Bug 383026. Centralize code that converts DOM scroll offsets to/from layout scroll positions. r=dbaron

--HG--
extra : rebase_source : a6118e0eeea749a601e055741e35cdcd15d81e57

content/base/src/nsGenericElement.cpp

@@ -607,10 +607,7 @@ PRInt32
 nsGenericElement::GetScrollTop()
 {
   nsIScrollableFrame* sf = GetScrollFrame();
-
-  return sf ?
-         nsPresContext::AppUnitsToIntCSSPixels(sf->GetScrollPosition().y) :
-         0;
+  return sf ? sf->GetScrollPositionCSSPixels().y : 0;
 }
 
 NS_IMETHODIMP
@@ -626,9 +623,7 @@ nsGenericElement::SetScrollTop(PRInt32 aScrollTop)
 {
   nsIScrollableFrame* sf = GetScrollFrame();
   if (sf) {
-    nsPoint pt = sf->GetScrollPosition();
-    sf->ScrollToCSSPixels(nsIntPoint(nsPresContext::AppUnitsToIntCSSPixels(pt.x),
-                                     aScrollTop));
+    sf->ScrollToCSSPixels(nsIntPoint(sf->GetScrollPositionCSSPixels().x, aScrollTop));
   }
   return NS_OK;
 }
@@ -637,10 +632,7 @@ PRInt32
 nsGenericElement::GetScrollLeft()
 {
   nsIScrollableFrame* sf = GetScrollFrame();
-
-  return sf ?
-         nsPresContext::AppUnitsToIntCSSPixels(sf->GetScrollPosition().x) :
-         0;
+  return sf ? sf->GetScrollPositionCSSPixels().x : 0;
 }
 
 NS_IMETHODIMP
@@ -656,9 +648,7 @@ nsGenericElement::SetScrollLeft(PRInt32 aScrollLeft)
 {
   nsIScrollableFrame* sf = GetScrollFrame();
   if (sf) {
-    nsPoint pt = sf->GetScrollPosition();
-    sf->ScrollToCSSPixels(nsIntPoint(aScrollLeft,
-                                     nsPresContext::AppUnitsToIntCSSPixels(pt.y)));
+    sf->ScrollToCSSPixels(nsIntPoint(aScrollLeft, sf->GetScrollPositionCSSPixels().y));
   }
   return NS_OK;
 }

dom/base/nsGlobalWindow.cpp

@@ -4322,11 +4322,13 @@ nsGlobalWindow::GetScrollXY(PRInt32* aScrollX, PRInt32* aScrollY,
     return GetScrollXY(aScrollX, aScrollY, true);
   }
 
-  if (aScrollX)
-    *aScrollX = nsPresContext::AppUnitsToIntCSSPixels(scrollPos.x);
-  if (aScrollY)
-    *aScrollY = nsPresContext::AppUnitsToIntCSSPixels(scrollPos.y);
-
+  nsIntPoint scrollPosCSSPixels = sf->GetScrollPositionCSSPixels();
+  if (aScrollX) {
+    *aScrollX = scrollPosCSSPixels.x;
+  }
+  if (aScrollY) {
+    *aScrollY = scrollPosCSSPixels.y;
+  }
   return NS_OK;
 }
 

layout/generic/nsGfxScrollFrame.cpp

@@ -1683,18 +1683,19 @@ void
 nsGfxScrollFrameInner::ScrollToCSSPixels(nsIntPoint aScrollPosition)
 {
   nsPoint current = GetScrollPosition();
+  nsIntPoint currentCSSPixels = GetScrollPositionCSSPixels();
   nsPoint pt(nsPresContext::CSSPixelsToAppUnits(aScrollPosition.x),
              nsPresContext::CSSPixelsToAppUnits(aScrollPosition.y));
   nscoord halfPixel = nsPresContext::CSSPixelsToAppUnits(0.5f);
   nsRect range(pt.x - halfPixel, pt.y - halfPixel, 2*halfPixel - 1, 2*halfPixel - 1);
-  if (nsPresContext::AppUnitsToIntCSSPixels(current.x) == aScrollPosition.x) {
+  if (currentCSSPixels.x == aScrollPosition.x) {
     pt.x = current.x;
     range.x = pt.x;
     range.width = 0;
   } else {
     // current.x must be outside 'range', so we must move in the correct direction.
   }
-  if (nsPresContext::AppUnitsToIntCSSPixels(current.y) == aScrollPosition.y) {
+  if (currentCSSPixels.y == aScrollPosition.y) {
     pt.y = current.y;
     range.y = pt.y;
     range.height = 0;
@@ -1704,6 +1705,14 @@ nsGfxScrollFrameInner::ScrollToCSSPixels(nsIntPoint aScrollPosition)
   ScrollTo(pt, nsIScrollableFrame::INSTANT, &range);
 }
 
