Bug 1098417 part 1: Add optional anchor-point arg to nsLayoutUtils::ComputeObjectDestRect() and nsLayoutUtils::DrawSingleImage(). r=seth

layout/base/nsLayoutUtils.cpp

@@ -3628,7 +3628,8 @@ ComputeConcreteObjectSize(const nsSize& aConstraintSize,
 nsLayoutUtils::ComputeObjectDestRect(const nsRect& aConstraintRect,
                                      const IntrinsicSize& aIntrinsicSize,
                                      const nsSize& aIntrinsicRatio,
-                                     const nsStylePosition* aStylePos)
+                                     const nsStylePosition* aStylePos,
+                                     nsPoint* aAnchorPoint)
 {
   // Step 1: Figure out our "concrete object size"
   // (the size of the region we'll actually draw our image's pixels into).
@@ -3648,8 +3649,9 @@ nsLayoutUtils::ComputeObjectDestRect(const nsRect& aConstraintRect,
   imageTopLeftPt += aConstraintRect.TopLeft();
   imageAnchorPt += aConstraintRect.TopLeft();
 
-  // XXXdholbert Per bug 1098417, we should be returning imageAnchorPt here,
-  // and our caller should make sure it's pixel-aligned.
+  if (aAnchorPoint) {
+    *aAnchorPoint = imageAnchorPt;
+  }
   return nsRect(imageTopLeftPt, concreteObjectSize);
 }
 
@@ -5689,6 +5691,7 @@ nsLayoutUtils::DrawSingleImage(gfxContext&            aContext,
                                const nsRect&          aDirty,
                                const SVGImageContext* aSVGContext,
                                uint32_t               aImageFlags,
+                               const nsPoint*         aAnchorPoint,
                                const nsRect*          aSourceArea)
 {
   nscoord appUnitsPerCSSPixel = nsDeviceContext::AppUnitsPerCSSPixel();
@@ -5724,7 +5727,8 @@ nsLayoutUtils::DrawSingleImage(gfxContext&            aContext,
   nsRect fill;
   fill.IntersectRect(aDest, dest);
   return DrawImageInternal(aContext, aPresContext, image,
-                           aGraphicsFilter, dest, fill, fill.TopLeft(),
+                           aGraphicsFilter, dest, fill,
+                           aAnchorPoint ? *aAnchorPoint : fill.TopLeft(),
                            aDirty, aSVGContext, aImageFlags);
 }
 

layout/base/nsLayoutUtils.h

@@ -1149,13 +1149,17 @@ public:
    *                  example, a <video>'s poster-image has a dedicated
    *                  anonymous element & child-frame, but we should still use
    *                  the <video>'s 'object-fit' and 'object-position' values.)
+   * @param aAnchorPoint [out] A point that should be pixel-aligned by functions
+   *                           like nsLayoutUtils::DrawImage. See documentation
+   *                           in nsCSSRendering.h for ComputeObjectAnchorPoint.
    * @return The nsRect into which we should render the replaced content (using
    *         the same coordinate space as the passed-in aConstraintRect).
    */
   static nsRect ComputeObjectDestRect(const nsRect& aConstraintRect,
                                       const IntrinsicSize& aIntrinsicSize,
                                       const nsSize& aIntrinsicRatio,
-                                      const nsStylePosition* aStylePos);
+                                      const nsStylePosition* aStylePos,
+                                      nsPoint* aAnchorPoint = nullptr);
 
   /**
    * Get the font metrics corresponding to the frame's style data.
@@ -1677,6 +1681,8 @@ public:
    *                            raster images.
    *   @param aImageFlags       Image flags of the imgIContainer::FLAG_*
    *                            variety.
+   *   @param aAnchor           If non-null, a point which we will ensure
+   *                            is pixel-aligned in the output.
    *   @param aSourceArea       If non-null, this area is extracted from
    *                            the image and drawn in aDest. It's
    *                            in appunits. For best results it should
@@ -1690,6 +1696,7 @@ public:
                                   const nsRect&       aDirty,
                                   const mozilla::SVGImageContext* aSVGContext,
                                   uint32_t            aImageFlags,
+                                  const nsPoint*      aAnchorPoint = nullptr,
                                   const nsRect*       aSourceArea = nullptr);
 
   /**

layout/xul/nsImageBoxFrame.cpp

@@ -343,7 +343,8 @@ nsImageBoxFrame::PaintImage(nsRenderingContext& aRenderingContext,
     nsLayoutUtils::DrawSingleImage(*aRenderingContext.ThebesContext(),
         PresContext(), imgCon,
         nsLayoutUtils::GetGraphicsFilterForFrame(this),
-        rect, dirty, nullptr, aFlags, hasSubRect ? &mSubRect : nullptr);
+        rect, dirty, nullptr, aFlags, nullptr,
+        hasSubRect ? &mSubRect : nullptr);
   }
 }