From e6453f4c35edbb8dbde638984b74d1d7f6c4ecf2 Mon Sep 17 00:00:00 2001
From: Markus Stange <mstange@themasta.com>
Date: Mon, 28 Mar 2016 14:56:28 -0400
Subject: [PATCH] Bug 1254275 - Inspect the event queue to find out whether
 momentum events are following. r=kats a=ritu

MozReview-Commit-ID: 6k3SaJ6X7Mr
---
 gfx/layers/apz/src/AsyncPanZoomController.cpp |  4 ++++
 widget/InputData.h                            |  5 +++++
 widget/cocoa/nsChildView.mm                   | 14 ++++++++++++++
 3 files changed, 23 insertions(+)

diff --git a/gfx/layers/apz/src/AsyncPanZoomController.cpp b/gfx/layers/apz/src/AsyncPanZoomController.cpp
index 3b62337fc40..0b6cbe45c02 100644
--- a/gfx/layers/apz/src/AsyncPanZoomController.cpp
+++ b/gfx/layers/apz/src/AsyncPanZoomController.cpp
@@ -1992,6 +1992,10 @@ nsEventStatus AsyncPanZoomController::OnPanEnd(const PanGestureInput& aEvent) {
   SetState(NOTHING);
   RequestContentRepaint();
 
+  if (!aEvent.mFollowedByMomentum) {
+    RequestSnap();
+  }
+
   return nsEventStatus_eConsumeNoDefault;
 }
 
diff --git a/widget/InputData.h b/widget/InputData.h
index 304fbd539df..a96f155897f 100644
--- a/widget/InputData.h
+++ b/widget/InputData.h
@@ -358,6 +358,7 @@ public:
       mLineOrPageDeltaX(0),
       mLineOrPageDeltaY(0),
       mHandledByAPZ(false),
+      mFollowedByMomentum(false),
       mRequiresContentResponseIfCannotScrollHorizontallyInStartDirection(false)
   {
   }
@@ -385,6 +386,10 @@ public:
 
   bool mHandledByAPZ;
 
+  // true if this is a PANGESTURE_END event that will be followed by a
+  // PANGESTURE_MOMENTUMSTART event.
+  bool mFollowedByMomentum;
+
   // If this is true, and this event started a new input block that couldn't
   // find a scrollable target which is scrollable in the horizontal component
   // of the scroll start direction, then this input block needs to be put on
diff --git a/widget/cocoa/nsChildView.mm b/widget/cocoa/nsChildView.mm
index 2f7795ef51d..e003c3cbf9e 100644
--- a/widget/cocoa/nsChildView.mm
+++ b/widget/cocoa/nsChildView.mm
@@ -4963,6 +4963,20 @@ PanGestureTypeForEvent(NSEvent* aEvent)
     panEvent.mLineOrPageDeltaX = lineOrPageDeltaX;
     panEvent.mLineOrPageDeltaY = lineOrPageDeltaY;
 
+    if (panEvent.mType == PanGestureInput::PANGESTURE_END) {
+      // Check if there's a momentum start event in the event queue, so that we
+      // can annotate this event.
+      NSEvent* nextWheelEvent =
+        [NSApp nextEventMatchingMask:NSScrollWheelMask
+                           untilDate:[NSDate distantPast]
+                              inMode:NSDefaultRunLoopMode
+                             dequeue:NO];
+      if (nextWheelEvent &&
+          PanGestureTypeForEvent(nextWheelEvent) == PanGestureInput::PANGESTURE_MOMENTUMSTART) {
+        panEvent.mFollowedByMomentum = true;
+      }
+    }
+
     bool canTriggerSwipe = [self shouldConsiderStartingSwipeFromEvent:theEvent];
     panEvent.mRequiresContentResponseIfCannotScrollHorizontallyInStartDirection = canTriggerSwipe;
     mGeckoChild->DispatchAPZWheelInputEvent(panEvent, canTriggerSwipe);