Bug 945634. The fixed-pos anchor point should be in the layer's coordinate system, whose 0,0 is the top-left of the fixed-pos frame. r=mattwoodrow

gfx/layers/Layers.cpp

@@ -1276,7 +1276,8 @@ Layer::PrintInfo(nsACString& aTo, const char* aPrefix)
     }
   }
   if (GetIsFixedPosition()) {
-    aTo.AppendPrintf(" [isFixedPosition anchor=%f,%f]", mAnchor.x, mAnchor.y);
+    aTo.AppendPrintf(" [isFixedPosition anchor=%f,%f margin=%f,%f,%f,%f]", mAnchor.x, mAnchor.y,
+                     mMargins.top, mMargins.right, mMargins.bottom, mMargins.left);
   }
   if (GetIsStickyPosition()) {
     aTo.AppendPrintf(" [isStickyPosition scrollId=%d outer=%f,%f %fx%f "

layout/base/FrameLayerBuilder.cpp

@@ -1674,8 +1674,7 @@ ContainerState::SetFixedPositionLayerData(Layer* aLayer,
   }
 
   nsLayoutUtils::SetFixedPositionLayerData(aLayer,
-      viewportFrame, viewportSize, aFixedPosFrame, mContainerReferenceFrame,
-      presContext, mParameters);
+      viewportFrame, viewportSize, aFixedPosFrame, presContext, mParameters);
 }
 
 void

layout/base/nsDisplayList.cpp

@@ -3363,9 +3363,8 @@ nsDisplayStickyPosition::BuildLayer(nsDisplayListBuilder* aBuilder,
   }
 
   nsLayoutUtils::SetFixedPositionLayerData(layer, scrollFrame, scrollFrameSize,
-                                           mStickyPosFrame, ReferenceFrame(),
-                                           presContext,
-                                           aContainerParameters);
+                                           mStickyPosFrame,
+                                           presContext, aContainerParameters);
 
   ViewID scrollId = nsLayoutUtils::FindOrCreateIDFor(
     stickyScrollContainer->ScrollFrame()->GetScrolledFrame()->GetContent());

layout/base/nsLayoutUtils.cpp

@@ -1204,14 +1204,13 @@ nsLayoutUtils::SetFixedPositionLayerData(Layer* aLayer,
                                          const nsIFrame* aViewportFrame,
                                          nsSize aViewportSize,
                                          const nsIFrame* aFixedPosFrame,
-                                         const nsIFrame* aReferenceFrame,
                                          nsPresContext* aPresContext,
                                          const ContainerLayerParameters& aContainerParameters) {
   // Find out the rect of the viewport frame relative to the reference frame.
   // This, in conjunction with the container scale, will correspond to the
   // coordinate-space of the built layer.
   float factor = aPresContext->AppUnitsPerDevPixel();
-  nsPoint origin = aViewportFrame->GetOffsetToCrossDoc(aReferenceFrame);
+  nsPoint origin = aViewportFrame->GetOffsetToCrossDoc(aFixedPosFrame);
   LayerRect anchorRect(NSAppUnitsToFloatPixels(origin.x, factor) *
                          aContainerParameters.mXScale,
                        NSAppUnitsToFloatPixels(origin.y, factor) *

layout/base/nsLayoutUtils.h

@@ -378,7 +378,6 @@ public:
   static void SetFixedPositionLayerData(Layer* aLayer, const nsIFrame* aViewportFrame,
                                         nsSize aViewportSize,
                                         const nsIFrame* aFixedPosFrame,
-                                        const nsIFrame* aReferenceFrame,
                                         nsPresContext* aPresContext,
                                         const ContainerLayerParameters& aContainerParameters);