Bug 1193062 - Process pan gesture deltas in begin+end events. r=kats

We don't want to split native NSEvents into two PanGestureInput events.

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -1673,6 +1673,9 @@ nsEventStatus AsyncPanZoomController::OnPanBegin(const PanGestureInput& aEvent)
     SetState(PANNING);
   }
 
+  // Call into OnPan in order to process any delta included in this event.
+  OnPan(aEvent, true);
+
   return nsEventStatus_eConsumeNoDefault;
 }
 
@@ -1680,17 +1683,29 @@ nsEventStatus AsyncPanZoomController::OnPan(const PanGestureInput& aEvent, bool
   APZC_LOG("%p got a pan-pan in state %d\n", this, mState);
 
   if (mState == SMOOTH_SCROLL) {
-    if (aEvent.mType == PanGestureInput::PANGESTURE_MOMENTUMPAN) {
+    if (!aFingersOnTouchpad) {
       // When a SMOOTH_SCROLL scroll is being processed on a frame, mouse
       // wheel and trackpad momentum scroll position updates will not cancel the
       // SMOOTH_SCROLL scroll animations, enabling scripts that depend on
       // them to be responsive without forcing the user to wait for the momentum
       // scrolling to completely stop.
       return nsEventStatus_eConsumeNoDefault;
-    } else {
+    }
+
     // SMOOTH_SCROLL scrolls are cancelled by pan gestures.
     CancelAnimation();
   }
+
+  if (mState == NOTHING) {
+    // This event block was interrupted by something else. If the user's fingers
+    // are still on on the touchpad we want to resume scrolling, otherwise we
+    // ignore the rest of the scroll gesture.
+    if (!aFingersOnTouchpad) {
+      return nsEventStatus_eConsumeNoDefault;
+    }
+    // Resume / restart the pan.
+    // PanBegin will call back into this function with mState == PANNING.
+    return OnPanBegin(aEvent);
   }
 
   // We need to update the axis velocity in order to get a useful display port
@@ -1717,6 +1732,9 @@ nsEventStatus AsyncPanZoomController::OnPan(const PanGestureInput& aEvent, bool
 nsEventStatus AsyncPanZoomController::OnPanEnd(const PanGestureInput& aEvent) {
   APZC_LOG("%p got a pan-end in state %d\n", this, mState);
 
+  // Call into OnPan in order to process any delta included in this event.
+  OnPan(aEvent, true);
+
   mX.EndTouch(aEvent.mTime);
   mY.EndTouch(aEvent.mTime);
   SetState(NOTHING);
@@ -1735,12 +1753,17 @@ nsEventStatus AsyncPanZoomController::OnPanMomentumStart(const PanGestureInput&
 
   SetState(PAN_MOMENTUM);
 
+  // Call into OnPan in order to process any delta included in this event.
+  OnPan(aEvent, false);
+
   return nsEventStatus_eConsumeNoDefault;
 }
 
 nsEventStatus AsyncPanZoomController::OnPanMomentumEnd(const PanGestureInput& aEvent) {
   APZC_LOG("%p got a pan-momentumend in state %d\n", this, mState);
 
+  // Call into OnPan in order to process any delta included in this event.
+  OnPan(aEvent, false);
 
   // We need to reset the velocity to zero. We don't really have a "touch"
   // here because the touch has already ended long before the momentum

widget/InputData.h

@@ -322,7 +322,7 @@ public:
   PanGestureType mType;
   ScreenPoint mPanStartPoint;
 
-  // Only non-zero if mType is PANGESTURE_PAN or PANGESTURE_MOMENTUMPAN.
+  // The delta. This can be non-zero on any type of event.
   ScreenPoint mPanDisplacement;
 
   // Versions of |mPanStartPoint| and |mPanDisplacement| in the local