Transparent, composited canvas is rendered black when layer is change…

…d to render layer backing sharing

https://bugs.webkit.org/show_bug.cgi?id=258927
rdar://110088034

Reviewed by Simon Fraser.

Explicitly composited canvas element might switch to being
composited to other RenderLayerBacking. This left the
RenderLayer::m_shouldPaintUsingCompositeCopy unreset.

Instead, store the flag to RenderLayerBacking.

* Source/WebCore/html/HTMLCanvasElement.cpp:
(WebCore::HTMLCanvasElement::paint):
* Source/WebCore/html/HTMLCanvasElement.h:
* Source/WebCore/rendering/RenderHTMLCanvas.cpp:
(WebCore::RenderHTMLCanvas::paintReplaced):
* Source/WebCore/rendering/RenderLayer.cpp:
(WebCore::RenderLayer::RenderLayer):
* Source/WebCore/rendering/RenderLayer.h:
(WebCore::RenderLayer::shouldPaintUsingCompositeCopy const): Deleted.
(WebCore::RenderLayer::setShouldPaintUsingCompositeCopy): Deleted.
* Source/WebCore/rendering/RenderLayerBacking.cpp:
(WebCore::RenderLayerBacking::updateConfiguration):
(WebCore::RenderLayerBacking::paintIntoLayer):
* Source/WebCore/rendering/RenderLayerBacking.h:

Canonical link: https://commits.webkit.org/265837@main

Source/WebCore/html/HTMLCanvasElement.cpp

@@ -637,7 +637,7 @@ bool HTMLCanvasElement::paintsIntoCanvasBuffer() const
 
 
 
-void HTMLCanvasElement::paint(GraphicsContext& context, const LayoutRect& r, CompositeOperator op)
+void HTMLCanvasElement::paint(GraphicsContext& context, const LayoutRect& r)
 {
     if (m_context)
         m_context->clearAccumulatedDirtyRect();
@@ -656,7 +656,7 @@ void HTMLCanvasElement::paint(GraphicsContext& context, const LayoutRect& r, Com
         if (shouldPaint) {
             if (hasCreatedImageBuffer()) {
                 if (ImageBuffer* imageBuffer = buffer())
-                    context.drawImageBuffer(*imageBuffer, snappedIntRect(r), op);
+                    context.drawImageBuffer(*imageBuffer, snappedIntRect(r), context.compositeOperation());
             }
         }
     }

Source/WebCore/html/HTMLCanvasElement.h

@@ -108,7 +108,7 @@ class HTMLCanvasElement final : public HTMLElement, public CanvasBase, public Ac
     // Used for rendering
     void didDraw(const std::optional<FloatRect>&, ShouldApplyPostProcessingToDirtyRect) final;
 
-    void paint(GraphicsContext&, const LayoutRect&, CompositeOperator);
+    void paint(GraphicsContext&, const LayoutRect&);
 
 #if ENABLE(MEDIA_STREAM) || ENABLE(WEB_CODECS)
     RefPtr<VideoFrame> toVideoFrame();

Source/WebCore/rendering/RenderHTMLCanvas.cpp

@@ -98,12 +98,7 @@ void RenderHTMLCanvas::paintReplaced(PaintInfo& paintInfo, const LayoutPoint& pa
     InterpolationQualityMaintainer interpolationMaintainer(context, ImageQualityController::interpolationQualityFromStyle(style()));
 
     canvasElement().setIsSnapshotting(paintInfo.paintBehavior.contains(PaintBehavior::Snapshotting));
-    CompositeOperator op = CompositeOperator::SourceOver;
-#if ENABLE(CSS_COMPOSITING)
-    if (paintInfo.enclosingSelfPaintingLayer() && paintInfo.enclosingSelfPaintingLayer()->shouldPaintUsingCompositeCopy())
-        op = CompositeOperator::Copy;
-#endif
-    canvasElement().paint(context, replacedContentRect, op);
+    canvasElement().paint(context, replacedContentRect);
     canvasElement().setIsSnapshotting(false);
 }
 

Source/WebCore/rendering/RenderLayer.cpp

@@ -337,7 +337,6 @@ RenderLayer::RenderLayer(RenderLayerModelObject& renderer)
     , m_hasTransformedAncestor(false)
     , m_has3DTransformedAncestor(false)
     , m_insideSVGForeignObject(false)
-    , m_shouldPaintUsingCompositeCopy(false)
     , m_indirectCompositingReason(static_cast<unsigned>(IndirectCompositingReason::None))
     , m_viewportConstrainedNotCompositedReason(NoNotCompositedReason)
 #if ASSERT_ENABLED

Source/WebCore/rendering/RenderLayer.h

@@ -786,7 +786,6 @@ class RenderLayer : public CanMakeWeakPtr<RenderLayer> {
     bool hasNotIsolatedBlendingDescendantsStatusDirty() const { return false; }
 #endif
 
-    bool shouldPaintUsingCompositeCopy() const { return m_shouldPaintUsingCompositeCopy; }
     bool isComposited() const { return m_backing != nullptr; }
     bool hasCompositingDescendant() const { return m_hasCompositingDescendant; }
     bool hasCompositedMask() const;
@@ -1144,8 +1143,6 @@ class RenderLayer : public CanMakeWeakPtr<RenderLayer> {
 
     bool computeHasVisibleContent() const;
 
