Bug 602757. Part 2: Detect display items over the transparent part of a window, and disable usage of component alpha (i.e., subpixel antialiasing) for those items. r=tnikkel,a=blocking

layout/base/FrameLayerBuilder.cpp

@@ -895,6 +895,29 @@ ContainerState::PopThebesLayerData()
   mThebesLayerDataStack.RemoveElementAt(lastIndex);
 }
 
+static PRBool
+SuppressComponentAlpha(nsDisplayListBuilder* aBuilder,
+                       nsDisplayItem* aItem)
+{
+  const nsRegion* windowTransparentRegion = aBuilder->GetFinalTransparentRegion();
+  if (!windowTransparentRegion || windowTransparentRegion->IsEmpty())
+    return PR_FALSE;
+
+  // Suppress component alpha for items in the toplevel window that are over
+  // the window translucent area
+  nsIFrame* f = aItem->GetUnderlyingFrame();
+  nsIFrame* ref = aBuilder->ReferenceFrame();
+  if (f->PresContext() != ref->PresContext())
+    return PR_FALSE;
+
+  for (nsIFrame* t = f; t; t = t->GetParent()) {
+    if (t->IsTransformed())
+      return PR_FALSE;
+  }
+
+  return windowTransparentRegion->Intersects(aItem->GetBounds(aBuilder));
+}
+
 void
 ContainerState::ThebesLayerData::Accumulate(nsDisplayListBuilder* aBuilder,
                                             nsDisplayItem* aItem,
@@ -937,7 +960,11 @@ ContainerState::ThebesLayerData::Accumulate(nsDisplayListBuilder* aBuilder,
     }
   } else if (aItem->HasText()) {
     if (!mOpaqueRegion.Contains(aVisibleRect)) {
-      mNeedComponentAlpha = PR_TRUE;
+      if (SuppressComponentAlpha(aBuilder, aItem)) {
+        aItem->DisableComponentAlpha();
+      } else {
+        mNeedComponentAlpha = PR_TRUE;
+      }
     }
   }
   mForceTransparentSurface = mForceTransparentSurface || forceTransparentSurface;

layout/base/nsDisplayList.cpp

@@ -73,6 +73,7 @@ nsDisplayListBuilder::nsDisplayListBuilder(nsIFrame* aReferenceFrame,
     : mReferenceFrame(aReferenceFrame),
       mIgnoreScrollFrame(nsnull),
       mCurrentTableItem(nsnull),
+      mFinalTransparentRegion(nsnull),
       mMode(aMode),
       mBuildCaret(aBuildCaret),
       mIgnoreSuppression(PR_FALSE),

layout/base/nsDisplayList.h

@@ -338,6 +338,19 @@ public:
    */
   FrameLayerBuilder* LayerBuilder() { return &mLayerBuilder; }
 
+  /**
+   * Get the area of the final transparent region.
+   */
+  const nsRegion* GetFinalTransparentRegion() { return mFinalTransparentRegion; }
+  /**
+   * Record the area of the final transparent region after all visibility
+   * calculations were performed.
+   */
+  void SetFinalTransparentRegion(const nsRegion& aFinalTransparentRegion)
+  {
+    mFinalTransparentRegion = &aFinalTransparentRegion;
+  }
+
   /**
    * Returns true if we need to descend into this frame when building
    * the display list, even though it doesn't intersect the dirty
@@ -422,6 +435,7 @@ private:
   nsAutoTArray<PresShellState,8> mPresShellStates;
   nsAutoTArray<nsIFrame*,100>    mFramesMarkedForDisplay;
   nsDisplayTableItem*            mCurrentTableItem;
+  const nsRegion*                mFinalTransparentRegion;
   Mode                           mMode;
   PRPackedBool                   mBuildCaret;
   PRPackedBool                   mIgnoreSuppression;
@@ -702,6 +716,11 @@ public:
    */
   virtual PRBool HasText() { return PR_FALSE; }
 
+  /**
+   * Disable usage of component alpha. Currently only relevant for items that have text.
+   */
+  virtual void DisableComponentAlpha() {}
+
 protected:
   friend class nsDisplayList;
   

layout/base/nsLayoutUtils.cpp

@@ -1409,11 +1409,8 @@ nsLayoutUtils::PaintFrame(nsIRenderingContext* aRenderingContext, nsIFrame* aFra
   PRUint32 flags = nsDisplayList::PAINT_DEFAULT;
   if (aFlags & PAINT_WIDGET_LAYERS) {
     flags |= nsDisplayList::PAINT_USE_WIDGET_LAYERS;
-    nsIWidget *widget = aFrame->GetNearestWidget();
-    PRInt32 pixelRatio = presContext->AppUnitsPerDevPixel();
-    nsIntRegion visibleWindowRegion(visibleRegion.ToOutsidePixels(pixelRatio));
-    nsIntRegion dirtyWindowRegion(aDirtyRegion.ToOutsidePixels(pixelRatio));
 
