Bug 579276. Part 7: Don't retain transparent layers that would hurt text rendering. r=cjones

gfx/layers/basic/BasicLayers.cpp

@@ -367,6 +367,23 @@ InheritContextFlags(gfxContext* aSource, gfxContext* aDest)
   }
 }
 
+static PRBool
+ShouldRetainTransparentSurface(PRUint32 aContentFlags,
+                               gfxASurface* aTargetSurface)
+{
+  if (aContentFlags & Layer::CONTENT_NO_TEXT)
+    return PR_TRUE;
+
+  switch (aTargetSurface->GetTextQualityInTransparentSurfaces()) {
+  case gfxASurface::TEXT_QUALITY_OK:
+    return PR_TRUE;
+  case gfxASurface::TEXT_QUALITY_OK_OVER_OPAQUE_PIXELS:
+    return (aContentFlags & Layer::CONTENT_NO_TEXT_OVER_TRANSPARENT) != 0;
+  default:
+    return PR_FALSE;
+  }
+}
+
 void
 BasicThebesLayer::Paint(gfxContext* aContext,
                         LayerManager::DrawThebesLayerCallback aCallback,
@@ -377,15 +394,20 @@ BasicThebesLayer::Paint(gfxContext* aContext,
                "Can only draw in drawing phase");
   gfxContext* target = BasicManager()->GetTarget();
   NS_ASSERTION(target, "We shouldn't be called if there's no target");
+  nsRefPtr<gfxASurface> targetSurface = aContext->CurrentSurface();
+
+  PRBool canUseOpaqueSurface = CanUseOpaqueSurface();
+  if (!BasicManager()->IsRetained() ||
+      (aOpacity == 1.0 && !canUseOpaqueSurface &&
+       !ShouldRetainTransparentSurface(mContentFlags, targetSurface))) {
+    mValidRegion.SetEmpty();
+    mBuffer.Clear();
 
-  if (!BasicManager()->IsRetained()) {
     if (aOpacity != 1.0) {
       target->Save();
       ClipToContain(target, mVisibleRegion.GetBounds());
       target->PushGroup(gfxASurface::CONTENT_COLOR_ALPHA);
     }
-    mValidRegion.SetEmpty();
-    mBuffer.Clear();
     aCallback(this, target, mVisibleRegion, nsIntRegion(), aCallbackData);
     if (aOpacity != 1.0) {
       target->PopGroupToSource();
@@ -395,15 +417,12 @@ BasicThebesLayer::Paint(gfxContext* aContext,
     return;
   }
 
-  nsRefPtr<gfxASurface> targetSurface = aContext->CurrentSurface();
-  PRBool isOpaqueContent =
-    (targetSurface->AreSimilarSurfacesSensitiveToContentType() &&
-     aOpacity == 1.0 &&
-     CanUseOpaqueSurface());
   {
+    PRBool opaqueBuffer = canUseOpaqueSurface &&
+      targetSurface->AreSimilarSurfacesSensitiveToContentType();
     Buffer::ContentType contentType =
-      isOpaqueContent ? gfxASurface::CONTENT_COLOR :
-                        gfxASurface::CONTENT_COLOR_ALPHA;
+      opaqueBuffer ? gfxASurface::CONTENT_COLOR :
+                     gfxASurface::CONTENT_COLOR_ALPHA;
     Buffer::PaintState state = mBuffer.BeginPaint(this, contentType);
     mValidRegion.Sub(mValidRegion, state.mRegionToInvalidate);
 
@@ -425,7 +444,7 @@ BasicThebesLayer::Paint(gfxContext* aContext,
     }
   }
 
-  mBuffer.DrawTo(this, isOpaqueContent, target, aOpacity);
+  mBuffer.DrawTo(this, canUseOpaqueSurface, target, aOpacity);
 }
 
 void