feat(webgpu): WebGPU backend via Dawn, rebased onto v1.75.0

.github/workflows/build-filament.yml

@@ -34,6 +34,11 @@ on:
         required: false
         default: true
         type: boolean
+      webgpu:
+        description: 'Build Filament with FILAMENT_SUPPORTS_WEBGPU=ON (macOS, Linux)'
+        required: false
+        default: false
+        type: boolean
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}-${{ inputs.platform || 'all' }}
@@ -67,6 +72,21 @@ jobs:
           # Override individually if provided
           [ -n "${{ inputs.filament_repo }}" ] && REPO="${{ inputs.filament_repo }}"
           [ -n "${{ inputs.filament_version }}" ] && VERSION="${{ inputs.filament_version }}"
+          # Resolve VERSION=latest to the newest v*.* tag on the chosen repo.
+          # The per-platform jobs do `git clone --branch $VERSION` so we must
+          # produce a concrete tag here, not the literal string "latest".
+          if [ "$VERSION" = "latest" ]; then
+            echo "Resolving latest tag on $REPO..."
+            VERSION=$(git ls-remote --tags --refs --sort=-version:refname \
+              "$REPO" 'v*' \
+              | awk -F/ '{print $NF}' \
+              | head -1)
+            if [ -z "$VERSION" ]; then
+              echo "Error: could not resolve latest tag on $REPO"
+              exit 1
+            fi
+            echo "Resolved latest -> $VERSION"
+          fi
           echo "repo=$REPO" >> $GITHUB_OUTPUT
           echo "version=$VERSION" >> $GITHUB_OUTPUT
           echo "Building Filament repo: $REPO ref: $VERSION"
@@ -84,7 +104,10 @@ jobs:
 
   build-macos:
     name: Build macOS
-    runs-on: macos-14
+    # Xcode 16 (Clang 16+) is required for Dawn's use of C++20 parenthesized
+    # aggregate initialization (P0960). macos-14 ships Xcode 15.4 / Clang 15,
+    # which lacks P0960 and fails compiling third_party/dawn/src/dawn/platform.
+    runs-on: macos-15
     needs: setup
     if: contains(needs.setup.outputs.matrix, 'macos')
     env:
@@ -100,24 +123,57 @@ jobs:
       - name: Setup Ninja
         uses: seanmiddleditch/gha-setup-ninja@master
 
+      - name: Compute zip suffix
+        run: |
+          if [ "${{ inputs.webgpu }}" = "true" ]; then
+            echo "ZIP_SUFFIX=-webgpu" >> $GITHUB_ENV
+          else
+            echo "ZIP_SUFFIX=" >> $GITHUB_ENV
+          fi
+
+      - name: Free disk space
+        # The WebGPU build zips huge Dawn debug artifacts and ran out of disk
+        # (zip I/O error - No space left on device). jlumbroso/free-disk-space
+        # is Ubuntu-only, so delete the large preinstalled toolchains this
+        # build does not need: extra Xcode versions (keep the selected one),
+        # Android SDK/NDK, simulator runtimes, dotnet and ghcup.
+        run: |
+          df -h / | tail -1
+          SELECTED_XCODE=$(basename "$(dirname "$(dirname "$(xcode-select -p)")")")
+          echo "Keeping $SELECTED_XCODE"
+          for xcode in /Applications/Xcode*.app; do
+            if [ "$(basename "$xcode")" != "$SELECTED_XCODE" ]; then
+              echo "Removing $xcode"
+              sudo rm -rf "$xcode"
+            fi
+          done
+          sudo rm -rf /usr/local/lib/android /Users/runner/Library/Android
+          sudo rm -rf /Library/Developer/CoreSimulator /Users/runner/Library/Developer/CoreSimulator
+          sudo rm -rf /usr/local/share/dotnet /usr/local/.ghcup /usr/local/share/boost
+          df -h / | tail -1
+
       - name: Build Filament
         run: |
           mkdir -p output
           chmod +x scripts/build_macos.sh
-          scripts/build_macos.sh filament ${{ env.FILAMENT_VERSION }} output --clean
+          EXTRA_FLAGS=""
+          if [ "${{ inputs.webgpu }}" = "true" ]; then
+            EXTRA_FLAGS="--webgpu"
+          fi
+          scripts/build_macos.sh filament ${{ env.FILAMENT_VERSION }} output --clean $EXTRA_FLAGS
 
