Bug 732016 Allow override of the scroll port size used for clamping scroll positions. r=roc

dom/base/nsDOMWindowUtils.cpp

@@ -2317,3 +2317,26 @@ nsDOMWindowUtils::GetPlugins(JSContext* cx, jsval* aPlugins)
   *aPlugins = OBJECT_TO_JSVAL(jsPlugins);
   return NS_OK;
 }
+
+NS_IMETHODIMP
+nsDOMWindowUtils::SetScrollPositionClampingScrollPortSize(float aWidth, float aHeight)
+{
+  if (!IsUniversalXPConnectCapable()) {
+    return NS_ERROR_DOM_SECURITY_ERR;
+  }
+
+  if (!(aWidth >= 0.0 && aHeight >= 0.0)) {
+    return NS_ERROR_ILLEGAL_VALUE;
+  }
+
+  nsIPresShell* presShell = GetPresShell();
+  if (!presShell) {
+    return NS_ERROR_FAILURE;
+  }
+
+  presShell->SetScrollPositionClampingScrollPortSize(
+    nsPresContext::CSSPixelsToAppUnits(aWidth),
+    nsPresContext::CSSPixelsToAppUnits(aHeight));
+
+  return NS_OK;
+}

dom/interfaces/base/nsIDOMWindowUtils.idl

@@ -70,7 +70,7 @@ interface nsIDOMFile;
 interface nsIFile;
 interface nsIDOMTouch;
 
-[scriptable, uuid(c7f303a1-4f7b-4d38-a192-c3f0e25dadb1)]
+[scriptable, uuid(66a68858-df38-40e1-a792-fda04ebcc084)]
 interface nsIDOMWindowUtils : nsISupports {
 
   /**
@@ -1110,4 +1110,12 @@ interface nsIDOMWindowUtils : nsISupports {
    */
   [implicit_jscontext]
   readonly attribute jsval plugins;
+
+  /**
+   * Set the scrollport size for the purposes of clamping scroll positions for
+   * the root scroll frame of this document to be (aWidth,aHeight) in CSS pixels.
+   *
+   * The caller of this method must have UniversalXPConnect privileges.
+   */
+  void setScrollPositionClampingScrollPortSize(in float aWidth, in float aHeight);
 };

layout/base/nsIPresShell.h

@@ -1265,6 +1265,15 @@ public:
   // clears that capture.
   static void ClearMouseCapture(nsIFrame* aFrame);
 
+  void SetScrollPositionClampingScrollPortSize(nscoord aWidth, nscoord aHeight);
+  bool IsScrollPositionClampingScrollPortSizeSet() {
+    return mScrollPositionClampingScrollPortSizeSet;
+  }
+  nsSize GetScrollPositionClampingScrollPortSize() {
+    NS_ASSERTION(mScrollPositionClampingScrollPortSizeSet, "asking for scroll port when its not set?");
+    return mScrollPositionClampingScrollPortSize;
+  }
+
 protected:
   friend class nsRefreshDriver;
 
@@ -1315,6 +1324,8 @@ protected:
 
   bool                      mSuppressInterruptibleReflows;
 
+  bool                      mScrollPositionClampingScrollPortSizeSet;
+
   // A list of weak frames. This is a pointer to the last item in the list.
   nsWeakFrame*              mWeakFrames;
 
@@ -1333,6 +1344,8 @@ protected:
   float                     mXResolution;
   float                     mYResolution;
 
+  nsSize                    mScrollPositionClampingScrollPortSize;
+
   static nsIContent* gKeyDownTarget;
 };
 

layout/base/nsPresShell.cpp

@@ -831,6 +831,8 @@ PresShell::PresShell()
   mYResolution = 1.0;
   mViewportOverridden = false;
 
+  mScrollPositionClampingScrollPortSizeSet = false;
+
   static bool addedSynthMouseMove = false;
   if (!addedSynthMouseMove) {
     Preferences::AddBoolVarCache(&sSynthMouseMove,
@@ -9147,3 +9149,10 @@ PresShell::SizeOfTextRuns(nsMallocSizeOfFun aMallocSizeOf) const
                                                 /* clear = */false);
 }
 
