Add Skia WebAssembly WebGL build

Build a wasm32 static Skia library with Emscripten and WebGL enabled.
Publish and fetch the wasm artifact, and resolve it through the CMake modules
without requiring native zlib or libpng prebuilts.

Author: flsobral

.github/workflows/build-skia.yml

@@ -24,6 +24,7 @@ on:
 
 env:
   ANDROID_NDK_VERSION: 28.2.13676358
+  EMSCRIPTEN_VERSION: 2.0.6
   FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: true
   GITHUB_TOKEN: ${{ github.token }}
   SKIA_DIAGNOSTICS_ARCHIVE: skia-build-diagnostics-158dc9d7.tar.gz
@@ -338,6 +339,83 @@ jobs:
           name: skia-diagnostics-android-arm64-v8a
           path: skia/dist/diagnostics
 
+  build-wasm:
+    name: Build wasm/wasm32
+    needs: prepare-skia-sources
+    runs-on: ubuntu-24.04
+
+    steps:
+      - name: Checkout source code
+        uses: actions/checkout@v6
+
+      - name: Restore ccache
+        uses: actions/cache@v5
+        with:
+          path: .cache/ccache/skia-wasm-wasm32
+          key: skia-ccache-${{ runner.os }}-wasm-wasm32-${{ hashFiles('skia/manifest.json', 'skia/scripts/**') }}
+          restore-keys: |
+            skia-ccache-${{ runner.os }}-wasm-wasm32-
+
+      - name: Install build tools
+        run: sudo apt-get update && sudo apt-get install -y ccache ninja-build rsync
+
+      - name: Setup Emscripten
+        uses: mymindstorm/setup-emsdk@v14
+        with:
+          version: ${{ env.EMSCRIPTEN_VERSION }}
+
+      - name: Restore Skia source archive
+        uses: actions/cache@v5
+        with:
+          path: skia/.source-cache
+          key: ${{ needs.prepare-skia-sources.outputs.cache-key }}
+          enableCrossOsArchive: true
+
+      - name: Extract Skia source archive
+        run: |
+          test -f skia/.source-cache/skia-source.tar
+          tar -C skia -xf skia/.source-cache/skia-source.tar
+
+      - name: Fetch native depot_tools
+        working-directory: skia
+        run: ./scripts/fetch-source.sh depot_tools
+
+      - name: Build static library
+        working-directory: skia
+        env:
+          CCACHE_DIR: ${{ github.workspace }}/.cache/ccache/skia-wasm-wasm32
+          SKIA_SKIP_DEPS_SYNC: 1
+        run: ./scripts/build-wasm32.sh
+
+      - name: Print build summary on failure
+        if: failure()
+        run: |
+          find skia/dist/diagnostics -type f -name 'build-summary.json' -print -exec cat {} \; || true
+
+      - name: Verify artifacts
+        run: |
+          test -f skia/dist/libskia-wasm32.a
+          test -f skia/dist/build_config_manifest-wasm-wasm32.md
+          grep -Eq 'target_cpu[[:space:]]*=[[:space:]]*"wasm"' skia/dist/build_config_manifest-wasm-wasm32.md
+          grep -Eq 'skia_use_webgl[[:space:]]*=[[:space:]]*true' skia/dist/build_config_manifest-wasm-wasm32.md
+          grep -Eq 'skia_gl_standard[[:space:]]*=[[:space:]]*"webgl"' skia/dist/build_config_manifest-wasm-wasm32.md
+          ! find skia/dist -maxdepth 1 -name '*.so' | grep -q .
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v7
+        with:
+          name: skia-wasm-wasm32
+          path: |
+            skia/dist/libskia-wasm32.a
+            skia/dist/build_config_manifest-wasm-wasm32.md
+
+      - name: Upload diagnostics
+        if: always()
+        uses: actions/upload-artifact@v7
+        with:
+          name: skia-diagnostics-wasm-wasm32
+          path: skia/dist/diagnostics
+
   build-apple:
     name: Build ${{ matrix.platform_arch }}
     runs-on: macos-15
@@ -581,6 +659,7 @@ jobs:
     needs:
       - build-linux
       - build-android
+      - build-wasm
       - build-apple
       - package-ios
       - build-windows

.github/workflows/release-skia.yml

@@ -122,4 +122,4 @@ jobs:
           gh release create "${TAG_NAME}" "${release_files[@]}" \
             --verify-tag \
             --title "Skia ${SKIA_VERSION} static libraries" \
-            --notes "Static Skia ${SKIA_VERSION} libraries for TotalCross, including Android arm64-v8a with NDK ${ANDROID_NDK_VERSION:-28.2.13676358}, iOS device/simulator arm64 artifacts, and a separate diagnostics archive with full GN/Ninja logs."
+            --notes "Static Skia ${SKIA_VERSION} libraries for TotalCross, including WebAssembly/WebGL wasm32, Android arm64-v8a with NDK ${ANDROID_NDK_VERSION:-28.2.13676358}, iOS device/simulator arm64 artifacts, and a separate diagnostics archive with full GN/Ninja logs."

