Impl thread smooth scrolling.

content/renderer/input/input_handler_proxy.cc

 // Copyright 2013 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/renderer/input/input_handler_proxy.h"
 
 #include "base/auto_reset.h"
+#include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "content/common/input/did_overscroll_params.h"
 #include "content/common/input/web_input_event_traits.h"
+#include "content/public/common/content_switches.h"
 #include "content/renderer/input/input_handler_proxy_client.h"
 #include "third_party/WebKit/public/platform/Platform.h"
 #include "third_party/WebKit/public/web/WebInputEvent.h"
 #include "ui/events/latency_info.h"
 #include "ui/gfx/frame_time.h"
 #include "ui/gfx/geometry/point_conversions.h"
 
 using blink::WebFloatPoint;
 using blink::WebFloatSize;
 using blink::WebGestureEvent;
@@ skipping 127 matching lines @@
       expect_scroll_update_end_(false),
 #endif
       gesture_scroll_on_impl_thread_(false),
       gesture_pinch_on_impl_thread_(false),
       fling_may_be_active_on_main_thread_(false),
       disallow_horizontal_fling_scroll_(false),
       disallow_vertical_fling_scroll_(false),
       has_fling_animation_started_(false) {
   DCHECK(client);
   input_handler_->BindToClient(this);
+  smooth_scroll_enabled_ = CommandLine::ForCurrentProcess()->HasSwitch(

[jdduke (slow), 2014/07/08 21:26:20]

Apologies for the drive-by, but why do we need a flag here? Don't we want this
behavior on all platforms that support impl thread event handling (Android
included)?

[jdduke (slow), 2014/07/08 21:28:34]

Hmm, disregard that, it looks like you're re-using an existing flag (although
I'm curious why smooth scrolling isn't enabled by default?).

+      switches::kEnableSmoothScrolling);
 }
 
 InputHandlerProxy::~InputHandlerProxy() {}
 
 void InputHandlerProxy::WillShutdown() {
   input_handler_ = NULL;
   client_->WillShutdown();
 }
 
 InputHandlerProxy::EventDisposition
@@ skipping 31 matching lines @@
     if (wheel_event.scrollByPage) {
       // TODO(jamesr): We don't properly handle scroll by page in the compositor
       // thread, so punt it to the main thread. http://crbug.com/236639
       return DID_NOT_HANDLE;
     }
     if (wheel_event.modifiers & WebInputEvent::ControlKey) {
       // Wheel events involving the control key never trigger scrolling, only
       // event handlers.  Forward to the main thread.
       return DID_NOT_HANDLE;
     }
+    if (smooth_scroll_enabled_) {
+      cc::InputHandler::ScrollStatus scroll_status =
+          input_handler_->ScrollAnimated(
+              gfx::Point(wheel_event.x, wheel_event.y),
+              gfx::Vector2dF(-wheel_event.deltaX, -wheel_event.deltaY));
+      switch (scroll_status) {
+        case cc::InputHandler::ScrollStarted:
+          return DID_HANDLE;
+        case cc::InputHandler::ScrollIgnored:
+          return DROP_EVENT;
+        default:
+          return DID_NOT_HANDLE;
+      }
+    }
     cc::InputHandler::ScrollStatus scroll_status = input_handler_->ScrollBegin(
         gfx::Point(wheel_event.x, wheel_event.y), cc::InputHandler::Wheel);
     switch (scroll_status) {
       case cc::InputHandler::ScrollStarted: {
         TRACE_EVENT_INSTANT2(
             "input",
             "InputHandlerProxy::handle_input wheel scroll",
             TRACE_EVENT_SCOPE_THREAD,
             "deltaX",
             -wheel_event.deltaX,
@@ skipping 564 matching lines @@
   // trigger a scroll, e.g., with a trivial time delta between fling updates.
   // Return true in this case to prevent early fling termination.
   if (std::abs(clipped_increment.width) < kScrollEpsilon &&
       std::abs(clipped_increment.height) < kScrollEpsilon)
     return true;
 
   return did_scroll;
 }
 
 }  // namespace content