Setting Accurate ScrollResult from Blink for Elastic Scroll.

content/renderer/render_widget.cc

 // 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/renderer/render_widget.h"
 
 #include "base/auto_reset.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/logging.h"
@@ skipping 2197 matching lines @@
       UpdateTextInputState(SHOW_IME_IF_NEEDED, FROM_NON_IME);
   }
 #endif
 }
 
 void RenderWidget::didOverscroll(
     const blink::WebFloatSize& unusedDelta,
     const blink::WebFloatSize& accumulatedRootOverScroll,
     const blink::WebFloatPoint& position,
     const blink::WebFloatSize& velocity) {
+  if (compositor_deps_->IsElasticOverscrollEnabled()) {
+    latest_overscroll_delta_ =
+        gfx::Vector2dF(-unusedDelta.width, -unusedDelta.height);
+    return;
+  }
+
   DidOverscrollParams params;
   // TODO(jdduke): Consider bundling the overscroll with the input event ack to
   // save an IPC.
   params.accumulated_overscroll = gfx::Vector2dF(
       accumulatedRootOverScroll.width, accumulatedRootOverScroll.height);
   params.latest_overscroll_delta =
       gfx::Vector2dF(unusedDelta.width, unusedDelta.height);
   // TODO(sataya.m): don't negate velocity once http://crbug.com/499743 is
   // fixed.
   params.current_fling_velocity =
@@ skipping 58 matching lines @@
 void RenderWidget::ObserveWheelEventAndResult(
     const blink::WebMouseWheelEvent& wheel_event,
     bool event_processed) {
   if (!compositor_deps_->IsElasticOverscrollEnabled())
     return;
 
   // Blink does not accurately compute scroll bubbling or overscroll. For now,
   // assume that an unprocessed event was entirely an overscroll, and that a
   // processed event was entirely scroll.
   // TODO(ccameron): Retrieve an accurate scroll result from Blink.
   // http://crbug.com/442859

[ccameron, 2015/06/23 16:09:16]

Even if event_processed is true, if you have a latest_overscroll_delta_ you
should still process that. So something like

scroll_result.did_scroll = event_processed;
scroll_result.did_overscroll_result = !latest_overscroll_delta_.isZero();
scroll_result.unused_scroll_delta = latest_overscroll_delta_;

or something to that effect.

   cc::InputHandlerScrollResult scroll_result;
   if (event_processed) {
     scroll_result.did_scroll = true;
   } else {
     scroll_result.did_overscroll_root = true;
-    scroll_result.unused_scroll_delta =
-        gfx::Vector2dF(-wheel_event.deltaX, -wheel_event.deltaY);
+    scroll_result.unused_scroll_delta = latest_overscroll_delta_;
+    latest_overscroll_delta_.set_x(0);
+    latest_overscroll_delta_.set_y(0);
   }
 
   RenderThreadImpl* render_thread = RenderThreadImpl::current();
   InputHandlerManager* input_handler_manager =
       render_thread ? render_thread->input_handler_manager() : NULL;
   if (input_handler_manager) {
     input_handler_manager->ObserveWheelEventAndResultOnMainThread(
         routing_id_, wheel_event, scroll_result);
   }
 }
@@ skipping 136 matching lines @@
 void RenderWidget::RegisterVideoHoleFrame(RenderFrameImpl* frame) {
   video_hole_frames_.AddObserver(frame);
 }
 
 void RenderWidget::UnregisterVideoHoleFrame(RenderFrameImpl* frame) {
   video_hole_frames_.RemoveObserver(frame);
 }
 #endif  // defined(VIDEO_HOLE)
 
 }  // namespace content