Attempt to linearize the scroll deltas created in RenderWidgetHostViewBase

content/browser/renderer_host/basic_mouse_wheel_smooth_scroll_gesture.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/browser/renderer_host/basic_mouse_wheel_smooth_scroll_gesture.h"
+
+#include "base/debug/trace_event.h"
+#include "content/browser/renderer_host/render_widget_host_impl.h"
+
+namespace content {
+
+BasicMouseWheelSmoothScrollGesture::BasicMouseWheelSmoothScrollGesture(
+    bool scroll_down, int pixels_to_scroll,
+    int mouse_event_x, int mouse_event_y)
+    : scroll_down_(scroll_down),
+      pixels_scrolled_(0),
+      pixels_to_scroll_(pixels_to_scroll),
+      mouse_event_x_(mouse_event_x),
+      mouse_event_y_(mouse_event_y) { }
+
+BasicMouseWheelSmoothScrollGesture::~BasicMouseWheelSmoothScrollGesture() { }
+
+bool BasicMouseWheelSmoothScrollGesture::ForwardInputEvents(
+    base::TimeTicks now, RenderWidgetHost* host) {
+
+  if (pixels_scrolled_ >= pixels_to_scroll_)
+    return false;
+
+  double positionDelta = 10;
+  if (!last_tick_time_.is_null()) {
+    RenderWidgetHostImpl* hostImpl = RenderWidgetHostImpl::From(host);
+    double desiredIntervalMs = hostImpl->SyntheticScrollMessageInterval();
+    double velocity = 10 / desiredIntervalMs;
+    double timeDelta = (now - last_tick_time_).InMillisecondsF();
+    positionDelta = velocity * timeDelta;
+  }
+
+  last_tick_time_ = now;
+
+  WebKit::WebMouseWheelEvent event;
+  event.type = WebKit::WebInputEvent::MouseWheel;
+  event.hasPreciseScrollingDeltas = 1;
+  event.deltaY = scroll_down_ ? -positionDelta : positionDelta;
+  // TODO(vollick): find a proper way to access
+  // WebCore::WheelEvent::tickMultiplier.
+  event.wheelTicksY = event.deltaY / 120;
+  event.modifiers = 0;
+
+  // TODO(nduca): Figure out plausible x and y values.
+  event.globalX = 0;
+  event.globalY = 0;
+  event.x = mouse_event_x_;
+  event.y = mouse_event_y_;
+  event.windowX = event.x;
+  event.windowY = event.y;
+  host->ForwardWheelEvent(event);
+
+  pixels_scrolled_ += abs(event.deltaY);
+
+  TRACE_COUNTER_ID1(
+      "gpu", "smooth_scroll_by_pixels_scrolled", this, pixels_scrolled_);
+
+  return true;
+}
+
+}  // content
+