skia/README.md

@@ -10,6 +10,7 @@ describes the GitHub Release assets consumed by TotalCross.
 
 ```bash
 ./fetch.sh --platform linux --arch x86_64 --install-dev
+./fetch.sh --platform wasm --arch wasm32 --install-dev
 ./fetch.sh --platform macos --arch arm64 --install-dev
 ./fetch.sh --platform android --arch arm64-v8a
 ./fetch.sh --platform ios --arch arm64 --install-dev
@@ -27,6 +28,7 @@ in `artifacts.json`. Override it with `--base-url`, `--github-repo`,
 ./scripts/build-linux-x86_64.sh
 ./scripts/build-linux-aarch64.sh
 ./scripts/build-linux-armv7l.sh
+./scripts/build-wasm32.sh
 ./scripts/build-android-arm64.sh
 ./scripts/build-ios-arm64.sh
 ./scripts/build-ios-simulator-arm64.sh

skia/artifacts.json

@@ -17,6 +17,7 @@
             "libskia-linux-x86_64.a",
             "libskia-linux-aarch64.a",
             "libskia-linux-armv7l.a",
+            "libskia-wasm32.a",
             "libskia-android-arm64-v8a.a",
             "libskia-macos-arm64.a",
             "libskia-ios-arm64.a",
@@ -28,6 +29,7 @@
             "build_config_manifest-linux-x86_64.md",
             "build_config_manifest-linux-aarch64.md",
             "build_config_manifest-linux-armv7l.md",
+            "build_config_manifest-wasm-wasm32.md",
             "build_config_manifest-android-arm64-v8a.md",
             "build_config_manifest-macos-arm64.md",
             "build_config_manifest-ios-arm64.md",
@@ -63,6 +65,10 @@
             "artifact_name": "libskia-linux-armv7l.a",
             "target_path": "local/out/Release/linux/armv7l/libskia.a"
         },
+        "wasm-wasm32": {
+            "artifact_name": "libskia-wasm32.a",
+            "target_path": "local/out/Release/wasm/wasm32/libskia.a"
+        },
         "android-arm64-v8a": {
             "artifact_name": "libskia-android-arm64-v8a.a",
             "target_path": "local/out/Release/android/arm64-v8a/libskia.a"
@@ -106,6 +112,10 @@
                 "artifact_name": "build_config_manifest-linux-armv7l.md",
                 "target_path": "local/out/Release/linux/armv7l/build_config_manifest.md"
             },
+            "wasm-wasm32": {
+                "artifact_name": "build_config_manifest-wasm-wasm32.md",
+                "target_path": "local/out/Release/wasm/wasm32/build_config_manifest.md"
+            },
             "android-arm64-v8a": {
                 "artifact_name": "build_config_manifest-android-arm64-v8a.md",
                 "target_path": "local/out/Release/android/arm64-v8a/build_config_manifest.md"

skia/cmake/AutoFetchSkia.cmake

@@ -92,8 +92,6 @@ function(tcvm_auto_fetch_skia)
     return()
   endif()
 
-  tcvm_auto_fetch_skia_dependencies()
-
   find_program(TCVM_BASH_EXECUTABLE bash)
   if(NOT TCVM_BASH_EXECUTABLE)
     message(FATAL_ERROR "Unable to auto-fetch Skia because 'bash' was not found")
@@ -156,6 +154,11 @@ function(tcvm_auto_fetch_skia)
 
     set(TCVM_FETCH_INSTALL_DEV ON)
     set(TCVM_SKIA_ARTIFACT "${TCVM_SKIA_DIR}/out/Release/macos/${TCVM_FETCH_ARCH}/libskia.a")
+  elseif(CMAKE_SYSTEM_NAME STREQUAL "Emscripten")
+    set(TCVM_FETCH_PLATFORM "wasm")
+    set(TCVM_FETCH_ARCH "wasm32")
+    set(TCVM_FETCH_INSTALL_DEV ON)
+    set(TCVM_SKIA_ARTIFACT "${TCVM_SKIA_DIR}/out/Release/wasm/wasm32/libskia.a")
   elseif(UNIX AND (CMAKE_SYSTEM_NAME STREQUAL "Linux"))
     set(TCVM_FETCH_PLATFORM "linux")
     set(TCVM_FETCH_ARCH "${CMAKE_SYSTEM_PROCESSOR}")
@@ -193,6 +196,10 @@ function(tcvm_auto_fetch_skia)
     return()
   endif()
 
+  if(NOT TCVM_FETCH_PLATFORM STREQUAL "wasm")
+    tcvm_auto_fetch_skia_dependencies()
+  endif()
+
   if(TCVM_FETCH_INSTALL_DEV)
