Bug 1255634 - APZ should scroll by more than a page with large values of mousewheel.default.delta_multiplier_{x,y}. r=masayuki,kats

The constants in doTestWholeScroll() have to be reduced because
otherwise some subtests end up returning results that are off by a few
pixels with e10s, presumably due to differences in floating point
precision in APZ compared to non-APZ.

MozReview-Commit-ID: BxmqHrcN8IL

dom/events/EventStateManager.h

@@ -294,6 +294,15 @@ public:
   static nsWeakPtr sPointerLockedElement;
   static nsWeakPtr sPointerLockedDoc;
 
+  /**
+   * If the absolute values of mMultiplierX and/or mMultiplierY are equal or
+   * larger than this value, the computed scroll amount isn't rounded down to
+   * the page width or height.
+   */
+  enum {
+    MIN_MULTIPLIER_VALUE_ALLOWING_OVER_ONE_PAGE_SCROLL = 1000
+  };
+
 protected:
   /**
    * Prefs class capsules preference management.
@@ -560,15 +569,6 @@ protected:
 
     void Reset();
 
-    /**
-     * If the abosolute values of mMultiplierX and/or mMultiplierY are equals or
-     * larger than this value, the computed scroll amount isn't rounded down to
-     * the page width or height.
-     */
-    enum {
-      MIN_MULTIPLIER_VALUE_ALLOWING_OVER_ONE_PAGE_SCROLL = 1000
-    };
-
     bool mInit[COUNT_OF_MULTIPLIERS];
     double mMultiplierX[COUNT_OF_MULTIPLIERS];
     double mMultiplierY[COUNT_OF_MULTIPLIERS];

dom/events/test/window_wheel_default_action.html

@@ -1352,8 +1352,8 @@ function doTestZoomedScroll(aCallback)
 function doTestWholeScroll(aCallback)
 {
   SpecialPowers.pushPrefEnv({"set": [
-    ["mousewheel.default.delta_multiplier_x", 99999999],
-    ["mousewheel.default.delta_multiplier_y", 99999999]]},
+    ["mousewheel.default.delta_multiplier_x", 999999],
+    ["mousewheel.default.delta_multiplier_y", 999999]]},
     function() { doTestWholeScroll2(aCallback); });
 }
 

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -1650,6 +1650,14 @@ AsyncPanZoomController::ConvertToGecko(const ScreenIntPoint& aPoint, CSSPoint* a
   return false;
 }
 
+static bool
+AllowsScrollingMoreThanOnePage(double aMultiplier)
+{
+  const int32_t kMinAllowPageScroll =
+    EventStateManager::MIN_MULTIPLIER_VALUE_ALLOWING_OVER_ONE_PAGE_SCROLL;
+  return Abs(aMultiplier) >= kMinAllowPageScroll;
+}
+
 ParentLayerPoint
 AsyncPanZoomController::GetScrollWheelDelta(const ScrollWheelInput& aEvent) const
 {
@@ -1720,12 +1728,16 @@ AsyncPanZoomController::GetScrollWheelDelta(const ScrollWheelInput& aEvent) cons
     }
   }
 
-  if (Abs(delta.x) > pageScrollSize.width) {
+  // We shouldn't scroll more than one page at once except when the
+  // user preference is large.
+  if (!AllowsScrollingMoreThanOnePage(aEvent.mUserDeltaMultiplierX) &&
+      Abs(delta.x) > pageScrollSize.width) {
     delta.x = (delta.x >= 0)
               ? pageScrollSize.width
               : -pageScrollSize.width;
   }
-  if (Abs(delta.y) > pageScrollSize.height) {
+  if (!AllowsScrollingMoreThanOnePage(aEvent.mUserDeltaMultiplierY) &&
+      Abs(delta.y) > pageScrollSize.height) {
     delta.y = (delta.y >= 0)
               ? pageScrollSize.height
               : -pageScrollSize.height;