From 083b9cd7fcd00b6394c090956923f0678687332a Mon Sep 17 00:00:00 2001
From: Matt Woodrow <mwoodrow@mozilla.com>
Date: Fri, 22 Apr 2016 17:50:11 +1200
Subject: [PATCH] Bug 1265256 - Use the canvas positioning area when computing
 the background-attachment:fixed rect for canvas frames. r=mstange

---
 layout/base/nsDisplayList.cpp    | 24 ---------------------
 layout/base/nsDisplayList.h      |  3 ---
 layout/generic/nsCanvasFrame.cpp | 36 ++++++++++++++++++++++++++++++++
 layout/generic/nsCanvasFrame.h   |  4 ++++
 4 files changed, 40 insertions(+), 27 deletions(-)

diff --git a/layout/base/nsDisplayList.cpp b/layout/base/nsDisplayList.cpp
index c297cded396c..1683c44e033c 100644
--- a/layout/base/nsDisplayList.cpp
+++ b/layout/base/nsDisplayList.cpp
@@ -2586,30 +2586,6 @@ nsDisplayBackgroundImage::ComputeShouldTreatAsFixed(bool isTransformedFixed) con
   return !isTransformedFixed;
 }
 
-bool
-nsDisplayBackgroundImage::IsSingleFixedPositionImage(nsDisplayListBuilder* aBuilder,
-                                                     const nsRect& aClipRect,
-                                                     gfxRect* aDestRect)
-{
-  if (!mBackgroundStyle)
-    return false;
-
-  if (mBackgroundStyle->mImage.mLayers.Length() != 1)
-    return false;
-
-  if (!ShouldTreatAsFixed())
-    return false;
-
-  // We only care about images here, not gradients.
-  if (!mIsRasterImage)
-    return false;
-
-  int32_t appUnitsPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
-  *aDestRect = nsLayoutUtils::RectToGfxRect(mFillRect, appUnitsPerDevPixel);
-
-  return true;
-}
-
 bool
 nsDisplayBackgroundImage::IsNonEmptyFixedImage() const
 {
diff --git a/layout/base/nsDisplayList.h b/layout/base/nsDisplayList.h
index 7d1f10ebf3f7..2c7cc2336b51 100644
--- a/layout/base/nsDisplayList.h
+++ b/layout/base/nsDisplayList.h
@@ -2736,9 +2736,6 @@ protected:
   typedef class mozilla::layers::ImageLayer ImageLayer;
 
   bool TryOptimizeToImageLayer(LayerManager* aManager, nsDisplayListBuilder* aBuilder);
-  bool IsSingleFixedPositionImage(nsDisplayListBuilder* aBuilder,
-                                  const nsRect& aClipRect,
-                                  gfxRect* aDestRect);
   bool IsNonEmptyFixedImage() const;
   nsRect GetBoundsInternal(nsDisplayListBuilder* aBuilder);
   bool ShouldTreatAsFixed() const;
diff --git a/layout/generic/nsCanvasFrame.cpp b/layout/generic/nsCanvasFrame.cpp
index 1b279364dc92..301033efd90b 100644
--- a/layout/generic/nsCanvasFrame.cpp
+++ b/layout/generic/nsCanvasFrame.cpp
@@ -326,6 +326,42 @@ nsDisplayCanvasBackgroundImage::Paint(nsDisplayListBuilder* aBuilder,
   PaintInternal(aBuilder, aCtx, mVisibleRect, &bgClipRect);
 }
 
+bool
+nsDisplayCanvasBackgroundImage::IsSingleFixedPositionImage(nsDisplayListBuilder* aBuilder,
+                                                           const nsRect& aClipRect,
+                                                           gfxRect* aDestRect)
+{
+  if (!mBackgroundStyle)
+    return false;
+
+  if (mBackgroundStyle->mImage.mLayers.Length() != 1)
+    return false;
+
+
+  nsPresContext* presContext = mFrame->PresContext();
+  uint32_t flags = aBuilder->GetBackgroundPaintFlags();
+  nsRect borderArea = nsRect(ToReferenceFrame(), mFrame->GetSize());
+  const nsStyleImageLayers::Layer &layer = mBackgroundStyle->mImage.mLayers[mLayer];
+
+  if (layer.mAttachment != NS_STYLE_IMAGELAYER_ATTACHMENT_FIXED)
+    return false;
+
+   nsBackgroundLayerState state =
+     nsCSSRendering::PrepareImageLayer(presContext, mFrame, flags,
+                                       borderArea, aClipRect, layer);
+
+
+  // We only care about images here, not gradients.
+  if (!mIsRasterImage)
+    return false;
+
+  int32_t appUnitsPerDevPixel = presContext->AppUnitsPerDevPixel();
+  *aDestRect = nsLayoutUtils::RectToGfxRect(state.mFillArea, appUnitsPerDevPixel);
+
+  return true;
+}
+
+
 void
 nsDisplayCanvasThemedBackground::Paint(nsDisplayListBuilder* aBuilder,
                                        nsRenderingContext* aCtx)
diff --git a/layout/generic/nsCanvasFrame.h b/layout/generic/nsCanvasFrame.h
index 5b628be78f37..d22389737cde 100644
--- a/layout/generic/nsCanvasFrame.h
+++ b/layout/generic/nsCanvasFrame.h
@@ -227,6 +227,10 @@ public:
   // We still need to paint a background color as well as an image for this item, 
   // so we can't support this yet.
   virtual bool SupportsOptimizingToImage() override { return false; }
+
+ bool IsSingleFixedPositionImage(nsDisplayListBuilder* aBuilder,
+                                  const nsRect& aClipRect,
+                                  gfxRect* aDestRect);
   
   
   NS_DISPLAY_DECL_NAME("CanvasBackgroundImage", TYPE_CANVAS_BACKGROUND_IMAGE)