Bug 561959. Replace solid-color ThebesLayers with ColorLayers. r=dbaron

layout/base/nsDisplayList.cpp

@@ -346,8 +346,9 @@ nsDisplayList::ComputeVisibility(nsDisplayListBuilder* aBuilder,
     // Record bounds of moving visible items in movingContentAccumulatedBounds.
     // We do not need to add items that are uniform across the entire visible
     // area, since they have no visible movement.
+    nscolor color;
     if (isMoving &&
-        !(item->IsUniform(aBuilder) &&
+        !(item->IsUniform(aBuilder, &color) &&
           bounds.Contains(aVisibleRegion->GetBounds()) &&
           bounds.Contains(aVisibleRegionBeforeMove->GetBounds()))) {
       if (movingContentAccumulatedBounds.IsEmpty()) {
@@ -570,6 +571,28 @@ CreateEmptyThebesLayer(nsDisplayListBuilder* aBuilder,
   return itemGroup;
 }
 
+static PRBool
+IsAllUniform(nsDisplayListBuilder* aBuilder, nsDisplayList::ItemGroup* aGroup,
+             nscolor* aColor)
+{
+  nsRect visibleRect = aGroup->mStartItem->GetVisibleRect();
+  nscolor finalColor = NS_RGBA(0,0,0,0);
+  for (nsDisplayList::ItemGroup* group = aGroup; group;
+       group = group->mNextItemsForLayer) {
+    for (nsDisplayItem* item = group->mStartItem; item != group->mEndItem;
+         item = item->GetAbove()) {
+      nscolor color;
+      if (visibleRect != item->GetVisibleRect())
+        return PR_FALSE;
+      if (!item->IsUniform(aBuilder, &color))
+        return PR_FALSE;
+      finalColor = NS_ComposeColors(finalColor, color);
+    }
+  }
+  *aColor = finalColor;
+  return PR_TRUE;
+}
+
 /**
  * This is the heart of layout's integration with layers. We
  * use a ClippedItemIterator to iterate through descendant display
@@ -681,6 +704,15 @@ void nsDisplayList::BuildLayers(nsDisplayListBuilder* aBuilder,
   for (PRUint32 i = 0; i < aLayers->Length(); ++i) {
     LayerItems* layerItems = &aLayers->ElementAt(i);
 
+    nscolor color;
+    if (layerItems->mThebesLayer &&
+        IsAllUniform(aBuilder, layerItems->mItems, &color)) {
+      layerItems->mThebesLayer = nsnull;
+      nsRefPtr<ColorLayer> layer = aManager->CreateColorLayer();
+      layer->SetColor(gfxRGBA(color));
+      layerItems->mLayer = layer.forget();
+    }
+
     gfxMatrix transform;
     nsIntRect visibleRect = layerItems->mVisibleRect;
     if (layerItems->mLayer->GetTransform().Is2D(&transform)) {
@@ -1099,7 +1131,7 @@ nsDisplayBackground::IsOpaque(nsDisplayListBuilder* aBuilder) {
 }
 
 PRBool
-nsDisplayBackground::IsUniform(nsDisplayListBuilder* aBuilder) {
+nsDisplayBackground::IsUniform(nsDisplayListBuilder* aBuilder, nscolor* aColor) {
   // theme background overrides any other background
   if (mIsThemed)
     return PR_FALSE;
@@ -1107,14 +1139,18 @@ nsDisplayBackground::IsUniform(nsDisplayListBuilder* aBuilder) {
   nsStyleContext *bgSC;
   PRBool hasBG =
     nsCSSRendering::FindBackground(mFrame->PresContext(), mFrame, &bgSC);
-  if (!hasBG)
+  if (!hasBG) {
+    aColor = NS_RGBA(0,0,0,0);
     return PR_TRUE;
+  }
   const nsStyleBackground* bg = bgSC->GetStyleBackground();
   if (bg->BottomLayer().mImage.IsEmpty() &&
       bg->mImageCount == 1 &&
       !nsLayoutUtils::HasNonZeroCorner(mFrame->GetStyleBorder()->mBorderRadius) &&
-      bg->BottomLayer().mClip == NS_STYLE_BG_CLIP_BORDER)
+      bg->BottomLayer().mClip == NS_STYLE_BG_CLIP_BORDER) {
+    *aColor = bg->mBackgroundColor;
     return PR_TRUE;
+  }
   return PR_FALSE;
 }
 
@@ -1426,7 +1462,7 @@ nsDisplayWrapList::IsOpaque(nsDisplayListBuilder* aBuilder) {
   return PR_FALSE;
 }
 
-PRBool nsDisplayWrapList::IsUniform(nsDisplayListBuilder* aBuilder) {
+PRBool nsDisplayWrapList::IsUniform(nsDisplayListBuilder* aBuilder, nscolor* aColor) {
   // We could try to do something but let's conservatively just return PR_FALSE.
   return PR_FALSE;
 }
@@ -1996,12 +2032,12 @@ PRBool nsDisplayTransform::IsOpaque(nsDisplayListBuilder *aBuilder)
  * wrapped list is uniform.  See IsOpaque for discussion of why this
  * works.
  */
-PRBool nsDisplayTransform::IsUniform(nsDisplayListBuilder *aBuilder)
+PRBool nsDisplayTransform::IsUniform(nsDisplayListBuilder *aBuilder, nscolor* aColor)
 {
   const nsStyleDisplay* disp = mFrame->GetStyleDisplay();
   return disp->mTransform.GetMainMatrixEntry(1) == 0.0f &&
     disp->mTransform.GetMainMatrixEntry(2) == 0.0f &&
-    mStoredList.IsUniform(aBuilder);
+    mStoredList.IsUniform(aBuilder, aColor);
 }
 
