Eager Gesture Recognition on Aura

ui/events/gestures/gesture_provider_aura.cc

 // Copyright 2014 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/events/gestures/gesture_provider_aura.h"
 
 #include "base/auto_reset.h"
 #include "base/logging.h"
 #include "ui/events/event.h"
 #include "ui/events/gesture_detection/gesture_config_helper.h"
@@ skipping 10 matching lines @@
 }
 
 GestureProviderAura::~GestureProviderAura() {}
 
 bool GestureProviderAura::OnTouchEvent(const TouchEvent& event) {
   bool pointer_id_is_active = false;
   for (size_t i = 0; i < pointer_state_.GetPointerCount(); ++i) {
     if (event.touch_id() != pointer_state_.GetPointerId(i))
       continue;
     pointer_id_is_active = true;
+
+    // If this is a touchmove event, and it isn't different from the last
+    // event, ignore it.
+    if (event.type() == ET_TOUCH_MOVED &&
+        event.x() == pointer_state_.GetX(i) &&
+        event.y() == pointer_state_.GetY(i) &&
+        std::max(event.radius_x(), event.radius_y()) * 2 ==
+            pointer_state_.GetTouchMajor(i) &&
+        event.force() == pointer_state_.GetPressure(i)) {

[jdduke (slow), 2014/07/30 15:29:32]

How noisy are force/radius values compared to position? I'd rather we preserve
the logic we had in ui_events_helper.cc for now (only comparing the position),
and fold in the radius/pressure if we find that necessary in the future.

[tdresser, 2014/07/31 15:33:31]

The amount of noise depends entirely on the firmware configuration, but you're
right that there is frequently more noise in the radius and pressure.

It feels wrong to me to be artificially filtering out legitimate changes in
radius and pressure though. If we feel the signal is too noisy, maybe we should
be smoothing it?

That being said, I don't care particularly strongly about it, if you'd prefer
only looking at location, that's fine.

[jdduke (slow), 2014/07/31 16:19:02]

It's not that I feel strongly about it, more so that this patch introduces a
substantial behavior change, so the fewer additional differences we layer in,
the better.  We can always fix it in a follow-up patch, and you're probably
right that using the size here makes sense.

[tdresser, 2014/08/01 13:35:32]

Done.

+      return false;
+    }
     break;
   }
 
   if (event.type() == ET_TOUCH_PRESSED && pointer_id_is_active) {
     // Ignore touch press events if we already believe the pointer is down.
     return false;
   } else if (event.type() != ET_TOUCH_PRESSED && !pointer_id_is_active) {
     // We could have an active touch stream transfered to us, resulting in touch
     // move or touch up events without associated touch down events. Ignore
     // them.
@@ skipping 86 matching lines @@
 
   double double_tap_slop_square =
       GestureConfiguration::max_distance_between_taps_for_double_tap();
   double_tap_slop_square *= double_tap_slop_square;
   const float delta_x = previous_tap.x - current_tap.x;
   const float delta_y = previous_tap.y - current_tap.y;
   return (delta_x * delta_x + delta_y * delta_y < double_tap_slop_square);
 }
 
 }  // namespace content