Bug 1321412 - Allow ShouldPrerenderTransformedContent() to override the dirty rect. r=mattwoodrow

MozReview-Commit-ID: 5EpiANOynwP

--HG--
extra : rebase_source : d2bd3668bbe12b3853327f2c41e6a77acf1bbadd

layout/generic/nsFrame.cpp

@@ -2209,10 +2209,9 @@ nsIFrame::BuildDisplayListForStackingContext(nsDisplayListBuilder* aBuilder,
   if (isTransformed) {
     const nsRect overflow = GetVisualOverflowRectRelativeToSelf();
     nsDisplayTransform::PrerenderDecision decision =
-        nsDisplayTransform::ShouldPrerenderTransformedContent(aBuilder, this);
+        nsDisplayTransform::ShouldPrerenderTransformedContent(aBuilder, this, &dirtyRect);
     switch (decision) {
     case nsDisplayTransform::FullPrerender:
-      dirtyRect = overflow;
       allowAsyncAnimation = true;
       break;
     case nsDisplayTransform::NoPrerender:

layout/painting/nsDisplayList.cpp

@@ -6228,7 +6228,8 @@ nsDisplayTransform::CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder)
 
 /* static */ auto
 nsDisplayTransform::ShouldPrerenderTransformedContent(nsDisplayListBuilder* aBuilder,
-                                                      nsIFrame* aFrame) -> PrerenderDecision
+                                                      nsIFrame* aFrame,
+                                                      nsRect* aDirtyRect) -> PrerenderDecision
 {
   // Elements whose transform has been modified recently, or which
   // have a compositor-animated transform, can be prerendered. An element
@@ -6251,13 +6252,14 @@ nsDisplayTransform::ShouldPrerenderTransformedContent(nsDisplayListBuilder* aBui
   // for shadows, borders, etc.
   refSize += nsSize(refSize.width / 8, refSize.height / 8);
   gfxSize scale = nsLayoutUtils::GetTransformToAncestorScale(aFrame);
-  nsSize frameSize = nsSize(
-    aFrame->GetVisualOverflowRectRelativeToSelf().Size().width * scale.width,
-    aFrame->GetVisualOverflowRectRelativeToSelf().Size().height * scale.height);
+  nsRect overflow = aFrame->GetVisualOverflowRectRelativeToSelf();
+  nsSize frameSize = nsSize(overflow.Size().width * scale.width,
+                            overflow.Size().height * scale.height);
   nscoord maxInAppUnits = nscoord_MAX;
   if (frameSize <= refSize) {
     maxInAppUnits = aFrame->PresContext()->DevPixelsToAppUnits(4096);
     if (frameSize <= nsSize(maxInAppUnits, maxInAppUnits)) {
+      *aDirtyRect = overflow;
       return FullPrerender;
     }
   }

layout/painting/nsDisplayList.h

@@ -4283,9 +4283,11 @@ public:
   /**
    * Return FullPrerender when we should try to prerender the entire contents of the
    * transformed frame even when it's not completely visible (yet).
+   * |aDirtyRect| is updated to the area that should be prerendered.
    */
   static PrerenderDecision ShouldPrerenderTransformedContent(nsDisplayListBuilder* aBuilder,
-                                                             nsIFrame* aFrame);
+                                                             nsIFrame* aFrame,
+                                                             nsRect* aDirtyRect);
   bool CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder) override;
 
   bool MayBeAnimated(nsDisplayListBuilder* aBuilder);