       - name: Upload release artifact
         uses: actions/upload-artifact@v4
         with:
-          name: filament-macos-release
-          path: output/filament-${{ env.FILAMENT_VERSION }}-macos-release.zip
+          name: filament-macos-release${{ env.ZIP_SUFFIX }}
+          path: output/filament-${{ env.FILAMENT_VERSION }}-macos-release${{ env.ZIP_SUFFIX }}.zip
           retention-days: 7
 
       - name: Upload debug artifact
         uses: actions/upload-artifact@v4
         with:
-          name: filament-macos-debug
-          path: output/filament-${{ env.FILAMENT_VERSION }}-macos-debug.zip
+          name: filament-macos-debug${{ env.ZIP_SUFFIX }}
+          path: output/filament-${{ env.FILAMENT_VERSION }}-macos-debug${{ env.ZIP_SUFFIX }}.zip
           retention-days: 7
 
       - name: Upload to R2
@@ -126,8 +182,8 @@ jobs:
           pip3 install --break-system-packages awscli
           for variant in release debug; do
             aws s3 cp \
-              "output/filament-${{ env.FILAMENT_VERSION }}-macos-${variant}.zip" \
-              "s3://${{ env.R2_BUCKET_NAME }}/filament-${{ env.FILAMENT_VERSION }}-macos-${variant}.zip" \
+              "output/filament-${{ env.FILAMENT_VERSION }}-macos-${variant}${{ env.ZIP_SUFFIX }}.zip" \
+              "s3://${{ env.R2_BUCKET_NAME }}/filament-${{ env.FILAMENT_VERSION }}-macos-${variant}${{ env.ZIP_SUFFIX }}.zip" \
               --endpoint-url "${{ env.R2_ENDPOINT }}"
           done
         env:
@@ -293,35 +349,61 @@ jobs:
       - name: Install dependencies
         run: |
           sudo apt-get update
-          sudo apt-get install -y clang libc++-dev libc++abi-dev ninja-build libx11-dev libxcursor-dev libxrandr-dev libxinerama-dev libxi-dev libgl1-mesa-dev libglu1-mesa-dev libxxf86vm-dev
+          # Base X11 + Mesa for Filament's own OpenGL/Vulkan paths.
+          # The libxcb-* set is for Dawn's X11/XCB backend (DAWN_USE_X11)
+          # — Dawn pulls in dri3, present, randr, sync, shape, xfixes,
+          # shm-fence and friends. Adding them all up front to avoid the
+          # one-at-a-time CI ping-pong.
+          sudo apt-get install -y \
+            clang libc++-dev libc++abi-dev ninja-build \
+            libx11-dev libx11-xcb-dev \
+            libxcursor-dev libxrandr-dev libxinerama-dev libxi-dev \
+            libxxf86vm-dev libgl1-mesa-dev libglu1-mesa-dev \
+            libxcb1-dev libxcb-dri3-dev libxcb-present-dev \
+            libxcb-randr0-dev libxcb-sync-dev libxcb-shape0-dev \
+            libxcb-xfixes0-dev libxcb-image0-dev libxcb-render0-dev \
+            libxcb-keysyms1-dev libxcb-util-dev libxcb-xkb-dev \
+            libxshmfence-dev libxkbcommon-dev libxkbcommon-x11-dev
+
+      - name: Compute zip suffix
+        run: |
+          if [ "${{ inputs.webgpu }}" = "true" ]; then
+            echo "ZIP_SUFFIX=-webgpu" >> $GITHUB_ENV
+          else
+            echo "ZIP_SUFFIX=" >> $GITHUB_ENV
+          fi
 
