Shadows paint at the wrong scale in replayed CGDisplayLists

https://bugs.webkit.org/show_bug.cgi?id=246369 rdar://96967173 Reviewed by Simon Fraser. * Source/WebCore/platform/graphics/cg/GraphicsContextCG.cpp: (WebCore::GraphicsContextCG::fillRect): (WebCore::GraphicsContextCG::fillRoundedRectImpl): (WebCore::GraphicsContextCG::fillRectWithRoundedHole): (WebCore::GraphicsContextCG::setCGShadow): (WebCore::GraphicsContextCG::clearCGShadow): (WebCore::GraphicsContextCG::didUpdateState): (WebCore::setCGShadow): Deleted. Make setCGShadow virtual so that GraphicsContextCGDisplayList can adjust its behavior. Drive-by factor out clearCGShadow so all the CGContext-touching code is all in one place. * Source/WebCore/platform/graphics/cg/GraphicsContextCG.h: * Source/WebKit/Shared/RemoteLayerTree/CGDisplayListImageBufferBackend.mm: (WebKit::GraphicsContextCGDisplayList::GraphicsContextCGDisplayList): Work around a confusion re: the base CTM with CGDisplayList image buffers by mapping the shadow parameters out through the hidden immutable base transform. We don't actually use the transform here, instead just faking it with the scale and flip, because we have no mechanism for mapping a size with negative values through an AffineTransform. Canonical link: https://commits.webkit.org/255442@main
WebKit · Oct 12, 2022 · ff0ba2b · ff0ba2b
1 parent eeb0925
commit ff0ba2b
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Showing 3 changed files with 29 additions and 11 deletions.
diff --git a/Source/WebCore/platform/graphics/cg/GraphicsContextCG.cpp b/Source/WebCore/platform/graphics/cg/GraphicsContextCG.cpp
@@ -816,8 +816,7 @@ void GraphicsContextCG::fillRect(const FloatRect& rect)
     bool drawOwnShadow = canUseShadowBlur();
     CGContextStateSaver stateSaver(context, drawOwnShadow);
     if (drawOwnShadow) {
-        // Turn off CG shadows.
-        CGContextSetShadowWithColor(platformContext(), CGSizeZero, 0, 0);
+        clearCGShadow();
 
         ShadowBlur contextShadow(dropShadow(), shadowsIgnoreTransforms());
         contextShadow.drawRectShadow(*this, FloatRoundedRect(rect));
@@ -837,8 +836,7 @@ void GraphicsContextCG::fillRect(const FloatRect& rect, const Color& color)
     bool drawOwnShadow = canUseShadowBlur();
     CGContextStateSaver stateSaver(context, drawOwnShadow);
     if (drawOwnShadow) {
-        // Turn off CG shadows.
-        CGContextSetShadowWithColor(platformContext(), CGSizeZero, 0, 0);
+        clearCGShadow();
 
         ShadowBlur contextShadow(dropShadow(), shadowsIgnoreTransforms());
         contextShadow.drawRectShadow(*this, FloatRoundedRect(rect));
@@ -864,8 +862,7 @@ void GraphicsContextCG::fillRoundedRectImpl(const FloatRoundedRect& rect, const
     bool drawOwnShadow = canUseShadowBlur();
     CGContextStateSaver stateSaver(context, drawOwnShadow);
     if (drawOwnShadow) {
-        // Turn off CG shadows.
-        CGContextSetShadowWithColor(platformContext(), CGSizeZero, 0, 0);
+        clearCGShadow();
 
         ShadowBlur contextShadow(dropShadow(), shadowsIgnoreTransforms());
         contextShadow.drawRectShadow(*this, rect);
@@ -913,8 +910,7 @@ void GraphicsContextCG::fillRectWithRoundedHole(const FloatRect& rect, const Flo
     bool drawOwnShadow = canUseShadowBlur();
     CGContextStateSaver stateSaver(context, drawOwnShadow);
     if (drawOwnShadow) {
-        // Turn off CG shadows.
-        CGContextSetShadowWithColor(platformContext(), CGSizeZero, 0, 0);
+        clearCGShadow();
 
         ShadowBlur contextShadow(dropShadow(), shadowsIgnoreTransforms());
         contextShadow.drawInsetShadow(*this, rect, roundedHoleRect);
@@ -1030,10 +1026,10 @@ static void applyShadowOffsetWorkaroundIfNeeded(CGContextRef context, CGFloat& x
 #endif
 }
 