 /* If UNIFIED_CONTINUATIONS is defined, we can merge two display lists that

layout/base/nsDisplayList.h

@@ -544,10 +544,11 @@ public:
    */
   virtual PRBool IsOpaque(nsDisplayListBuilder* aBuilder) { return PR_FALSE; }
   /**
+   * If this returns true, then aColor is set to the uniform color
    * @return PR_TRUE if the item is guaranteed to paint every pixel in its
    * bounds with the same (possibly translucent) color
    */
-  virtual PRBool IsUniform(nsDisplayListBuilder* aBuilder) { return PR_FALSE; }
+  virtual PRBool IsUniform(nsDisplayListBuilder* aBuilder, nscolor* aColor) { return PR_FALSE; }
   /**
    * @return PR_FALSE if the painting performed by the item is invariant
    * when frame aFrame is moved relative to aBuilder->GetRootMovingFrame().
@@ -628,6 +629,8 @@ public:
    * list.
    */
   virtual nsDisplayList* GetList() { return nsnull; }
+
+  const nsRect& GetVisibleRect() { return mVisibleRect; }
   
 #ifdef NS_DEBUG
   /**
@@ -1303,7 +1306,11 @@ public:
     return (NS_GET_A(mColor) == 255);
   }
 
-  virtual PRBool IsUniform(nsDisplayListBuilder* aBuilder) { return PR_TRUE; }
+  virtual PRBool IsUniform(nsDisplayListBuilder* aBuilder, nscolor* aColor)
+  {
+    *aColor = mColor;
+    return PR_TRUE;
+  }
 
   virtual void Paint(nsDisplayListBuilder* aBuilder, nsIRenderingContext* aCtx);
 
@@ -1335,7 +1342,7 @@ public:
   }
   virtual PRBool IsOpaque(nsDisplayListBuilder* aBuilder);
   virtual PRBool IsVaryingRelativeToMovingFrame(nsDisplayListBuilder* aBuilder);
-  virtual PRBool IsUniform(nsDisplayListBuilder* aBuilder);
+  virtual PRBool IsUniform(nsDisplayListBuilder* aBuilder, nscolor* aColor);
   virtual nsRect GetBounds(nsDisplayListBuilder* aBuilder);
   virtual void Paint(nsDisplayListBuilder* aBuilder, nsIRenderingContext* aCtx);
   NS_DISPLAY_DECL_NAME("Background")
@@ -1468,7 +1475,7 @@ public:
                        HitTestState* aState, nsTArray<nsIFrame*> *aOutFrames);
   virtual nsRect GetBounds(nsDisplayListBuilder* aBuilder);
   virtual PRBool IsOpaque(nsDisplayListBuilder* aBuilder);
-  virtual PRBool IsUniform(nsDisplayListBuilder* aBuilder);
+  virtual PRBool IsUniform(nsDisplayListBuilder* aBuilder, nscolor* aColor);
   virtual PRBool IsVaryingRelativeToMovingFrame(nsDisplayListBuilder* aBuilder);
   virtual void Paint(nsDisplayListBuilder* aBuilder, nsIRenderingContext* aCtx);
   virtual PRBool ComputeVisibility(nsDisplayListBuilder* aBuilder,
@@ -1672,7 +1679,7 @@ public:
                        HitTestState *aState, nsTArray<nsIFrame*> *aOutFrames);
   virtual nsRect GetBounds(nsDisplayListBuilder *aBuilder);
   virtual PRBool IsOpaque(nsDisplayListBuilder *aBuilder);
-  virtual PRBool IsUniform(nsDisplayListBuilder *aBuilder);
+  virtual PRBool IsUniform(nsDisplayListBuilder *aBuilder, nscolor* aColor);
   virtual void   Paint(nsDisplayListBuilder *aBuilder,
                        nsIRenderingContext *aCtx);
   virtual PRBool ComputeVisibility(nsDisplayListBuilder *aBuilder,

layout/base/nsLayoutDebugger.cpp

@@ -172,11 +172,12 @@ PrintDisplayListTo(nsDisplayListBuilder* aBuilder, const nsDisplayList& aList,
       default:
         break;
     }
+    nscolor color;
     fprintf(aOutput, "%s %p(%s) (%d,%d,%d,%d)%s%s%s%s\n", i->Name(),
             (void*)f, NS_ConvertUTF16toUTF8(fName).get(),
             rect.x, rect.y, rect.width, rect.height,
             i->IsOpaque(aBuilder) ? " opaque" : "",
-            i->IsUniform(aBuilder) ? " uniform" : "",
+            i->IsUniform(aBuilder, &color) ? " uniform" : "",
             f && aBuilder->IsMovingFrame(f) ? " moving" : "",
             f && aBuilder->IsMovingFrame(f) && !i->GetList() &&
               i->IsVaryingRelativeToMovingFrame(aBuilder) ? " varying" : "");

layout/base/nsLayoutUtils.cpp

@@ -1388,7 +1388,8 @@ AddItemsToRegion(nsDisplayListBuilder* aBuilder, nsDisplayList* aList,
           }
         } else {
           // not moving.
-          if (item->IsUniform(aBuilder)) {
+          nscolor color;
+          if (item->IsUniform(aBuilder, &color)) {
             // If it's uniform, we don't need to invalidate where one part
             // of the item was copied to another part.
             exclude.IntersectRect(r, r + aDelta);