-    void setShouldPaintUsingCompositeCopy(bool copy) { m_shouldPaintUsingCompositeCopy = copy; }
-
     bool has3DTransformedDescendant() const { return m_has3DTransformedDescendant; }
     bool has3DTransformedAncestor() const { return m_has3DTransformedAncestor; }
 
@@ -1251,7 +1248,6 @@ class RenderLayer : public CanMakeWeakPtr<RenderLayer> {
     bool m_has3DTransformedAncestor : 1;
 
     bool m_insideSVGForeignObject : 1;
-    bool m_shouldPaintUsingCompositeCopy : 1;
     bool m_isHiddenByOverflowTruncation : 1 { false };
 
     unsigned m_indirectCompositingReason : 4; // IndirectCompositingReason

Source/WebCore/rendering/RenderLayerBacking.cpp

@@ -1135,14 +1135,12 @@ bool RenderLayerBacking::updateConfiguration(const RenderLayer* compositingAnces
         layerConfigChanged = true;
     }
 
-#if ENABLE(CSS_COMPOSITING)
     bool shouldPaintUsingCompositeCopy = unscaledBitmap && is<RenderHTMLCanvas>(renderer());
-    if (shouldPaintUsingCompositeCopy != m_owningLayer.shouldPaintUsingCompositeCopy()) {
-        m_owningLayer.setShouldPaintUsingCompositeCopy(shouldPaintUsingCompositeCopy);
+    if (shouldPaintUsingCompositeCopy != m_shouldPaintUsingCompositeCopy) {
+        m_shouldPaintUsingCompositeCopy = shouldPaintUsingCompositeCopy;
         m_graphicsLayer->setShouldPaintUsingCompositeCopy(shouldPaintUsingCompositeCopy);
         layerConfigChanged = true;
     }
-#endif
 
     if (is<RenderEmbeddedObject>(renderer()) && downcast<RenderEmbeddedObject>(renderer()).allowsAcceleratedCompositing()) {
         auto* pluginViewBase = downcast<PluginViewBase>(downcast<RenderWidget>(renderer()).widget());
@@ -3443,7 +3441,6 @@ void RenderLayerBacking::paintIntoLayer(const GraphicsLayer* graphicsLayer, Grap
 #endif
         return;
     }
-
     auto paintFlags = paintFlagsForLayer(*graphicsLayer);
 
     if (is<EventRegionContext>(regionContext))
@@ -3464,8 +3461,16 @@ void RenderLayerBacking::paintIntoLayer(const GraphicsLayer* graphicsLayer, Grap
         paintingInfo.regionContext = regionContext;
 
         if (&layer == &m_owningLayer) {
-            layer.paintLayerContents(context, paintingInfo, paintFlags);
-
+            {
+                bool shouldResetCompositeMode = false;
+                if (m_shouldPaintUsingCompositeCopy && context.compositeMode() == CompositeMode { CompositeOperator::SourceOver, BlendMode::Normal }) {
+                    context.setCompositeMode({ CompositeOperator::Copy, BlendMode::Normal });
+                    shouldResetCompositeMode = true;
+                }
+                layer.paintLayerContents(context, paintingInfo, paintFlags);
+                if (shouldResetCompositeMode)
+                    context.setCompositeMode({ CompositeOperator::SourceOver, BlendMode::Normal });
+            }
             auto* scrollableArea = layer.scrollableArea();
             if (scrollableArea && scrollableArea->containsDirtyOverlayScrollbars() && !regionContext)
                 layer.paintLayerContents(context, paintingInfo, paintFlags | RenderLayer::PaintLayerFlag::PaintingOverlayScrollbars);

Source/WebCore/rendering/RenderLayerBacking.h

@@ -289,6 +289,7 @@ class RenderLayerBacking final : public GraphicsLayerClient {
     WEBCORE_EXPORT void setIsTrackingDisplayListReplay(bool);
     WEBCORE_EXPORT String replayDisplayListAsText(OptionSet<DisplayList::AsTextFlag>) const;
 
+    bool shouldPaintUsingCompositeCopy() const { return m_shouldPaintUsingCompositeCopy; }
 private:
     friend class PaintedContentsInfo;
 
@@ -456,6 +457,7 @@ class RenderLayerBacking final : public GraphicsLayerClient {
 #if ENABLE(ASYNC_SCROLLING)
     bool m_needsEventRegionUpdate { true };
 #endif
+    bool m_shouldPaintUsingCompositeCopy { false };
 };
 
 enum CanvasCompositingStrategy {

Source/WebKit/WebProcess/GPU/graphics/RemoteImageBufferProxy.h

@@ -94,8 +94,6 @@ class RemoteImageBufferProxy : public WebCore::ImageBuffer {
     void convertToLuminanceMask() final;
     void transformToColorSpace(const WebCore::DestinationColorSpace&) final;
 
-    bool prefersPreparationForDisplay() final { return true; }
-
     void flushDrawingContext() final;
     bool flushDrawingContextAsync() final;