-static void setCGShadow(CGContextRef context, RenderingMode renderingMode, const FloatSize& offset, float blur, const Color& color, bool shadowsIgnoreTransforms)
+void GraphicsContextCG::setCGShadow(RenderingMode renderingMode, const FloatSize& offset, float blur, const Color& color, bool shadowsIgnoreTransforms)
 {
     if (offset.isZero() && !blur) {
-        CGContextSetShadowWithColor(context, CGSizeZero, 0, 0);
+        clearCGShadow();
         return;
     }
 
@@ -1042,6 +1038,7 @@ static void setCGShadow(CGContextRef context, RenderingMode renderingMode, const
     CGFloat xOffset = offset.width();
     CGFloat yOffset = offset.height();
     CGFloat blurRadius = blur;
+    CGContextRef context = platformContext();
 
     if (!shadowsIgnoreTransforms) {
         CGAffineTransform userToBaseCTM = getUserToBaseCTM(context);
@@ -1075,6 +1072,11 @@ static void setCGShadow(CGContextRef context, RenderingMode renderingMode, const
         CGContextSetShadowWithColor(context, CGSizeMake(xOffset, yOffset), blurRadius, cachedCGColor(color).get());
 }
 
+void GraphicsContextCG::clearCGShadow()
+{
+    CGContextSetShadowWithColor(platformContext(), CGSizeZero, 0, 0);
+}
+
 void GraphicsContextCG::didUpdateState(GraphicsContextState& state)
 {
     if (!state.changes())
@@ -1101,7 +1103,7 @@ void GraphicsContextCG::didUpdateState(GraphicsContextState& state)
             break;
 
         case GraphicsContextState::Change::DropShadow:
-            setCGShadow(context, renderingMode(), state.dropShadow().offset, state.dropShadow().blurRadius, state.dropShadow().color, state.shadowsIgnoreTransforms());
+            setCGShadow(renderingMode(), state.dropShadow().offset, state.dropShadow().blurRadius, state.dropShadow().color, state.shadowsIgnoreTransforms());
             break;
 
         case GraphicsContextState::Change::Alpha:

diff --git a/Source/WebCore/platform/graphics/cg/GraphicsContextCG.h b/Source/WebCore/platform/graphics/cg/GraphicsContextCG.h
@@ -135,9 +135,14 @@ class WEBCORE_EXPORT GraphicsContextCG : public GraphicsContext {
     GraphicsContextPlatformPrivate* deprecatedPrivateContext() const final;
 #endif
 
+protected:
+    virtual void setCGShadow(RenderingMode, const FloatSize& offset, float blur, const Color&, bool shadowsIgnoreTransforms);
+
 private:
     void convertToDestinationColorSpaceIfNeeded(RetainPtr<CGImageRef>&);
 
+    void clearCGShadow();
+
     GraphicsContextPlatformPrivate* m_data { nullptr };
 };
 

diff --git a/Source/WebKit/Shared/RemoteLayerTree/CGDisplayListImageBufferBackend.mm b/Source/WebKit/Shared/RemoteLayerTree/CGDisplayListImageBufferBackend.mm
@@ -54,6 +54,7 @@
         m_immutableBaseTransform.translate(0, -ceilf(parameters.logicalSize.height() * parameters.resolutionScale));
         m_immutableBaseTransform.scale(parameters.resolutionScale);
         m_inverseImmutableBaseTransform = *m_immutableBaseTransform.inverse();
+        m_resolutionScale = parameters.resolutionScale;
     }
 
     void setCTM(const WebCore::AffineTransform& transform) final
@@ -68,9 +69,19 @@ void setCTM(const WebCore::AffineTransform& transform) final
 
     bool canUseShadowBlur() const final { return false; }
 
+protected:
+    void setCGShadow(WebCore::RenderingMode renderingMode, const WebCore::FloatSize& offset, float blur, const WebCore::Color& color, bool shadowsIgnoreTransforms) override
+    {
+        // This doesn't use `m_immutableBaseTransform.mapSize` because it doesn't output negative lengths.
+        WebCore::FloatSize scaledOffset = offset;
+        scaledOffset.scale(m_resolutionScale, -m_resolutionScale);
+        GraphicsContextCG::setCGShadow(renderingMode, scaledOffset, blur * m_resolutionScale, color, shadowsIgnoreTransforms);
+    }
+
 private:
     WebCore::AffineTransform m_immutableBaseTransform;
     WebCore::AffineTransform m_inverseImmutableBaseTransform;
+    float m_resolutionScale;
 };
 
 WTF_MAKE_ISO_ALLOCATED_IMPL(CGDisplayListImageBufferBackend);