+    nsIWidget *widget = aFrame->GetNearestWidget();
     if (willFlushRetainedLayers) {
       // The caller wanted to paint from retained layers, but set up
       // the paint in such a way that we can't use them.  We're going
@@ -1426,6 +1423,10 @@ nsLayoutUtils::PaintFrame(nsIRenderingContext* aRenderingContext, nsIFrame* aFra
     } else if (widget && !(aFlags & PAINT_DOCUMENT_RELATIVE)) {
       // XXX we should simplify this API now that dirtyWindowRegion always
       // covers the entire window
+      PRInt32 pixelRatio = presContext->AppUnitsPerDevPixel();
+      nsIntRegion visibleWindowRegion(visibleRegion.ToOutsidePixels(pixelRatio));
+      nsIntRegion dirtyWindowRegion(aDirtyRegion.ToOutsidePixels(pixelRatio));
+      builder.SetFinalTransparentRegion(visibleRegion);
       widget->UpdatePossiblyTransparentRegion(dirtyWindowRegion, visibleWindowRegion);
     }
   }

layout/generic/nsTextFrameThebes.cpp

@@ -4039,7 +4039,8 @@ nsTextFrame::DidSetStyleContext(nsStyleContext* aOldStyleContext)
 class nsDisplayText : public nsDisplayItem {
 public:
   nsDisplayText(nsDisplayListBuilder* aBuilder, nsTextFrame* aFrame) :
-    nsDisplayItem(aBuilder, aFrame) {
+    nsDisplayItem(aBuilder, aFrame),
+    mDisableSubpixelAA(PR_FALSE) {
     MOZ_COUNT_CTOR(nsDisplayText);
   }
 #ifdef NS_BUILD_REFCNT_LOGGING
@@ -4062,6 +4063,10 @@ public:
   NS_DISPLAY_DECL_NAME("Text", TYPE_TEXT)
 
   virtual PRBool HasText() { return PR_TRUE; }
+
+  virtual void DisableComponentAlpha() { mDisableSubpixelAA = PR_TRUE; }
+
+  PRPackedBool mDisableSubpixelAA;
 };
 
 void
@@ -4073,8 +4078,11 @@ nsDisplayText::Paint(nsDisplayListBuilder* aBuilder,
   nsRect extraVisible = mVisibleRect;
   nscoord appUnitsPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
   extraVisible.Inflate(appUnitsPerDevPixel, appUnitsPerDevPixel);
-  static_cast<nsTextFrame*>(mFrame)->
-    PaintText(aCtx, ToReferenceFrame(), extraVisible);
+  nsTextFrame* f = static_cast<nsTextFrame*>(mFrame);
+
+  gfxContextAutoDisableSubpixelAntialiasing disable(aCtx->ThebesContext(),
+                                                    mDisableSubpixelAA);
+  f->PaintText(aCtx, ToReferenceFrame(), extraVisible);
 }
 
 NS_IMETHODIMP

layout/xul/base/src/nsTextBoxFrame.cpp

@@ -333,7 +333,9 @@ class nsDisplayXULTextBox : public nsDisplayItem {
 public:
   nsDisplayXULTextBox(nsDisplayListBuilder* aBuilder,
                       nsTextBoxFrame* aFrame) :
-    nsDisplayItem(aBuilder, aFrame) {
+    nsDisplayItem(aBuilder, aFrame),
+    mDisableSubpixelAA(PR_FALSE)
+  {
     MOZ_COUNT_CTOR(nsDisplayXULTextBox);
   }
 #ifdef NS_BUILD_REFCNT_LOGGING
@@ -348,12 +350,18 @@ public:
   NS_DISPLAY_DECL_NAME("XULTextBox", TYPE_XUL_TEXT_BOX)
 
   virtual PRBool HasText() { return PR_TRUE; }
+
+  virtual void DisableComponentAlpha() { mDisableSubpixelAA = PR_TRUE; }
+
+  PRPackedBool mDisableSubpixelAA;
 };
 
 void
 nsDisplayXULTextBox::Paint(nsDisplayListBuilder* aBuilder,
                            nsIRenderingContext* aCtx)
 {
+  gfxContextAutoDisableSubpixelAntialiasing disable(aCtx->ThebesContext(),
+                                                    mDisableSubpixelAA);
   static_cast<nsTextBoxFrame*>(mFrame)->
     PaintTitle(*aCtx, mVisibleRect, ToReferenceFrame());
 }