+void
+nsIPresShell::SetScrollPositionClampingScrollPortSize(nscoord aWidth, nscoord aHeight)
+{
+  mScrollPositionClampingScrollPortSizeSet = true;
+  mScrollPositionClampingScrollPortSize.width = aWidth;
+  mScrollPositionClampingScrollPortSize.height = aHeight;
+}

layout/generic/nsGfxScrollFrame.cpp

@@ -1645,7 +1645,7 @@ Clamp(nscoord aLower, nscoord aVal, nscoord aUpper)
 nsPoint
 nsGfxScrollFrameInner::ClampScrollPosition(const nsPoint& aPt) const
 {
-  nsRect range = GetScrollRange();
+  nsRect range = GetScrollRangeForClamping();
   return nsPoint(Clamp(range.x, aPt.x, range.XMost()),
                  Clamp(range.y, aPt.y, range.YMost()));
 }
@@ -1971,7 +1971,7 @@ nsGfxScrollFrameInner::RestrictToDevPixels(const nsPoint& aPt,
   // pixels. But we also need to make sure that our position remains
   // inside the allowed region.
   if (aShouldClamp) {
-    nsRect scrollRange = GetScrollRange();
+    nsRect scrollRange = GetScrollRangeForClamping();
     *aPtDevPx = nsIntPoint(ClampInt(scrollRange.x, aPt.x, scrollRange.XMost(), appUnitsPerDevPixel),
                            ClampInt(scrollRange.y, aPt.y, scrollRange.YMost(), appUnitsPerDevPixel));
   } else {
@@ -2326,10 +2326,16 @@ AlignToDevPixelRoundingToZero(nscoord aVal, PRInt32 aAppUnitsPerDevPixel)
 
 nsRect
 nsGfxScrollFrameInner::GetScrollRange() const
+{
+  return GetScrollRange(mScrollPort.width, mScrollPort.height);
+}
+
+nsRect
+nsGfxScrollFrameInner::GetScrollRange(nscoord aWidth, nscoord aHeight) const
 {
   nsRect range = GetScrolledRect();
-  range.width -= mScrollPort.width;
-  range.height -= mScrollPort.height;
+  range.width -= aWidth;
+  range.height -= aHeight;
 
   nsPresContext* presContext = mOuter->PresContext();
   PRInt32 appUnitsPerDevPixel = presContext->AppUnitsPerDevPixel();
@@ -2342,6 +2348,17 @@ nsGfxScrollFrameInner::GetScrollRange() const
   return range;
 }
 
+nsRect
+nsGfxScrollFrameInner::GetScrollRangeForClamping() const
+{
+  nsIPresShell* presShell = mOuter->PresContext()->PresShell();
+  if (mIsRoot && presShell->IsScrollPositionClampingScrollPortSizeSet()) {
+    nsSize size = presShell->GetScrollPositionClampingScrollPortSize();
+    return GetScrollRange(size.width, size.height);
+  }
+  return GetScrollRange();
+}
+
 static void
 AdjustForWholeDelta(PRInt32 aDelta, nscoord* aCoord)
 {

layout/generic/nsGfxScrollFrame.h

@@ -178,7 +178,12 @@ public:
     return pt;
   }
   nsRect GetScrollRange() const;
+  // Get the scroll range assuming the scrollport has size (aWidth, aHeight).
+  nsRect GetScrollRange(nscoord aWidth, nscoord aHeight) const;
+protected:
+  nsRect GetScrollRangeForClamping() const;
 
+public:
   nsPoint RestrictToDevPixels(const nsPoint& aPt, nsIntPoint* aPtDevPx, bool aShouldClamp) const;
   nsPoint ClampScrollPosition(const nsPoint& aPt) const;
   static void AsyncScrollCallback(nsITimer *aTimer, void* anInstance);