GestureScrollEnd event had non-zero velocity causing overscroll on software fling path.

ui/base/gestures/gesture_sequence.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 "ui/base/gestures/gesture_sequence.h"
 
 #include <cmath>
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 464 matching lines @@
                                              float x_velocity,
                                              float y_velocity) {
   float railed_x_velocity = x_velocity;
   float railed_y_velocity = y_velocity;
 
   if (scroll_type_ == ST_HORIZONTAL)
     railed_y_velocity = 0;
   else if (scroll_type_ == ST_VERTICAL)
     railed_x_velocity = 0;
 
+  // TODO(rjkroege): It is conceivable that we could suppress sending the
+  // GestureScrollEnd if it is immediately followed by a GestureFlingStart.
   gestures->push_back(helper_->CreateGestureEvent(
       ui::ET_GESTURE_SCROLL_END,
       location,
       flags_,
       base::Time::FromDoubleT(point.last_touch_time()),
-      railed_x_velocity, railed_y_velocity, 1 << point.touch_id()));
+      0., 0., 1 << point.touch_id()));
 
   if (railed_x_velocity != 0 || railed_y_velocity != 0) {
     // TODO(sad|rjkroege): fling-curve is currently configured to work well with
     // touchpad scroll-events. This curve needs to be adjusted to work correctly
-    // with both touchpad and touchscreen. Until then, multiply the velocity for
-    // touchscreen with a constant.
+    // with both touchpad and touchscreen. Until then, scale quadratically.
     // http://crbug.com/120154
+    float velocity_scaling  = 1. / 900.;

[sadrul, 2012/05/31 15:19:23]

const?

[rjkroege, 2012/05/31 15:26:46]

done

+
     gestures->push_back(helper_->CreateGestureEvent(
         ui::ET_SCROLL_FLING_START,
         location,
         flags_,
         base::Time::FromDoubleT(point.last_touch_time()),
-        railed_x_velocity * 2.5, railed_y_velocity * 2.5,
+        velocity_scaling * railed_x_velocity * fabsf(railed_x_velocity),
+        velocity_scaling * railed_y_velocity * fabsf(railed_y_velocity),
         1 << point.touch_id()));
   }
 }
 
 void GestureSequence::AppendScrollGestureUpdate(const GesturePoint& point,
                                                 const gfx::Point& location,
                                                 Gestures* gestures) {
   int dx = location.x() - bounding_box_last_center_.x();
   int dy = location.y() - bounding_box_last_center_.y();
   if (dx == 0 && dy == 0)
@@ skipping 272 matching lines @@
     sign_y = 0;
   else
     sign_x = 0;
 
   AppendSwipeGesture(point, sign_x, sign_y, gestures);
 
   return true;
 }
 
 }  // namespace ui