beginSmoothScroll should send wheel ticks at constant velocity.

content/browser/renderer_host/render_widget_host_view_base.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/render_widget_host_view_base.h"
 
 #include "base/logging.h"
 #include "content/browser/accessibility/browser_accessibility_manager.h"
 #include "content/browser/renderer_host/render_widget_host_impl.h"
 #include "content/port/browser/smooth_scroll_gesture.h"
@@ skipping 24 matching lines @@
 #endif
 
 namespace content {
 
 // How long a smooth scroll gesture should run when it is a near scroll.
 static const int64 kDurationOfNearScrollGestureMs = 150;
 
 // How long a smooth scroll gesture should run when it is a far scroll.
 static const int64 kDurationOfFarScrollGestureMs = 500;
 
+static const int64 kWheelTicksPerSecond = 1500;
+
 // static
 RenderWidgetHostViewPort* RenderWidgetHostViewPort::FromRWHV(
     RenderWidgetHostView* rwhv) {
   return static_cast<RenderWidgetHostViewPort*>(rwhv);
 }
 
 // static
 RenderWidgetHostViewPort* RenderWidgetHostViewPort::CreateViewForWidget(
     content::RenderWidgetHost* widget) {
   return FromRWHV(RenderWidgetHostView::CreateViewForWidget(widget));
@@ skipping 356 matching lines @@
     impl->NotifyScreenInfoChanged();
   }
 }
 
 class BasicMouseWheelSmoothScrollGesture
     : public SmoothScrollGesture {
  public:
   BasicMouseWheelSmoothScrollGesture(bool scroll_down, bool scroll_far,
                                      int mouse_event_x, int mouse_event_y)
       : start_time_(base::TimeTicks::HighResNow()),
+        last_forward_time_(start_time_),
         scroll_down_(scroll_down),
         scroll_far_(scroll_far),
         mouse_event_x_(mouse_event_x),
         mouse_event_y_(mouse_event_y) { }
 
   virtual bool ForwardInputEvents(base::TimeTicks now,
                                   RenderWidgetHost* host) OVERRIDE {
     int64 duration_in_ms;
     if (scroll_far_)
       duration_in_ms = kDurationOfFarScrollGestureMs;
     else
       duration_in_ms = kDurationOfNearScrollGestureMs;
 
     if (now - start_time_ > base::TimeDelta::FromMilliseconds(duration_in_ms))
       return false;
 
+    // Figure out how many wheel ticks to send.
+    double seconds_since_last_tick = (now - last_forward_time_).InSecondsF();
+    int num_wheel_ticks = static_cast<int>(
+        seconds_since_last_tick * kWheelTicksPerSecond);
+    if (!num_wheel_ticks) {
+      TRACE_EVENT_INSTANT1("input", "NoMovement",
+                           "seconds_since_last_tick", seconds_since_last_tick);
+      return true;
+    }
+
+    last_forward_time_ = now;
+
     WebKit::WebMouseWheelEvent event;
     event.type = WebKit::WebInputEvent::MouseWheel;
     // TODO(nduca): Figure out plausible value.
     event.deltaY = scroll_down_ ? -10 : 10;
-    event.wheelTicksY = scroll_down_ ? 1 : -1;
+    event.wheelTicksY = (scroll_down_ ? 1 : -1) * num_wheel_ticks;
     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);
     return true;
   }
 
  private:
   virtual ~BasicMouseWheelSmoothScrollGesture() { }
   base::TimeTicks start_time_;
+  base::TimeTicks last_forward_time_;
   bool scroll_down_;
   bool scroll_far_;
   int mouse_event_x_;
   int mouse_event_y_;
 };
 
 SmoothScrollGesture* RenderWidgetHostViewBase::CreateSmoothScrollGesture(
     bool scroll_down, bool scroll_far, int mouse_event_x, int mouse_event_y) {
   return new BasicMouseWheelSmoothScrollGesture(scroll_down, scroll_far,
                                                 mouse_event_x, mouse_event_y);
 }
 
 }  // namespace content