Bug 1022612. Part 43: Fix up SuppressComponentAlpha to allow component alpha in inactive layers over opaque parts of the chrome window. r=mattwoodrow

--HG--
extra : rebase_source : a15fb640c4fe7917321bcea5cdf2dc5e6087a140

layout/base/FrameLayerBuilder.cpp

@@ -2212,21 +2212,22 @@ ContainerState::PopThebesLayerData()
 }
 
 static bool
-SuppressComponentAlpha(nsDisplayListBuilder* aBuilder,
-                       nsDisplayItem* aItem)
+IsItemAreaInWindowOpaqueRegion(nsDisplayListBuilder* aBuilder,
+                               nsDisplayItem* aItem,
+                               const nsRect& aComponentAlphaBounds)
 {
-  // Suppress component alpha for items in the toplevel window chrome that
-  // aren't transformed.
-  nsIFrame* f = aItem->Frame();
-  nsIFrame* ref = aBuilder->RootReferenceFrame();
-  if (f->PresContext() != ref->PresContext())
-    return false;
-
-  for (nsIFrame* t = f; t; t = t->GetParent()) {
-    if (t->IsTransformed())
-      return false;
+  if (!aItem->Frame()->PresContext()->IsChrome()) {
+    // Assume that Web content is always in the window opaque region.
+    return true;
   }
-  return true;
+  if (aItem->ReferenceFrame() != aBuilder->RootReferenceFrame()) {
+    // aItem is probably in some transformed subtree.
+    // We're not going to bother figuring out where this landed, we're just
+    // going to assume it might have landed over a transparent part of
+    // the window.
+    return false;
+  }
+  return aBuilder->GetWindowOpaqueRegion().Contains(aComponentAlphaBounds);
 }
 
 void
@@ -2338,10 +2339,11 @@ ThebesLayerData::Accumulate(ContainerState* aState,
       nsIntRect componentAlphaRect =
         aState->ScaleToOutsidePixels(componentAlpha, false).Intersect(aVisibleRect);
       if (!mOpaqueRegion.Contains(componentAlphaRect)) {
-        if (SuppressComponentAlpha(aState->mBuilder, aItem)) {
-          aItem->DisableComponentAlpha();
-        } else {
+        if (IsItemAreaInWindowOpaqueRegion(aState->mBuilder, aItem,
+              componentAlpha.Intersect(aItem->GetVisibleRect()))) {
           mNeedComponentAlpha = true;
+        } else {
+          aItem->DisableComponentAlpha();
         }
       }
     }
@@ -2603,8 +2605,8 @@ ContainerState::ComputeOpaqueRect(nsDisplayItem* aItem,
     // Add opaque areas to the "exclude glass" region. Only do this for
     // ThebesLayers which are direct children of the root layer; this means
     // they can't have transforms or opacity wrapping them.
-    if (!mContainerLayer->GetParent() && mBuilder->HasGlass()) {
-      mBuilder->AddExcludedGlassRegion(opaqueClipped);
+    if (!mContainerLayer->GetParent()) {
+      mBuilder->AddWindowOpaqueRegion(opaqueClipped);
     }
     opaquePixels = ScaleRegionToInsidePixels(opaqueClipped, snapOpaque);
     if (aFixedPosFrame && ItemCoversScrollableArea(aItem, opaque)) {

layout/base/nsDisplayList.h

@@ -667,11 +667,15 @@ public:
    * -moz-win-exclude-glass style. Used in setting glass margins on
    * Windows.
    */  
-  void AddExcludedGlassRegion(const nsRegion& bounds) {
-    mExcludedGlassRegion.Or(mExcludedGlassRegion, bounds);
+  void AddWindowOpaqueRegion(const nsRegion& bounds) {
+    mWindowOpaqueRegion.Or(mWindowOpaqueRegion, bounds);
   }
-  const nsRegion& GetExcludedGlassRegion() {
-    return mExcludedGlassRegion;
+  /**
+   * Returns the window opaque region built so far. This may be incomplete
+   * since the opaque region is built during layer construction.
+   */
+  const nsRegion& GetWindowOpaqueRegion() {
+    return mWindowOpaqueRegion;
   }
   void SetGlassDisplayItem(nsDisplayItem* aItem) {
     if (mGlassDisplayItem) {
@@ -684,10 +688,6 @@ public:
       mGlassDisplayItem = aItem;
     }
   }
-  // Call this only after we've finished building the display list
-  bool HasGlass() {
-    return mGlassDisplayItem != nullptr;
-  }
   bool NeedToForceTransparentSurfaceForItem(nsDisplayItem* aItem) {
     return aItem == mGlassDisplayItem;
   }
@@ -747,7 +747,7 @@ private:
   nsPoint                        mCurrentOffsetToReferenceFrame;
   // Relative to mCurrentFrame.
   nsRect                         mDirtyRect;
-  nsRegion                       mExcludedGlassRegion;
+  nsRegion                       mWindowOpaqueRegion;
   // The display item for the Windows window glass background, if any
   nsDisplayItem*                 mGlassDisplayItem;
   nsTArray<DisplayItemClip*>     mDisplayItemClipsToDestroy;

layout/base/nsLayoutUtils.cpp

@@ -3021,7 +3021,7 @@ nsLayoutUtils::PaintFrame(nsRenderingContext* aRenderingContext, nsIFrame* aFram
       !(aFlags & PAINT_DOCUMENT_RELATIVE)) {
     nsIWidget *widget = aFrame->GetNearestWidget();
     if (widget) {
-      nsRegion excludedRegion = builder.GetExcludedGlassRegion();
+      nsRegion excludedRegion = builder.GetWindowOpaqueRegion();
       nsIntRegion windowRegion(excludedRegion.ToNearestPixels(presContext->AppUnitsPerDevPixel()));
       widget->UpdateOpaqueRegion(windowRegion);
     }

layout/xul/nsBoxFrame.cpp

@@ -1320,8 +1320,8 @@ nsBoxFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
     // in calculating glass margins on Windows.
     const nsStyleDisplay* styles = StyleDisplay();
     if (styles && styles->mAppearance == NS_THEME_WIN_EXCLUDE_GLASS) {
-      nsRect rect = nsRect(aBuilder->ToReferenceFrame(this), GetSize());
-      aBuilder->AddExcludedGlassRegion(rect);
+      aBuilder->AddWindowOpaqueRegion(
+          nsRect(aBuilder->ToReferenceFrame(this), GetSize()));
     }
   }