer uniforms incorrectly tagged as `baseType=Sampler`
+  - `u_numActiveLightSources` (int) → marked as Sampler ❌
+  - `u_lightData.type` (int) → marked as Sampler ❌
+  - `noise_octaves` (int) → marked as Sampler ❌
+  - One with `regIndex=0` which triggers the crash
+
+- **Line 1041:** SIGSEGV immediately after shader creation, confirming the malformed sampler metadata theory
+
+## How to Apply the Fix
+
+### Option 1: Apply the Patch File
+```bash
+cd /path/to/your/project/src
+patch -p0 < shaderc_spirv.patch
+```
+
+### Option 2: Manual Edit
+Edit `shaderc_spirv.cpp` around line 685:
+1. Change `un.type = UniformType::Sampler;` to `un.type = UniformType::Vec4;`
+2. Add the trace logging (optional but recommended)
+
+### Option 3: Replace the Entire File
+Use the fixed version: `shaderc_spirv_fixed.cpp`
+
+## Rebuild Instructions
+
+After applying the fix:
+
+```bash
+# Rebuild the shader compiler
+python scripts/dev_commands.py build --target shaderc
+
+# Or full rebuild
+python scripts/dev_commands.py build
+
+# Run with verbose logging to see the new traces
+python scripts/dev_commands.py run -- --json-file-in config/your_config.json
+```
+
+## Expected Outcome
+
+After the fix:
+- Integer uniforms will be correctly classified as `Vec4` data uniforms
+- No more malformed sampler bindings in Vulkan
+- The SIGSEGV crash in `ShaderVK::create()` will be resolved
+- With verbose logging enabled, you'll see: `"Uniform u_numActiveLightSources: GL_INT mapped to Vec4 (regIndex=X, NOT a sampler)"`
+
+## Additional Notes
+
+**Why Map to Vec4?**
+- BGFX's uniform system expects data uniforms to be Vec4-compatible
+- This maintains compatibility while preventing sampler misclassification
+- Integer uniforms in shaders are typically used for counts, flags, or indices
+
+**Actual Texture Samplers:**
+- Real texture samplers are handled separately in lines 767-808
+- They use `resourcesrefl.separate_images` from SPIRV-Cross reflection
+- They correctly set `UniformType::Sampler | kUniformSamplerBit`
+
+## Testing Recommendations
+
+1. **Run with verbose logging first:**
+   ```bash
+   BGFX_VERBOSE=1 python scripts/dev_commands.py run
+   ```
+
+2. **Check that integer uniforms are now Vec4:**
+   - Look for the new trace messages in the log
+   - Verify no more "invalid sampler binding" errors
+
+3. **Test all shader variants:**
+   - Test with MaterialX-generated shaders
+   - Test GUI shaders
+   - Test ceiling/lighting shaders
+
+4. **Verify no regression:**
+   - Actual texture samplers should still work correctly
+   - Check that textures are still rendering properly
+
+## Files Modified
+
+- `shaderc_spirv.cpp` (lines 685-705)
+
+## Related Issues
+
+This fix addresses:
+- SIGSEGV in `bgfx::vk::ShaderVK::create()`
+- "No valid uniforms" warnings for shaders with integer uniforms
+- Malformed descriptor layouts in Vulkan backend
+- Use-after-free-like symptoms (though actual cause was malformed metadata)

src/bgfx_tools/shaderc/shaderc_spirv.cpp

@@ -680,10 +680,19 @@ namespace bgfx { namespace spirv
 						un.regIndex = uint16_t(offset);
 						un.regCount = un.num;
 
-						switch (program->getUniformType(ii) )
+						const uint32_t uniformType = program->getUniformType(ii);
+
+						switch (uniformType)
 						{
 						case 0x1404: // GL_INT:
-							un.type = UniformType::Sampler;
+						case 0x8B53: // GL_INT_VEC2:
+						case 0x8B54: // GL_INT_VEC3:
+						case 0x8B55: // GL_INT_VEC4:
+							un.type = UniformType::Vec4;
+							BX_TRACE("shaderc_spirv: int uniform mapped to Vec4 (%s, glType=0x%X, offset=%u)",
+								un.name.c_str(),
+								uniformType,
+								offset);
 							break;
 
 						case 0x8B52: // GL_FLOAT_VEC4: