gesture recognizer: Make sure the pinch/scroll only when the finger is moved for real.

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 657 matching lines @@
         1 << point.touch_id()));
   }
 }
 
 void GestureSequence::AppendScrollGestureUpdate(const GesturePoint& point,
                                                 const gfx::Point& location,
                                                 Gestures* gestures) {
   gfx::Point current_center = bounding_box_.CenterPoint();
   int dx = current_center.x() - bounding_box_last_center_.x();
   int dy = current_center.y() - bounding_box_last_center_.y();
-  if (dx == 0 && dy == 0)
-    return;
   if (scroll_type_ == ST_HORIZONTAL)
     dy = 0;
   else if (scroll_type_ == ST_VERTICAL)
     dx = 0;
+  if (dx == 0 && dy == 0)
+    return;
 
   gestures->push_back(CreateGestureEvent(
       GestureEventDetails(ui::ET_GESTURE_SCROLL_UPDATE, dx, dy),
       location,
       flags_,
       base::Time::FromDoubleT(point.last_touch_time()),
       ComputeTouchBitmask(points_)));
 }
 
 void GestureSequence::AppendPinchGestureBegin(const GesturePoint& p1,
@@ skipping 207 matching lines @@
     AppendScrollGestureBegin(point, center, gestures);
   }
 
   return true;
 }
 
 bool GestureSequence::PinchUpdate(const TouchEvent& event,
     const GesturePoint& point, Gestures* gestures) {
   DCHECK(state_ == GS_PINCH);
 
+  // It is possible that the none of the touch-points changed their position,
+  // but their radii changed, and that caused the bounding box to also change.
+  // But in such cases, we do not want to either pinch or scroll.
+  // To avoid small jiggles, it is also necessary to make sure that at least one
+  // of the fingers moved enough before a pinch or scroll update is created.
+  bool did_scroll = false;
+  for (int i = 0; i < kMaxGesturePoints; ++i) {
+    if (!points_[i].in_use() || !points_[i].DidScroll(event, 2))
+      continue;
+    did_scroll = true;
+    break;
+  }
+
+  if (!did_scroll)
+    return false;
+
   float distance = BoundingBoxDiagonal(bounding_box_);
 
   if (abs(distance - pinch_distance_current_) >=
       GestureConfiguration::min_pinch_update_distance_in_pixels()) {
     AppendPinchGestureUpdate(point,
         distance / pinch_distance_current_, gestures);
     pinch_distance_current_ = distance;
   } else {
     gfx::Point center = bounding_box_.CenterPoint();
     AppendScrollGestureUpdate(point, center, gestures);
@@ skipping 91 matching lines @@
     return;
 
   // Since long press timer has been started, there should be a non-NULL point.
   const GesturePoint* point = GetPointByPointId(0);
   if (!ui::gestures::IsInsideManhattanSquare(point->first_touch_position(),
       event.GetLocation()))
     long_press_timer_->Stop();
 }
 
 }  // namespace ui