phase based wheel scroll latching for mac

content/browser/renderer_host/render_widget_host_view_mac.mm

 // Copyright (c) 2012 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/render_widget_host_view_mac.h"
 
 #import <Carbon/Carbon.h>
 #import <objc/runtime.h>
 #include <OpenGL/gl.h>
 #include <QuartzCore/QuartzCore.h>
@@ skipping 1737 matching lines @@
 
   if (changed_metrics & DisplayObserver::DISPLAY_METRIC_DEVICE_SCALE_FACTOR) {
     RenderWidgetHostImpl* host =
         RenderWidgetHostImpl::From(GetRenderWidgetHost());
     if (host && host->delegate())
       host->delegate()->UpdateDeviceScaleFactor(display.device_scale_factor());
   }
 
   UpdateScreenInfo(cocoa_view_);
 }
+void RenderWidgetHostViewMac::SendSyntheticWheelEventWithPhaseEnded(
+    blink::WebMouseWheelEvent wheel_event,
+    bool should_route_event) {
+  wheel_event.dispatch_type =
+      blink::WebInputEvent::DispatchType::kEventNonBlocking;
+  if (should_route_event) {
+    render_widget_host_->delegate()
+        ->GetInputEventRouter()
+        ->RouteMouseWheelEvent(this, &wheel_event,
+                               ui::LatencyInfo(ui::SourceEventType::WHEEL));
+  } else {
+    ProcessMouseWheelEvent(wheel_event,
+                           ui::LatencyInfo(ui::SourceEventType::WHEEL));
+  }
+}
+
+void RenderWidgetHostViewMac::StartMouseWheelEndDispatchTimer(
+    blink::WebMouseWheelEvent wheel_event,
+    bool should_route_event) {
+  mouse_wheel_end_dispatch_timer_.Start(
+      FROM_HERE,
+      base::TimeDelta::FromMilliseconds(
+          kDefaultMouseWheelLatchingTransactionMs),
+      base::Bind(
+          &RenderWidgetHostViewMac::SendSyntheticWheelEventWithPhaseEnded,
+          base::Unretained(this), wheel_event, should_route_event));
+}
 
 }  // namespace content
 
 // RenderWidgetHostViewCocoa ---------------------------------------------------
 
 @implementation RenderWidgetHostViewCocoa
 @synthesize selectedRange = selectedRange_;
 @synthesize suppressNextEscapeKeyUp = suppressNextEscapeKeyUp_;
 @synthesize markedRange = markedRange_;
 
@@ skipping 581 matching lines @@
   if ([event phase] != NSEventPhaseEnded &&
       [event phase] != NSEventPhaseCancelled) {
     return;
   }
 
   if (renderWidgetHostView_->render_widget_host_) {
     // History-swiping is not possible if the logic reaches this point.
     WebMouseWheelEvent webEvent = WebMouseWheelEventBuilder::Build(
         event, self);
     webEvent.rails_mode = mouseWheelFilter_.UpdateRailsMode(webEvent);
-    ui::LatencyInfo latency_info(ui::SourceEventType::WHEEL);
-    latency_info.AddLatencyNumber(ui::INPUT_EVENT_LATENCY_UI_COMPONENT, 0, 0);
-    renderWidgetHostView_->render_widget_host_->
-        ForwardWheelEventWithLatencyInfo(webEvent, latency_info);
+    if (renderWidgetHostView_->WheelScrollLatchingEnabled()) {
+      renderWidgetHostView_->StartMouseWheelEndDispatchTimer(webEvent, false);
+    } else {
+      ui::LatencyInfo latency_info(ui::SourceEventType::WHEEL);
+      latency_info.AddLatencyNumber(ui::INPUT_EVENT_LATENCY_UI_COMPONENT, 0, 0);
+      renderWidgetHostView_->render_widget_host_
+          ->ForwardWheelEventWithLatencyInfo(webEvent, latency_info);
+    }
   }
 
   if (endWheelMonitor_) {
     [NSEvent removeMonitor:endWheelMonitor_];
     endWheelMonitor_ = nil;
   }
 }
 
 - (void)beginGestureWithEvent:(NSEvent*)event {
   [responderDelegate_ beginGestureWithEvent:event];
@@ skipping 185 matching lines @@
           return blockEvent;
       }];
   }
 
   // This is responsible for content scrolling!
   if (renderWidgetHostView_->render_widget_host_) {
     WebMouseWheelEvent webEvent = WebMouseWheelEventBuilder::Build(event, self);
     webEvent.rails_mode = mouseWheelFilter_.UpdateRailsMode(webEvent);
     ui::LatencyInfo latency_info(ui::SourceEventType::WHEEL);
     latency_info.AddLatencyNumber(ui::INPUT_EVENT_LATENCY_UI_COMPONENT, 0, 0);
+    if (renderWidgetHostView_->WheelScrollLatchingEnabled()) {
+      if (webEvent.phase == blink::WebMouseWheelEvent::kPhaseEnded) {

[tdresser, 2017/05/25 15:18:36]

Could you add a comment per condition here?

[sahel, 2017/05/25 16:00:04]

Done.

+        renderWidgetHostView_->StartMouseWheelEndDispatchTimer(
+            webEvent, renderWidgetHostView_->ShouldRouteEvent(webEvent));
+        return;
+      }
+      if (webEvent.phase == blink::WebMouseWheelEvent::kPhaseBegan) {
+        // A new scrolling sequence hase started, stop the timer and send its

[tdresser, 2017/05/25 15:18:36]

hase -> has

[sahel, 2017/05/25 16:00:04]

Done.

+        // wheel end event.
+        if (renderWidgetHostView_->mouse_wheel_end_dispatch_timer_
+                .IsRunning()) {
+          base::Closure task =
+              renderWidgetHostView_->mouse_wheel_end_dispatch_timer_
+                  .user_task();
+          renderWidgetHostView_->mouse_wheel_end_dispatch_timer_.Stop();
+          task.Run();
+        }
+
+      } else if (webEvent.momentum_phase ==
+                 blink::WebMouseWheelEvent::kPhaseBegan) {
+        renderWidgetHostView_->mouse_wheel_end_dispatch_timer_.Stop();
+      }
+    }
+
     if (renderWidgetHostView_->ShouldRouteEvent(webEvent)) {
       renderWidgetHostView_->render_widget_host_->delegate()
           ->GetInputEventRouter()
           ->RouteMouseWheelEvent(renderWidgetHostView_.get(), &webEvent,
                                  latency_info);
     } else {
       renderWidgetHostView_->ProcessMouseWheelEvent(webEvent, latency_info);
     }
   }
 }
@@ skipping 946 matching lines @@
 
 // "-webkit-app-region: drag | no-drag" is implemented on Mac by excluding
 // regions that are not draggable. (See ControlRegionView in
 // native_app_window_cocoa.mm). This requires the render host view to be
 // draggable by default.
 - (BOOL)mouseDownCanMoveWindow {
   return YES;
 }
 
 @end