+nsIntPoint
+nsGfxScrollFrameInner::GetScrollPositionCSSPixels()
+{
+  nsPoint pt = GetScrollPosition();
+  return nsIntPoint(nsPresContext::AppUnitsToIntCSSPixels(pt.x),
+                    nsPresContext::AppUnitsToIntCSSPixels(pt.y));
+}
+
 /*
  * this method wraps calls to ScrollToImpl(), either in one shot or incrementally,
  *  based on the setting of the smoothness scroll pref

layout/generic/nsGfxScrollFrame.h

@@ -166,6 +166,7 @@ public:
     ScrollToWithOrigin(aScrollPosition, aMode, nsGkAtoms::other, aRange);
   }
   void ScrollToCSSPixels(nsIntPoint aScrollPosition);
+  nsIntPoint GetScrollPositionCSSPixels();
   void ScrollToImpl(nsPoint aScrollPosition, const nsRect& aRange);
   void ScrollVisual(nsPoint aOldScrolledFramePosition);
   void ScrollBy(nsIntPoint aDelta, nsIScrollableFrame::ScrollUnit aUnit,
@@ -480,6 +481,9 @@ public:
   virtual void ScrollToCSSPixels(nsIntPoint aScrollPosition) {
     mInner.ScrollToCSSPixels(aScrollPosition);
   }
+  virtual nsIntPoint GetScrollPositionCSSPixels() {
+    return mInner.GetScrollPositionCSSPixels();
+  }
   virtual void ScrollBy(nsIntPoint aDelta, ScrollUnit aUnit, ScrollMode aMode,
                         nsIntPoint* aOverflow, nsIAtom *aOrigin = nullptr) {
     mInner.ScrollBy(aDelta, aUnit, aMode, aOverflow, aOrigin);
@@ -725,6 +729,9 @@ public:
   virtual void ScrollToCSSPixels(nsIntPoint aScrollPosition) {
     mInner.ScrollToCSSPixels(aScrollPosition);
   }
+  virtual nsIntPoint GetScrollPositionCSSPixels() {
+    return mInner.GetScrollPositionCSSPixels();
+  }
   virtual void ScrollBy(nsIntPoint aDelta, ScrollUnit aUnit, ScrollMode aMode,
                         nsIntPoint* aOverflow, nsIAtom *aOrigin = nullptr) {
     mInner.ScrollBy(aDelta, aUnit, aMode, aOverflow, aOrigin);

layout/generic/nsIScrollableFrame.h

@@ -138,6 +138,11 @@ public:
    * The scroll mode is INSTANT.
    */
   virtual void ScrollToCSSPixels(nsIntPoint aScrollPosition) = 0;
+  /**
+   * Returns the scroll position in integer CSS pixels, rounded to the nearest
+   * pixel.
+   */
+  virtual nsIntPoint GetScrollPositionCSSPixels() = 0;
   /**
    * When scrolling by a relative amount, we can choose various units.
    */

layout/xul/base/src/nsScrollBoxObject.cpp

@@ -263,9 +263,9 @@ NS_IMETHODIMP nsScrollBoxObject::GetPosition(PRInt32 *x, PRInt32 *y)
   if (!sf)
      return NS_ERROR_FAILURE;
 
-  nsPoint pt = sf->GetScrollPosition();
-  *x = nsPresContext::AppUnitsToIntCSSPixels(pt.x);
-  *y = nsPresContext::AppUnitsToIntCSSPixels(pt.y);
+  nsIntPoint pt = sf->GetScrollPositionCSSPixels();
+  *x = pt.x;
+  *y = pt.y;
 
   return NS_OK;  
 }