Merge branch 'main' into kpiascik/shadowtestassert

A zero color target fragment stage implies a depth pass by Filament.
We can create a pipeline without a fragment stage to make it valid.

BUGS=[421933134]

filament/backend/src/webgpu/WebGPUDriver.cpp

@@ -1215,12 +1215,6 @@ void WebGPUDriver::bindPipeline(PipelineState const& pipelineState) {
         }
     }
 
-    // TODO: We expected this to be a sane check, however it complains when running shadowtest.
-    //if (program->fragmentShaderModule != nullptr) {
-    //    FILAMENT_CHECK_POSTCONDITION(!pipelineColorFormats.empty())
-    //            << "Render pipeline with fragment shader must have at least one color target "
-    //               "format.";
-    //}
     wgpu::RenderPipeline pipeline = createWebGPURenderPipeline(mDevice, *program, *vertexBufferInfo,
             layout, pipelineState.rasterState, pipelineState.stencilState,
             pipelineState.polygonOffset, pipelineState.primitiveType, pipelineColorFormats,

filament/backend/src/webgpu/WebGPUPipelineCreation.cpp

@@ -281,6 +281,14 @@ wgpu::RenderPipeline createWebGPURenderPipeline(wgpu::Device const& device,
         }
     };
     if (program.fragmentShaderModule != nullptr) {
+        // According to the WebGPU spec, a pipeline cannot have a fragment stage with zero color
+        // targets. This situation can arise in Filament during depth-only passes (like shadow map
+        // generation) if the material variant still includes a fragment shader.
+        //
+        // To handle this, we check if any color targets are configured for this pipeline. If not, we
+        // create a pipeline *without* a fragment stage. This makes the pipeline valid for a
+        // depth-only pass, allowing depth writes to proceed correctly.
+        if (!colorFormats.empty()) {
             fragmentState.module = program.fragmentShaderModule;
             fragmentState.entryPoint = "main";
             // see the comment about constants for the vertex state, as the same reasoning applies
@@ -290,10 +298,6 @@ wgpu::RenderPipeline createWebGPURenderPipeline(wgpu::Device const& device,
             fragmentState.targetCount = colorFormats.size();
             fragmentState.targets = colorTargets.data();
             assert_invariant(fragmentState.targetCount <= MRT::MAX_SUPPORTED_RENDER_TARGET_COUNT);
-        // We expect a fragment shader implies at least one color target if it outputs color.
-        // This should be guaranteed by the caller ensuring colorFormats is not empty.
-        // However, this fails on shadowtest.cpp, TODO investigate why
-        // assert_invariant(fragmentState.targetCount > 0);
             for (size_t targetIndex = 0; targetIndex < fragmentState.targetCount; targetIndex++) {
                 auto& colorTarget = colorTargets[targetIndex];
                 colorTarget.format = colorFormats[targetIndex];
@@ -303,6 +307,7 @@ wgpu::RenderPipeline createWebGPURenderPipeline(wgpu::Device const& device,
             }
             pipelineDescriptor.fragment = &fragmentState;
         }
+    }
     const wgpu::RenderPipeline pipeline = device.CreateRenderPipeline(&pipelineDescriptor);
     FILAMENT_CHECK_POSTCONDITION(pipeline)
             << "Failed to create render pipeline for " << pipelineDescriptor.label;