       - name: Build Filament
         run: |
           mkdir -p output
           chmod +x scripts/build_linux.sh
-          scripts/build_linux.sh filament ${{ env.FILAMENT_VERSION }} output --clean
+          EXTRA_FLAGS=""
+          if [ "${{ inputs.webgpu }}" = "true" ]; then
+            EXTRA_FLAGS="--webgpu"
+          fi
+          scripts/build_linux.sh filament ${{ env.FILAMENT_VERSION }} output --clean $EXTRA_FLAGS
 
       - name: Upload release artifact
         uses: actions/upload-artifact@v4
         with:
-          name: filament-linux-release
-          path: output/filament-${{ env.FILAMENT_VERSION }}-linux-release.zip
+          name: filament-linux-release${{ env.ZIP_SUFFIX }}
+          path: output/filament-${{ env.FILAMENT_VERSION }}-linux-release${{ env.ZIP_SUFFIX }}.zip
           retention-days: 7
 
       - name: Upload debug artifact
         uses: actions/upload-artifact@v4
         with:
-          name: filament-linux-debug
-          path: output/filament-${{ env.FILAMENT_VERSION }}-linux-debug.zip
+          name: filament-linux-debug${{ env.ZIP_SUFFIX }}
+          path: output/filament-${{ env.FILAMENT_VERSION }}-linux-debug${{ env.ZIP_SUFFIX }}.zip
           retention-days: 7
 
       - name: Upload to R2
         if: inputs.upload_to_r2
         run: |
           for variant in release debug; do
             aws s3 cp \
-              "output/filament-${{ env.FILAMENT_VERSION }}-linux-${variant}.zip" \
-              "s3://${{ env.R2_BUCKET_NAME }}/filament-${{ env.FILAMENT_VERSION }}-linux-${variant}.zip" \
+              "output/filament-${{ env.FILAMENT_VERSION }}-linux-${variant}${{ env.ZIP_SUFFIX }}.zip" \
+              "s3://${{ env.R2_BUCKET_NAME }}/filament-${{ env.FILAMENT_VERSION }}-linux-${variant}${{ env.ZIP_SUFFIX }}.zip" \
               --endpoint-url "${{ env.R2_ENDPOINT }}"
           done
         env:
@@ -522,4 +604,4 @@ jobs:
         env:
           AWS_ACCESS_KEY_ID: ${{ secrets.R2_ACCESS_KEY_ID }}
           AWS_SECRET_ACCESS_KEY: ${{ secrets.R2_SECRET_ACCESS_KEY }}
-          AWS_DEFAULT_REGION: auto
+          AWS_DEFAULT_REGION: auto

