Bug 1321412 - Change the return type of ShouldPrerenderTransformedContent() to an enum. r=mattwoodrow

MozReview-Commit-ID: EMTdW46D8cM

--HG--
extra : rebase_source : 1ecd8fd39a1d3bc74200dbe4f53dd78eda57987e

layout/generic/nsFrame.cpp

@@ -2208,11 +2208,14 @@ nsIFrame::BuildDisplayListForStackingContext(nsDisplayListBuilder* aBuilder,
   bool allowAsyncAnimation = false;
   if (isTransformed) {
     const nsRect overflow = GetVisualOverflowRectRelativeToSelf();
-    if (nsDisplayTransform::ShouldPrerenderTransformedContent(aBuilder,
-                                                              this)) {
+    nsDisplayTransform::PrerenderDecision decision =
+        nsDisplayTransform::ShouldPrerenderTransformedContent(aBuilder, this);
+    switch (decision) {
+    case nsDisplayTransform::FullPrerender:
       dirtyRect = overflow;
       allowAsyncAnimation = true;
-    } else {
+      break;
+    case nsDisplayTransform::NoPrerender:
       if (overflow.IsEmpty() && !extend3DContext) {
         return;
       }

layout/painting/nsDisplayList.cpp

@@ -6226,9 +6226,9 @@ nsDisplayTransform::CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder)
   return mAllowAsyncAnimation;
 }
 
-/* static */ bool
+/* static */ auto
 nsDisplayTransform::ShouldPrerenderTransformedContent(nsDisplayListBuilder* aBuilder,
-                                                      nsIFrame* aFrame)
+                                                      nsIFrame* aFrame) -> PrerenderDecision
 {
   // Elements whose transform has been modified recently, or which
   // have a compositor-animated transform, can be prerendered. An element
@@ -6242,7 +6242,7 @@ nsDisplayTransform::ShouldPrerenderTransformedContent(nsDisplayListBuilder* aBui
       AnimationPerformanceWarning(
         AnimationPerformanceWarning::Type::TransformFrameInactive));
 
-    return false;
+    return NoPrerender;
   }
 
   nsSize refSize = aBuilder->RootReferenceFrame()->GetSize();
@@ -6258,7 +6258,7 @@ nsDisplayTransform::ShouldPrerenderTransformedContent(nsDisplayListBuilder* aBui
   if (frameSize <= refSize) {
     maxInAppUnits = aFrame->PresContext()->DevPixelsToAppUnits(4096);
     if (frameSize <= nsSize(maxInAppUnits, maxInAppUnits)) {
-      return true;
+      return FullPrerender;
     }
   }
 
@@ -6278,7 +6278,7 @@ nsDisplayTransform::ShouldPrerenderTransformedContent(nsDisplayListBuilder* aBui
         nsPresContext::AppUnitsToIntCSSPixels(visual.height),
         nsPresContext::AppUnitsToIntCSSPixels(maxInAppUnits)
       }));
-  return false;
+  return NoPrerender;
 }
 
 /* If the matrix is singular, or a hidden backface is shown, the frame won't be visible or hit. */

layout/painting/nsDisplayList.h

@@ -4063,6 +4063,11 @@ class nsDisplayTransform: public nsDisplayItem
   };
 
 public:
+  enum PrerenderDecision {
+    NoPrerender,
+    FullPrerender
+  };
+
   /**
    * Returns a matrix (in pixels) for the current frame. The matrix should be relative to
    * the current frame's coordinate space.
@@ -4276,11 +4281,11 @@ public:
                                                uint32_t aFlags,
                                                const nsRect* aBoundsOverride = nullptr);
   /**
-   * Return true when we should try to prerender the entire contents of the
+   * Return FullPrerender when we should try to prerender the entire contents of the
    * transformed frame even when it's not completely visible (yet).
    */
-  static bool ShouldPrerenderTransformedContent(nsDisplayListBuilder* aBuilder,
-                                                nsIFrame* aFrame);
+  static PrerenderDecision ShouldPrerenderTransformedContent(nsDisplayListBuilder* aBuilder,
+                                                             nsIFrame* aFrame);
   bool CanUseAsyncAnimations(nsDisplayListBuilder* aBuilder) override;
 
   bool MayBeAnimated(nsDisplayListBuilder* aBuilder);