Bug 1063224 - Add a PanStart() method to AsyncPanZoomController. r=kats

--HG--
extra : source : c26cacfcd1998dddd2982062c844e10bc5736541

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -1726,6 +1726,10 @@ float AsyncPanZoomController::PanDistance() const {
   return NS_hypot(mX.PanDistance(), mY.PanDistance());
 }
 
+ScreenPoint AsyncPanZoomController::PanStart() const {
+  return ScreenPoint(mX.PanStart(), mY.PanStart());
+}
+
 const ScreenPoint AsyncPanZoomController::GetVelocityVector() {
   return ScreenPoint(mX.GetVelocity(), mY.GetVelocity());
 }

gfx/layers/apz/src/AsyncPanZoomController.h

@@ -488,6 +488,16 @@ protected:
    */
   float PanDistance() const;
 
+  /**
+   * Gets the start point of the current touch.
+   * Like PanDistance(), this only makes sense if a touch is currently
+   * happening and OnTouchMove() or the equivalent for pan gestures is
+   * being invoked.
+   * Unlikely PanDistance(), this function returns a point in local screen
+   * coordinates.
+   */
+  ScreenPoint PanStart() const;
+
   /**
    * Gets a vector of the velocities of each axis.
    */

gfx/layers/apz/src/Axis.cpp

@@ -207,6 +207,10 @@ void Axis::ClearOverscroll() {
   mOverscroll = 0;
 }
 
+ScreenCoord Axis::PanStart() const {
+  return mStartPos;
+}
+
 ScreenCoord Axis::PanDistance() const {
   return fabs(mPos - mStartPos);
 }

gfx/layers/apz/src/Axis.h

@@ -118,16 +118,21 @@ public:
    */
   void ClearOverscroll();
 
+  /**
+   * Gets the starting position of the touch supplied in StartTouch().
+   */
+  ScreenCoord PanStart() const;
+
   /**
    * Gets the distance between the starting position of the touch supplied in
-   * startTouch() and the current touch from the last
-   * updateWithTouchAtDevicePoint().
+   * StartTouch() and the current touch from the last
+   * UpdateWithTouchAtDevicePoint().
    */
   ScreenCoord PanDistance() const;
 
   /**
    * Gets the distance between the starting position of the touch supplied in
-   * startTouch() and the supplied position.
+   * StartTouch() and the supplied position.
    */
   ScreenCoord PanDistance(ScreenCoord aPos) const;