Clamp APZ wheel event deltas to the size of a page scroll. (bug 1146676, r=kats)

gfx/ipc/GfxMessageUtils.h

@@ -752,6 +752,7 @@ struct ParamTraits<mozilla::layers::FrameMetrics>
     WriteParam(aMsg, aParam.mDoSmoothScroll);
     WriteParam(aMsg, aParam.mSmoothScrollOffset);
     WriteParam(aMsg, aParam.GetLineScrollAmount());
+    WriteParam(aMsg, aParam.GetPageScrollAmount());
     WriteParam(aMsg, aParam.AllowVerticalScrollWithWheel());
     WriteParam(aMsg, aParam.GetContentDescription());
   }
@@ -793,6 +794,7 @@ struct ParamTraits<mozilla::layers::FrameMetrics>
             ReadParam(aMsg, aIter, &aResult->mDoSmoothScroll) &&
             ReadParam(aMsg, aIter, &aResult->mSmoothScrollOffset) &&
             ReadParam(aMsg, aIter, &aResult->mLineScrollAmount) &&
+            ReadParam(aMsg, aIter, &aResult->mPageScrollAmount) &&
             ReadParam(aMsg, aIter, &aResult->mAllowVerticalScrollWithWheel) &&
             ReadContentDescription(aMsg, aIter, aResult));
   }

gfx/layers/FrameMetrics.h

@@ -64,6 +64,7 @@ public:
     , mExtraResolution()
     , mBackgroundColor(0, 0, 0, 0)
     , mLineScrollAmount(0, 0)
+    , mPageScrollAmount(0, 0)
     , mAllowVerticalScrollWithWheel(false)
   {
   }
@@ -96,6 +97,7 @@ public:
            mBackgroundColor == aOther.mBackgroundColor &&
            mDoSmoothScroll == aOther.mDoSmoothScroll &&
            mLineScrollAmount == aOther.mLineScrollAmount &&
+           mPageScrollAmount == aOther.mPageScrollAmount &&
            mAllowVerticalScrollWithWheel == aOther.mAllowVerticalScrollWithWheel;
   }
   bool operator!=(const FrameMetrics& aOther) const
@@ -496,6 +498,16 @@ public:
     mLineScrollAmount = size;
   }
 
+  const LayoutDeviceIntSize& GetPageScrollAmount() const
+  {
+    return mPageScrollAmount;
+  }
+
+  void SetPageScrollAmount(const LayoutDeviceIntSize& size)
+  {
+    mPageScrollAmount = size;
+  }
+
   const CSSRect& GetScrollableRect() const
   {
     return mScrollableRect;
@@ -664,6 +676,9 @@ private:
   // The value of GetLineScrollAmount(), for scroll frames.
   LayoutDeviceIntSize mLineScrollAmount;
 
+  // The value of GetPageScrollAmount(), for scroll frames.
+  LayoutDeviceIntSize mPageScrollAmount;
+
   // Whether or not the frame can be vertically scrolled with a mouse wheel.
   bool mAllowVerticalScrollWithWheel;
 };

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -1441,6 +1441,18 @@ AsyncPanZoomController::GetScrollWheelDelta(const ScrollWheelInput& aEvent,
     default:
       MOZ_ASSERT_UNREACHABLE("unexpected scroll delta type");
   }
+
+  LayoutDeviceIntSize pageScrollSize = mFrameMetrics.GetPageScrollAmount();
+  if (Abs(aOutDeltaX) > pageScrollSize.width) {
+    aOutDeltaX = (aOutDeltaX >= 0)
+                 ? pageScrollSize.width
+                 : -pageScrollSize.width;
+  }
+  if (Abs(aOutDeltaY) > pageScrollSize.height) {
+    aOutDeltaY = (aOutDeltaY >= 0)
+                 ? pageScrollSize.height
+                 : -pageScrollSize.height;
+  }
 }
 
 // Return whether or not the underlying layer can be scrolled on either axis.

layout/base/nsDisplayList.cpp

@@ -795,6 +795,11 @@ nsDisplayScrollLayer::ComputeFrameMetrics(nsIFrame* aForFrame,
       LayoutDeviceIntSize::FromAppUnitsRounded(lineScrollAmount, presContext->AppUnitsPerDevPixel());
     metrics.SetLineScrollAmount(lineScrollAmountInDevPixels);
 
+    nsSize pageScrollAmount = scrollableFrame->GetPageScrollAmount();
+    LayoutDeviceIntSize pageScrollAmountInDevPixels =
+      LayoutDeviceIntSize::FromAppUnitsRounded(pageScrollAmount, presContext->AppUnitsPerDevPixel());
+    metrics.SetPageScrollAmount(pageScrollAmountInDevPixels);
+
     if (!aScrollFrame->GetParent() ||
         EventStateManager::CanVerticallyScrollFrameWithWheel(aScrollFrame->GetParent()))
     {