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 19 matching lines @@
  private:
   bool original_can_scroll_;
   DISALLOW_COPY_AND_ASSIGN(QueuedWebMouseWheelEvent);
 };
 
 MouseWheelEventQueue::MouseWheelEventQueue(MouseWheelEventQueueClient* client,
                                            bool send_gestures,
                                            int64_t scroll_transaction_ms)
     : client_(client),
       needs_scroll_begin_(true),
+      needs_scroll_end_(false),
       send_gestures_(send_gestures),
       scroll_transaction_ms_(scroll_transaction_ms),
       scrolling_device_(blink::WebGestureDeviceUninitialized) {
   DCHECK(client);
 }
 
 MouseWheelEventQueue::~MouseWheelEventQueue() {
   if (!wheel_queue_.empty())
     STLDeleteElements(&wheel_queue_);
 }
@@ skipping 28 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 =
+        event_sent_for_gesture_ack_->event.timeStampSeconds;
+
     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;
+    // Only OSX populates the momentumPhase; so expect this to
+    // always be PhaseNone on all other platforms.
+    scroll_update.event.data.scrollUpdate.inertial =
+        event_sent_for_gesture_ack_->event.momentumPhase !=
+        blink::WebMouseWheelEvent::PhaseNone;
     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 has_phase_info = false;
+
+    if (event_sent_for_gesture_ack_->event.phase !=
+            blink::WebMouseWheelEvent::PhaseNone ||
+        event_sent_for_gesture_ack_->event.momentumPhase !=
+            blink::WebMouseWheelEvent::PhaseNone) {
+      has_phase_info = true;
+      send_end_now = event_sent_for_gesture_ack_->event.phase ==

[tdresser, 2016/03/08 14:28:52]

Add a comment describing the conditions in which we should send an end.

[dtapuska, 2016/03/08 20:31:49]

I'm hoping the renaming of the variable makes it clear that a comment isn't
needed. Let me know if you still feel it does.

+                         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;
+    }
+
+    bool needs_update = scroll_update.event.data.scrollUpdate.deltaX != 0 ||
+                        scroll_update.event.data.scrollUpdate.deltaY != 0;
+
+    if (needs_update || !(needs_scroll_begin_ && send_end_now)) {

[tdresser, 2016/03/08 14:28:52]

I'm a bit confused by this condition.

It's probably a bit easier to read as:
if (needs_update || !needs_scroll_begin || !send_end_now)

I'm not quite clear on why this it's necessary though. Maybe add a comment?

[dtapuska, 2016/03/08 20:31:49]

Done.

+      if (needs_scroll_begin_ || has_phase_info)
+        SendScrollBegin(scroll_update, !needs_scroll_begin_);

[tdresser, 2016/03/08 14:28:52]

This is a bit confusing. Why do we mark it synthetic if we don't need a scroll
begin?

[dtapuska, 2016/03/08 20:31:49]

I've broken it apart to make it more clear.

+
+      if (needs_update)
+        client_->SendGestureEvent(scroll_update);
+
+      if (send_end_now) {

[tdresser, 2016/03/08 14:28:52]

The naming of this variable is confusing. We send a scroll end even if
send_end_now is false?

[dtapuska, 2016/03/08 20:31:49]

I've changed send_end_now to current_phase_ended...

+        SendScrollEnd(scroll_update.event, false);
+      } else if (has_phase_info) {
+        SendScrollEnd(scroll_update.event, true);
+      } else {
+        scroll_end_timer_.Start(
+            FROM_HERE,
+            base::TimeDelta::FromMilliseconds(scroll_transaction_ms_),
+            base::Bind(&MouseWheelEventQueue::SendScrollEnd,
+                       base::Unretained(this), scroll_update.event, false));
+      }
+    }
   }
 
   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 23 matching lines @@
   event_sent_for_gesture_ack_.reset(wheel_queue_.front());
   wheel_queue_.pop_front();
 
   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;
+void MouseWheelEventQueue::SendScrollEnd(blink::WebGestureEvent update_event,
+                                         bool synthetic) {
+  DCHECK((synthetic && !needs_scroll_end_) || needs_scroll_end_);
+
+  GestureEventWithLatencyInfo scroll_end(update_event);
+  scroll_end.event.timeStampSeconds =
+      (base::TimeTicks::Now() - base::TimeTicks()).InSecondsF();
   scroll_end.event.type = WebInputEvent::GestureScrollEnd;
-  scroll_end.event.sourceDevice = blink::WebGestureDeviceTouchpad;
   scroll_end.event.resendingPluginId = -1;
+  scroll_end.event.data.scrollEnd.synthetic = synthetic;
+  scroll_end.event.data.scrollEnd.inertial =
+      update_event.data.scrollUpdate.inertial;
   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);
+  if (!synthetic) {
+    needs_scroll_begin_ = true;
+    needs_scroll_end_ = false;
+
+    if (scroll_end_timer_.IsRunning())
+      scroll_end_timer_.Reset();
+  }
+  client_->SendGestureEvent(scroll_end);
 }
 
-void MouseWheelEventQueue::SendGesture(
-    const GestureEventWithLatencyInfo& gesture) {
-  switch (gesture.event.type) {
-    case WebInputEvent::GestureScrollUpdate:
-      if (needs_scroll_begin_) {
-        GestureEventWithLatencyInfo scroll_begin(gesture);
-        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.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;
+void MouseWheelEventQueue::SendScrollBegin(
+    const GestureEventWithLatencyInfo& gesture_update,
+    bool synthetic) {
+  DCHECK((synthetic && !needs_scroll_begin_) || needs_scroll_begin_);
 
-        SendGesture(scroll_begin);
-      }
-      if (scroll_end_timer_.IsRunning()) {
-        scroll_end_timer_.Reset();
-      } else {
-        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);
+  GestureEventWithLatencyInfo scroll_begin(gesture_update);
+  scroll_begin.event.type = WebInputEvent::GestureScrollBegin;
+  scroll_begin.event.data.scrollBegin.synthetic = synthetic;
+  scroll_begin.event.data.scrollBegin.inertial =
+      gesture_update.event.data.scrollUpdate.inertial;
+  scroll_begin.event.data.scrollBegin.deltaXHint =
+      gesture_update.event.data.scrollUpdate.deltaX;
+  scroll_begin.event.data.scrollBegin.deltaYHint =
+      gesture_update.event.data.scrollUpdate.deltaY;
+  scroll_begin.event.data.scrollBegin.targetViewport = false;
+  scroll_begin.event.data.scrollBegin.deltaHintUnits =
+      gesture_update.event.data.scrollUpdate.deltaUnits;
+
+  needs_scroll_begin_ = false;
+  needs_scroll_end_ = true;
+  client_->SendGestureEvent(scroll_begin);
 }
 
 }  // namespace content