     if(NOT EXISTS "${TCVM_SKIA_DIR}/include/core/SkCanvas.h" OR NOT EXISTS "${TCVM_SKIA_DIR}/src/gpu/gl/GrGLDefines.h")
       set(TCVM_FETCH_NEEDED ON)

skia/cmake/FindSkia.cmake

@@ -69,6 +69,9 @@ elseif(APPLE)
   elseif(SKIA_ARCH STREQUAL "aarch64")
     set(SKIA_ARCH "arm64")
   endif()
+elseif(CMAKE_SYSTEM_NAME STREQUAL "Emscripten")
+  set(SKIA_PLATFORM "wasm")
+  set(SKIA_ARCH "wasm32")
 elseif(UNIX AND CMAKE_SYSTEM_NAME STREQUAL "Linux")
   set(SKIA_PLATFORM "linux")
   set(SKIA_ARCH "${CMAKE_SYSTEM_PROCESSOR}")
@@ -203,13 +206,17 @@ find_package_handle_standard_args(Skia
 )
 
 if(Skia_FOUND AND NOT TARGET Skia::Skia)
-  find_package(ZLIB REQUIRED MODULE)
-  find_package(PNG REQUIRED MODULE)
+  set(SKIA_INTERFACE_LIBRARIES "")
+  if(NOT SKIA_PLATFORM STREQUAL "wasm")
+    find_package(ZLIB REQUIRED MODULE)
+    find_package(PNG REQUIRED MODULE)
+    set(SKIA_INTERFACE_LIBRARIES "PNG::PNG;ZLIB::ZLIB")
+  endif()
 
   add_library(Skia::Skia UNKNOWN IMPORTED)
   set_target_properties(Skia::Skia PROPERTIES
     IMPORTED_LOCATION "${SKIA_LIBRARY}"
     INTERFACE_INCLUDE_DIRECTORIES "${SKIA_INCLUDE_DIRS}"
-    INTERFACE_LINK_LIBRARIES "PNG::PNG;ZLIB::ZLIB"
+    INTERFACE_LINK_LIBRARIES "${SKIA_INTERFACE_LIBRARIES}"
   )
 endif()

skia/fetch.sh

@@ -22,9 +22,9 @@ an artifact base URL or a GitHub Release.
 
 Options:
   --platform <name>   Target platform: ios, ios-simulator, macos, linux,
-                      android, windows.
+                      wasm, android, windows.
   --arch <name>       Target arch/ABI: arm64, x86, x64, x86_64, aarch64,
-                      armv7l, arm64-v8a.
+                      armv7l, wasm32, arm64-v8a.
   --source <path|url> Install from a specific local file or URL.
   --base-url <url>    Base URL used with the manifest artifact_name.
   --github-repo <r>   GitHub repo in owner/name format.
@@ -194,6 +194,7 @@ normalize_platform() {
     ios-simulator|iphonesimulator) echo "ios-simulator" ;;
     Darwin|darwin|macos|mac|osx) echo "macos" ;;
     Linux|linux) echo "linux" ;;
+    wasm|wasm32|Emscripten|emscripten) echo "wasm" ;;
     Android|android) echo "android" ;;
     Windows|windows|mingw*|MINGW*|msys*|MSYS*) echo "windows" ;;
     *) die "unsupported platform: $1" ;;
@@ -208,6 +209,7 @@ normalize_arch() {
     x64) echo "x64" ;;
     x86|i386|i686) echo "x86" ;;
     armv7l|armv7) echo "armv7l" ;;
+    wasm|wasm32) echo "wasm32" ;;
     arm64-v8a) echo "arm64-v8a" ;;
     *) die "unsupported architecture/ABI: $1" ;;
   esac

skia/manifest.json

@@ -17,6 +17,7 @@
             "libskia-linux-x86_64.a",
             "libskia-linux-aarch64.a",
             "libskia-linux-armv7l.a",
+            "libskia-wasm32.a",
             "libskia-android-arm64-v8a.a",
             "libskia-macos-arm64.a",
             "libskia-ios-arm64.a",
@@ -28,6 +29,7 @@
             "build_config_manifest-linux-x86_64.md",
             "build_config_manifest-linux-aarch64.md",
             "build_config_manifest-linux-armv7l.md",
+            "build_config_manifest-wasm-wasm32.md",
             "build_config_manifest-android-arm64-v8a.md",
             "build_config_manifest-macos-arm64.md",
             "build_config_manifest-ios-arm64.md",

skia/manifest.yml

@@ -18,6 +18,7 @@ artifact:
     - libskia-linux-x86_64.a
     - libskia-linux-aarch64.a
     - libskia-linux-armv7l.a
+    - libskia-wasm32.a
     - libskia-android-arm64-v8a.a
     - libskia-macos-arm64.a
     - libskia-ios-arm64.a

skia/scripts/build-wasm32.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+SCRIPT_DIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+source "$SCRIPT_DIR/common.sh"
+
+build_skia_wasm32