Bug 1104036 - Make -moz-window-dragging work in rectilinear 2d transforms. r=roc

layout/base/nsDisplayList.cpp

@@ -1236,10 +1236,31 @@ nsDisplayListBuilder::RecomputeCurrentAnimatedGeometryRoot()
 void
 nsDisplayListBuilder::AdjustWindowDraggingRegion(nsIFrame* aFrame)
 {
-  if (!IsForPainting() || IsInSubdocument() || IsInTransform()) {
+  if (!IsForPainting() || IsInSubdocument()) {
     return;
   }
 
+  Matrix4x4 referenceFrameToRootReferenceFrame;
+
+  // The const_cast is for nsLayoutUtils::GetTransformToAncestor.
+  nsIFrame* referenceFrame = const_cast<nsIFrame*>(FindReferenceFrameFor(aFrame));
+
+  if (IsInTransform()) {
+    // Only support 2d rectilinear transforms. Transform support is needed for
+    // the horizontal flip transform that's applied to the urlbar textbox in
+    // RTL mode - it should be able to exclude itself from the draggable region.
+    referenceFrameToRootReferenceFrame =
+      nsLayoutUtils::GetTransformToAncestor(referenceFrame, mReferenceFrame);
+    Matrix referenceFrameToRootReferenceFrame2d;
+    if (!referenceFrameToRootReferenceFrame.Is2D(&referenceFrameToRootReferenceFrame2d) ||
+        !referenceFrameToRootReferenceFrame2d.IsRectilinear()) {
+      return;
+    }
+  } else {
+    MOZ_ASSERT(referenceFrame == mReferenceFrame,
+               "referenceFrameToRootReferenceFrame needs to be adjusted");
+  }
+
   // We do some basic visibility checking on the frame's border box here.
   // We intersect it both with the current dirty rect and with the current
   // clip. Either one is just a conservative approximation on its own, but
@@ -1260,11 +1281,19 @@ nsDisplayListBuilder::AdjustWindowDraggingRegion(nsIFrame* aFrame)
     borderBox = clip->ApplyNonRoundedIntersection(borderBox);
   }
   if (!borderBox.IsEmpty()) {
+    LayoutDeviceRect devPixelBorderBox =
+      LayoutDevicePixel::FromAppUnits(borderBox, aFrame->PresContext()->AppUnitsPerDevPixel());
+    LayoutDeviceRect transformedDevPixelBorderBox =
+      TransformTo<LayoutDevicePixel>(referenceFrameToRootReferenceFrame, devPixelBorderBox);
+    transformedDevPixelBorderBox.Round();
+    LayoutDeviceIntRect transformedDevPixelBorderBoxInt;
+    if (transformedDevPixelBorderBox.ToIntRect(&transformedDevPixelBorderBoxInt)) {
       const nsStyleUserInterface* styleUI = aFrame->StyleUserInterface();
       if (styleUI->mWindowDragging == NS_STYLE_WINDOW_DRAGGING_DRAG) {
-      mWindowDraggingRegion.OrWith(borderBox);
+        mWindowDraggingRegion.OrWith(LayoutDevicePixel::ToUntyped(transformedDevPixelBorderBoxInt));
       } else {
-      mWindowDraggingRegion.SubOut(borderBox);
+        mWindowDraggingRegion.SubOut(LayoutDevicePixel::ToUntyped(transformedDevPixelBorderBoxInt));
+      }
     }
   }
 }

layout/base/nsDisplayList.h

@@ -513,7 +513,7 @@ public:
    */
   void AdjustWindowDraggingRegion(nsIFrame* aFrame);
 
-  const nsRegion& GetWindowDraggingRegion() { return mWindowDraggingRegion; }
+  const nsIntRegion& GetWindowDraggingRegion() { return mWindowDraggingRegion; }
 
   /**
    * Allocate memory in our arena. It will only be freed when this display list
@@ -875,7 +875,7 @@ private:
   nsRect                         mDirtyRect;
   nsRegion                       mWindowExcludeGlassRegion;
   nsRegion                       mWindowOpaqueRegion;
-  nsRegion                       mWindowDraggingRegion;
+  nsIntRegion                    mWindowDraggingRegion;
   // The display item for the Windows window glass background, if any
   nsDisplayItem*                 mGlassDisplayItem;
   nsTArray<DisplayItemClip*>     mDisplayItemClipsToDestroy;

layout/base/nsLayoutUtils.cpp

@@ -3239,9 +3239,8 @@ nsLayoutUtils::PaintFrame(nsRenderingContext* aRenderingContext, nsIFrame* aFram
       widget->UpdateOpaqueRegion(
         opaqueRegion.ToNearestPixels(presContext->AppUnitsPerDevPixel()));
 
-      const nsRegion& draggingRegion = builder.GetWindowDraggingRegion();
-      widget->UpdateWindowDraggingRegion(
-        draggingRegion.ToNearestPixels(presContext->AppUnitsPerDevPixel()));
+      const nsIntRegion& draggingRegion = builder.GetWindowDraggingRegion();
+      widget->UpdateWindowDraggingRegion(draggingRegion);
     }
   }