Bug 1464927 - Make nsImageBoxFrame fallback from WebRender consistently with nsImageFrame. r=tnikkel

Vector images don't support image containers if they are animated. In
order to support this with WebRender, we would need to know when the
generated shared surface was composited, so that we can update the image
container on the next refresh tick. Because images use a different code
path (not ImageClient), we don't have the ability at present. Changing
vector images naively and just updating on every refresh tick if there
is an image container to avoid fallback causes the animation to be very
janky.

Given nsImageFrame is already using fallback properly in this situation,
then we can just fix nsImageBoxFrame to do the same. This gives
acceptable performance without any visible slowness on the animation.

layout/xul/nsImageBoxFrame.cpp

@@ -417,7 +417,7 @@ nsImageBoxFrame::PaintImage(gfxContext& aRenderingContext,
            hasSubRect ? &mSubRect : nullptr);
 }
 
-ImgDrawResult
+Maybe<ImgDrawResult>
 nsImageBoxFrame::CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBuilder,
                                          mozilla::wr::IpcResourceUpdateQueue& aResources,
                                          const StackingContextHelper& aSc,
@@ -433,7 +433,7 @@ nsImageBoxFrame::CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBuild
                                                                 anchorPoint,
                                                                 dest);
   if (!imgCon) {
-    return result;
+    return Nothing();
   }
 
   uint32_t containerFlags = imgIContainer::FLAG_ASYNC_NOTIFY;
@@ -455,7 +455,7 @@ nsImageBoxFrame::CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBuild
     imgCon->GetImageContainerAtSize(aManager, decodeSize, svgContext, containerFlags);
   if (!container) {
     NS_WARNING("Failed to get image container");
-    return ImgDrawResult::NOT_READY;
+    return Nothing();
   }
 
   gfx::IntSize size;
@@ -463,7 +463,7 @@ nsImageBoxFrame::CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBuild
                                                                       aBuilder, aResources,
                                                                       aSc, size, Nothing());
   if (key.isNothing()) {
-    return ImgDrawResult::NOT_READY;
+    return Some(ImgDrawResult::NOT_READY);
   }
   wr::LayoutRect fill = wr::ToRoundedLayoutRect(fillRect);
 
@@ -473,7 +473,7 @@ nsImageBoxFrame::CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBuild
                      wr::ToLayoutSize(fillRect.Size()), wr::ToLayoutSize(gapSize),
                      wr::ToImageRendering(sampleFilter), key.value());
 
-  return ImgDrawResult::SUCCESS;
+  return Some(ImgDrawResult::SUCCESS);
 }
 
 nsRect
@@ -564,10 +564,13 @@ nsDisplayXULImage::CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBui
     flags |= imgIContainer::FLAG_HIGH_QUALITY_SCALING;
   }
 
-  ImgDrawResult result = imageFrame->
+  Maybe<ImgDrawResult> result = imageFrame->
     CreateWebRenderCommands(aBuilder, aResources, aSc, aManager, this, ToReferenceFrame(), flags);
+  if (!result) {
+    return false;
+  }
 
-  nsDisplayItemGenericImageGeometry::UpdateDrawResult(this, result);
+  nsDisplayItemGenericImageGeometry::UpdateDrawResult(this, *result);
   return true;
 }
 

layout/xul/nsImageBoxFrame.h

@@ -96,13 +96,13 @@ public:
                         const nsRect& aDirtyRect,
                         nsPoint aPt, uint32_t aFlags);
 
-  ImgDrawResult CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBuilder,
-                                     mozilla::wr::IpcResourceUpdateQueue& aResources,
-                                     const mozilla::layers::StackingContextHelper& aSc,
-                                     mozilla::layers::WebRenderLayerManager* aManager,
-                                     nsDisplayItem* aItem,
-                                     nsPoint aPt,
-                                     uint32_t aFlags);
+  Maybe<ImgDrawResult> CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBuilder,
+                                               mozilla::wr::IpcResourceUpdateQueue& aResources,
+                                               const mozilla::layers::StackingContextHelper& aSc,
+                                               mozilla::layers::WebRenderLayerManager* aManager,
+                                               nsDisplayItem* aItem,
+                                               nsPoint aPt,
+                                               uint32_t aFlags);
 
   bool CanOptimizeToImageLayer();