Implement Wheel Gesture Scrolling on OSX.

content/browser/renderer_host/input/mouse_wheel_event_queue.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/input/mouse_wheel_event_queue.h"
 
 #include "base/metrics/histogram_macros.h"
 #include "base/stl_util.h"
 #include "base/trace_event/trace_event.h"
 
@@ skipping 67 matching lines @@
 
   event_sent_for_gesture_ack_->latency.AddNewLatencyFrom(latency_info);
   client_->OnMouseWheelEventAck(*event_sent_for_gesture_ack_, ack_result);
 
   // If event wasn't consumed then generate a gesture scroll for it.
   if (send_gestures_ && ack_result != INPUT_EVENT_ACK_STATE_CONSUMED &&
       event_sent_for_gesture_ack_->event.canScroll &&
       (scrolling_device_ == blink::WebGestureDeviceUninitialized ||
        scrolling_device_ == blink::WebGestureDeviceTouchpad)) {
     GestureEventWithLatencyInfo scroll_update;
+    scroll_update.event.timeStampSeconds =
+        (base::TimeTicks::Now() - base::TimeTicks()).InSecondsF();

[tdresser, 2016/03/02 18:26:53]

We should take the timestamp from the wheel event. (We use the touch event
timestamps for gesture events).

[dtapuska, 2016/03/07 18:03:59]

Done.

+
     scroll_update.event.x = event_sent_for_gesture_ack_->event.x;
     scroll_update.event.y = event_sent_for_gesture_ack_->event.y;
     scroll_update.event.globalX = event_sent_for_gesture_ack_->event.globalX;
     scroll_update.event.globalY = event_sent_for_gesture_ack_->event.globalY;
     scroll_update.event.type = WebInputEvent::GestureScrollUpdate;
     scroll_update.event.sourceDevice = blink::WebGestureDeviceTouchpad;
     scroll_update.event.resendingPluginId = -1;
     scroll_update.event.data.scrollUpdate.deltaX =
         event_sent_for_gesture_ack_->event.deltaX;
     scroll_update.event.data.scrollUpdate.deltaY =
         event_sent_for_gesture_ack_->event.deltaY;
+    scroll_update.event.data.scrollUpdate.inertial =
+        event_sent_for_gesture_ack_->event.momentumPhase !=
+        blink::WebMouseWheelEvent::PhaseNone;

[tdresser, 2016/03/02 18:26:53]

What's the momentum phase for non-mac?
Maybe add a comment?

[dtapuska, 2016/03/07 18:03:59]

Done.

     if (event_sent_for_gesture_ack_->event.scrollByPage) {
       scroll_update.event.data.scrollUpdate.deltaUnits =
           blink::WebGestureEvent::Page;
 
       // Turn page scrolls into a *single* page scroll because
       // the magnitude the number of ticks is lost when coalescing.
       if (scroll_update.event.data.scrollUpdate.deltaX)
         scroll_update.event.data.scrollUpdate.deltaX =
             scroll_update.event.data.scrollUpdate.deltaX > 0 ? 1 : -1;
       if (scroll_update.event.data.scrollUpdate.deltaY)
         scroll_update.event.data.scrollUpdate.deltaY =
             scroll_update.event.data.scrollUpdate.deltaY > 0 ? 1 : -1;
     } else {
       scroll_update.event.data.scrollUpdate.deltaUnits =
           event_sent_for_gesture_ack_->event.hasPreciseScrollingDeltas
               ? blink::WebGestureEvent::PrecisePixels
               : blink::WebGestureEvent::Pixels;
     }
-    SendGesture(scroll_update);
+
+    bool send_end_now = false;
+    bool schedule_end = true;
+
+    if (event_sent_for_gesture_ack_->event.phase !=
+            blink::WebMouseWheelEvent::PhaseNone ||
+        event_sent_for_gesture_ack_->event.momentumPhase !=
+            blink::WebMouseWheelEvent::PhaseNone) {
+      schedule_end = false;
+      send_end_now = event_sent_for_gesture_ack_->event.phase ==
+                         blink::WebMouseWheelEvent::PhaseEnded ||
+                     event_sent_for_gesture_ack_->event.phase ==
+                         blink::WebMouseWheelEvent::PhaseCancelled ||
+                     event_sent_for_gesture_ack_->event.momentumPhase ==
+                         blink::WebMouseWheelEvent::PhaseEnded ||
+                     event_sent_for_gesture_ack_->event.momentumPhase ==
+                         blink::WebMouseWheelEvent::PhaseCancelled;
+    }
+
+    if (scroll_update.event.data.scrollUpdate.deltaX != 0 ||
+        scroll_update.event.data.scrollUpdate.deltaY != 0)
+      SendGesture(scroll_update, schedule_end);
+    if (send_end_now)
+      SendScrollEnd(scroll_update.event);
   }
 
   event_sent_for_gesture_ack_.reset();
   TryForwardNextEventToRenderer();
 }
 
 void MouseWheelEventQueue::OnGestureScrollEvent(
     const GestureEventWithLatencyInfo& gesture_event) {
   if (gesture_event.event.type == blink::WebInputEvent::GestureScrollBegin) {
     // If there is a current scroll going on and a new scroll that isn't
@@ skipping 25 matching lines @@
 
