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 2129 matching lines @@
   // We assume that the absence of synchronous_compositor_factory
   // means we are in Chrome. In chrome, we want to clip, i.e.
   // *not* to record the full layer.
   if (!synchronous_compositor_factory)
     return false;
 
   return synchronous_compositor_factory->RecordFullLayer();
 }
 #endif
 
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+bool RenderWidget::IsElasticOverscrollEnabled() const {
+  return compositor_deps_->IsElasticOverscrollEnabled();
+}
+#endif
+
 bool RenderWidget::CanComposeInline() {
   return true;
 }
 
 WebScreenInfo RenderWidget::screenInfo() {
   return screen_info_;
 }
 
 float RenderWidget::deviceScaleFactor() {
   return device_scale_factor_;
@@ skipping 48 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()) {
+    unused_delta_on_wheel_overscroll_ =
+        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 51 matching lines @@
 }
 
 bool RenderWidget::WillHandleGestureEvent(
     const blink::WebGestureEvent& event) {
   return false;
 }
 
 void RenderWidget::ObserveWheelEventAndResult(
     const blink::WebMouseWheelEvent& wheel_event,
     bool event_processed) {
   if (!compositor_deps_->IsElasticOverscrollEnabled())

[jdduke (slow), 2015/06/25 23:55:45]

With https://codereview.chromium.org/1209043002/, you should be able to pass a
DidOverscrollParams* (optional) value into this function using
|event_overscroll.get()|. Then you can populate the scroll results depending on
those values.

     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
   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.did_scroll = event_processed;
+  scroll_result.did_overscroll_root =
+      !unused_delta_on_wheel_overscroll_.IsZero();
+  scroll_result.unused_scroll_delta = unused_delta_on_wheel_overscroll_;
+  unused_delta_on_wheel_overscroll_.set_x(0);
+  unused_delta_on_wheel_overscroll_.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 135 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