docs/upstream.md

@@ -0,0 +1,47 @@
+# Upstream Issues
+
+## Filament WebGPU Blitter: blending enabled on non-blendable formats
+
+**Repository:** google/filament
+**Status:** Unfiled
+**Date:** 2026-06-07
+
+### Summary
+
+The WebGPU `WebGPUBlitter::createRenderPipeline` creates render pipelines with blending enabled unconditionally. When the destination texture format is non-blendable (e.g. `RGBA32Float`), Dawn rejects the pipeline with:
+
+```
+VALIDATION Blending is enabled but color format (TextureFormat::RGBA32Float) is not blendable.
+ - While validating targets[0] framebuffer output.
+ - While validating fragment state.
+ - While calling [Device "graphics_device"].CreateRenderPipeline([RenderPipelineDescriptor ""blitLow""]).
+```
+
+This invalidates the command buffer, causing any subsequent operations in the same encoder (including `CopyTextureToBuffer` for `readPixels`) to be silently discarded.
+
+### Affected Code
+
+- `filament/backend/src/webgpu/WebGPUBlitter.cpp` — `createRenderPipeline()` constructs `wgpu::ColorTargetState` without disabling blending for non-blendable destination formats.
+
+### Reproduction
+
+1. Create a headless WebGPU swapchain (format: `RGBA8Unorm`).
+2. Request `readPixels` with `PixelDataType::FLOAT` (maps to `RGBA32Float`).
+3. `conversionNecessary()` detects format mismatch (`RGBA8Unorm` != `RGBA32Float`).
+4. Blitter creates an intermediate `RGBA32Float` staging texture and attempts to create a render pipeline with blending enabled against it.
+5. Dawn validation rejects the pipeline → command encoder becomes invalid → staging buffer stays empty → pixel buffer is all zeros.
+
+Also reproducible when reading from an `RGBA32Float` render target (e.g. a user-created `TextureFormat.RGBA32F` used as a color attachment), since the blit destination inherits the non-blendable format.
+
+### Suggested Fix
+
+In `WebGPUBlitter::createRenderPipeline()`, check whether the destination format supports blending using `wgpu::TextureFormat::supportsBlend()` (or check `wgpu::TextureFormat` capabilities). When the format is not blendable, set `colorTargetState.blend = nullptr` (no blending) instead of the default blended state.
+
+Alternatively, the readback path in `readTextureToBuffer` could avoid the blit entirely when the only difference is the channel type (e.g., normalized vs. float) by using `CopyTextureToBuffer` directly and handling the type conversion on the CPU side.
+
+### Workaround
+
+Match the pixel data format/type to the source texture format to avoid triggering the conversion blit:
+- For headless swapchains (RGBA8Unorm): use `PixelDataFormat::RGBA` + `PixelDataType::UBYTE`.
+- Avoid `PixelDataType::FLOAT` when reading from non-float textures.
+- Avoid RGBA32Float render targets when readback is needed.

examples/dart/js_wasm/web/example.dart

@@ -1,5 +1,6 @@
 import 'dart:async';
 import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
 import 'dart:math';
 import 'package:web/web.dart';
 import 'package:logging/logging.dart';
@@ -9,6 +10,25 @@ import 'package:thermion_dart/src/filament/src/implementation/ffi_filament_app.d
 import 'web_input_handler.dart';
 import 'package:thermion_dart/src/bindings/src/thermion_dart_js_interop.g.dart';
 
+bool _webGpuAvailable() {
+  final nav = globalContext.getProperty('navigator'.toJS);
+  if (nav == null) return false;
+  return (nav as JSObject).getProperty('gpu'.toJS) != null;
+}
+
+Backend _resolveBackend() {
+  final query = Uri.parse(window.location.href).queryParameters['backend'];
+  if (query == 'webgpu') {
+    if (!_webGpuAvailable()) {
+      print('?backend=webgpu requested but navigator.gpu unavailable; '
+          'falling back to OPENGL.');
+      return Backend.OPENGL;
+    }
+    return Backend.WEBGPU;
+  }
+  return Backend.OPENGL;
+}
+
 void main(List<String> arguments) async {
   Logger.root.onRecord.listen((record) {
     print(record);
@@ -25,7 +45,9 @@ void main(List<String> arguments) async {
     print(err.toString());
   }
 
-  final config = FFIFilamentConfig(backend: Backend.OPENGL);
+  final backend = _resolveBackend();
+  print('Using backend: $backend');
+  final config = FFIFilamentConfig(backend: backend);
 
   await FFIFilamentApp.create(config: config);
 

examples/flutter/quickstart/lib/main.dart

@@ -107,6 +107,14 @@ class _MyHomePageState extends State<MyHomePage> {
   void initState() {
     super.initState();
     _sun = DirectLight.sun(direction: Vector3(0.7, -1, -0.8).normalized());
+    if (kIsWeb) {
+      final wantsWebGpu = Uri.base.queryParameters['backend'] == 'webgpu';
+      final backend = wantsWebGpu && WebGpu.isSupported()
+          ? Backend.WEBGPU
+          : Backend.OPENGL;
+      ThermionFlutterPlugin.instance.setOptions(ThermionFlutterOptions(
+          webOptions: WebOptions(backend: backend)));
+    }
   }
 
   /// Applies the batch: mounts `_batch` viewers at once when the grid is