   MouseWheelEventWithLatencyInfo send_event(*event_sent_for_gesture_ack_);
   if (send_gestures_)
     send_event.event.canScroll = false;
 
   client_->SendMouseWheelEventImmediately(send_event);
 }
 
 void MouseWheelEventQueue::SendScrollEnd(blink::WebGestureEvent update_event) {
   GestureEventWithLatencyInfo scroll_end;
+  scroll_end.event.timeStampSeconds =
+      (base::TimeTicks::Now() - base::TimeTicks()).InSecondsF();

[tdresser, 2016/03/02 18:26:53]

I suppose this timestamp needs to be made up, unfortunately.

[dtapuska, 2016/03/07 18:03:59]

Acknowledged.

   scroll_end.event.type = WebInputEvent::GestureScrollEnd;
   scroll_end.event.sourceDevice = blink::WebGestureDeviceTouchpad;
   scroll_end.event.resendingPluginId = -1;
   scroll_end.event.data.scrollEnd.deltaUnits =
       update_event.data.scrollUpdate.deltaUnits;
   scroll_end.event.x = update_event.x;
   scroll_end.event.y = update_event.y;
   scroll_end.event.globalX = update_event.globalX;
   scroll_end.event.globalY = update_event.globalY;
 
-  SendGesture(scroll_end);
+  SendGesture(scroll_end, false);
 }
 
 void MouseWheelEventQueue::SendGesture(
-    const GestureEventWithLatencyInfo& gesture) {
+    const GestureEventWithLatencyInfo& gesture,
+    bool generate_end) {
   switch (gesture.event.type) {
     case WebInputEvent::GestureScrollUpdate:
       if (needs_scroll_begin_) {
         GestureEventWithLatencyInfo scroll_begin(gesture);
+        scroll_begin.event.timeStampSeconds = gesture.event.timeStampSeconds;
         scroll_begin.event.x = gesture.event.x;
         scroll_begin.event.y = gesture.event.y;
         scroll_begin.event.globalX = gesture.event.globalX;
         scroll_begin.event.globalY = gesture.event.globalY;
         scroll_begin.event.type = WebInputEvent::GestureScrollBegin;
+        scroll_begin.event.data.scrollBegin.inertial =
+            gesture.event.data.scrollUpdate.inertial;

[tdresser, 2016/03/02 18:26:53]

It isn't clear to me when we'd need a scroll begin but have an inertial update.

When will this happen?

[dtapuska, 2016/03/07 18:03:59]

So the way phasing is done on OSX is that the phase terminates and it doesn't
transition into the inertial state via a GSU... ie; it will be:
GSB (inertial = false)
GSU (inertial = false)
GSE 
GSB (inertial = true)
GSU (inertial = true)
GSE

If we wanted to avoid the GSE/GSB in the middle we could hold onto generating
the GSE not based on when the phases change but based on a timer. However I have
seen events not generate a momentum phase and just terminate. So in those cases
the GSE would be delayed by the timer. This seemed to be the best compromise;
and it was similar to the events requested in here:
https://github.com/w3c/uievents/issues/58

         scroll_begin.event.data.scrollBegin.deltaXHint =
             gesture.event.data.scrollUpdate.deltaX;
         scroll_begin.event.data.scrollBegin.deltaYHint =
             gesture.event.data.scrollUpdate.deltaY;
         scroll_begin.event.data.scrollBegin.targetViewport = false;
         scroll_begin.event.data.scrollBegin.deltaHintUnits =
             gesture.event.data.scrollUpdate.deltaUnits;
 
-        SendGesture(scroll_begin);
+        SendGesture(scroll_begin, false);
       }
-      if (scroll_end_timer_.IsRunning()) {
+      if (scroll_end_timer_.IsRunning())
         scroll_end_timer_.Reset();
-      } else {
+
+      if (generate_end) {
         scroll_end_timer_.Start(
             FROM_HERE,
             base::TimeDelta::FromMilliseconds(scroll_transaction_ms_),
             base::Bind(&MouseWheelEventQueue::SendScrollEnd,
                        base::Unretained(this), gesture.event));
       }
       break;
     case WebInputEvent::GestureScrollEnd:
       needs_scroll_begin_ = true;
       break;
     case WebInputEvent::GestureScrollBegin:
       needs_scroll_begin_ = false;
       break;
     default:
       return;
   }
   client_->SendGestureEvent(gesture);
 }
 
 }  // namespace content