Ladybird+LibWeb+WebContent: Always use Skia CPU backend in tests mode

Enforce the use of the CPU backend in test mode to ensure that ref-tests
produce consistent results across different computers, as this
consistency cannot be achieved with the GPU backend.

Ladybird/WebContent/main.cpp

@@ -135,7 +135,8 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     Web::set_chrome_process_executable_path(executable_path);
 
     if (use_skia_painter) {
-        WebContent::PageClient::set_use_skia_painter();
+        // Always use the CPU backend for layout tests, as the GPU backend is not deterministic
+        WebContent::PageClient::set_use_skia_painter(is_layout_test_mode ? WebContent::PageClient::UseSkiaPainter::CPUBackend : WebContent::PageClient::UseSkiaPainter::GPUBackendIfAvailable);
     }
 
     if (enable_http_cache) {

Userland/Libraries/LibWeb/HTML/TraversableNavigable.cpp

@@ -30,7 +30,7 @@ TraversableNavigable::TraversableNavigable(JS::NonnullGCPtr<Page> page)
 {
 #ifdef AK_OS_MACOS
     auto display_list_player_type = page->client().display_list_player_type();
-    if (display_list_player_type == DisplayListPlayerType::Skia) {
+    if (display_list_player_type == DisplayListPlayerType::SkiaGPUIfAvailable) {
         m_metal_context = Core::get_metal_context();
         m_skia_backend_context = Painting::DisplayListPlayerSkia::create_metal_context(*m_metal_context);
     }
@@ -38,7 +38,7 @@ TraversableNavigable::TraversableNavigable(JS::NonnullGCPtr<Page> page)
 
 #ifdef USE_VULKAN
     auto display_list_player_type = page->client().display_list_player_type();
-    if (display_list_player_type == DisplayListPlayerType::Skia) {
+    if (display_list_player_type == DisplayListPlayerType::SkiaGPUIfAvailable) {
         auto maybe_vulkan_context = Core::create_vulkan_context();
         if (!maybe_vulkan_context.is_error()) {
             auto vulkan_context = maybe_vulkan_context.release_value();
@@ -1203,8 +1203,8 @@ void TraversableNavigable::paint(DevicePixelRect const& content_rect, Painting::
     paint_config.has_focus = paint_options.has_focus;
     record_display_list(display_list_recorder, paint_config);
 
-    auto display_list_player_type = page().client().display_list_player_type();
+    switch (page().client().display_list_player_type()) {
-    if (display_list_player_type == DisplayListPlayerType::Skia) {
+    case DisplayListPlayerType::SkiaGPUIfAvailable: {
 #ifdef AK_OS_MACOS
         if (m_metal_context && m_skia_backend_context && is<Painting::IOSurfaceBackingStore>(target)) {
             auto& iosurface_backing_store = static_cast<Painting::IOSurfaceBackingStore&>(target);
@@ -1223,11 +1223,23 @@ void TraversableNavigable::paint(DevicePixelRect const& content_rect, Painting::
         }
 #endif
 
+        // Fallback to CPU backend if GPU is not available
         Painting::DisplayListPlayerSkia player(target.bitmap());
         display_list.execute(player);
-    } else {
+        break;
+    }
+    case DisplayListPlayerType::SkiaCPU: {
+        Painting::DisplayListPlayerSkia player(target.bitmap());
+        display_list.execute(player);
+        break;
+    }
+    case DisplayListPlayerType::CPU: {
         Painting::DisplayListPlayerCPU player(target.bitmap());
         display_list.execute(player);
+        break;
+    }
+    default:
+        VERIFY_NOT_REACHED();
     }
 }
 

Userland/Libraries/LibWeb/Page/Page.h

@@ -278,7 +278,8 @@ struct PaintOptions {
 
 enum class DisplayListPlayerType {
     CPU,
-    Skia
+    SkiaGPUIfAvailable,
+    SkiaCPU,
 };
 
 class PageClient : public JS::Cell {

Userland/Libraries/LibWeb/SVG/SVGDecodedImageData.cpp

@@ -105,7 +105,8 @@ RefPtr<Gfx::Bitmap> SVGDecodedImageData::render(Gfx::IntSize size) const
         display_list.execute(executor);
         break;
     }
-    case DisplayListPlayerType::Skia: {
+    case DisplayListPlayerType::SkiaGPUIfAvailable:
+    case DisplayListPlayerType::SkiaCPU: {
         Painting::DisplayListPlayerSkia executor { *bitmap };
         display_list.execute(executor);
         break;

Userland/Services/WebContent/PageClient.cpp

@@ -27,13 +27,13 @@
 
 namespace WebContent {
 
-static bool s_use_skia_painter = false;
+static PageClient::UseSkiaPainter s_use_skia_painter = PageClient::UseSkiaPainter::No;
 
 JS_DEFINE_ALLOCATOR(PageClient);
 
-void PageClient::set_use_skia_painter()
+void PageClient::set_use_skia_painter(UseSkiaPainter use_skia_painter)
 {
-    s_use_skia_painter = true;
+    s_use_skia_painter = use_skia_painter;
 }
 
 JS::NonnullGCPtr<PageClient> PageClient::create(JS::VM& vm, PageHost& page_host, u64 id)
@@ -732,9 +732,16 @@ void PageClient::did_get_js_console_messages(i32 start_index, Vector<ByteString>
 
 Web::DisplayListPlayerType PageClient::display_list_player_type() const
 {
-    if (s_use_skia_painter)
+    switch (s_use_skia_painter) {
-        return Web::DisplayListPlayerType::Skia;
+    case UseSkiaPainter::No:
-    return Web::DisplayListPlayerType::CPU;
+        return Web::DisplayListPlayerType::CPU;
+    case UseSkiaPainter::GPUBackendIfAvailable:
+        return Web::DisplayListPlayerType::SkiaGPUIfAvailable;
+    case UseSkiaPainter::CPUBackend:
+        return Web::DisplayListPlayerType::SkiaCPU;
+    default:
+        VERIFY_NOT_REACHED();
+    }
 }
 
 void PageClient::queue_screenshot_task(Optional<i32> node_id)

Userland/Services/WebContent/PageClient.h

@@ -27,7 +27,12 @@ public:
 
     virtual ~PageClient() override;
 
-    static void set_use_skia_painter();
+    enum class UseSkiaPainter {
+        No,
+        CPUBackend,
+        GPUBackendIfAvailable,
+    };
+    static void set_use_skia_painter(UseSkiaPainter);
 
     virtual void schedule_repaint() override;
     virtual bool is_ready_to_paint() const override;