[ash-md] Adds support for gesture to move selection in overview mode

ash/wm/gestures/overview_gesture_handler.cc

 // Copyright 2013 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 "ash/wm/gestures/overview_gesture_handler.h"
 
 #include "ash/common/wm/overview/window_selector_controller.h"
 #include "ash/common/wm_shell.h"
 #include "ui/events/event.h"
 #include "ui/events/event_constants.h"
 
 namespace ash {
-namespace {
 
-// The threshold before engaging overview on a three finger swipe on the
-// touchpad.
-const float kSwipeThresholdPixels = 300;
+// The threshold before engaging overview with a touchpad three-finger scroll.
+float OverviewGestureHandler::vertical_threshold_pixels_ = 300;
 
-}  // namespace
+// The threshold before moving selector horizontally when using a touchpad
+// two or three-finger scroll.
+float OverviewGestureHandler::horizontal_threshold_pixels_ = 150;
 
 OverviewGestureHandler::OverviewGestureHandler() : scroll_x_(0), scroll_y_(0) {}
 
 OverviewGestureHandler::~OverviewGestureHandler() {}
 
 bool OverviewGestureHandler::ProcessScrollEvent(const ui::ScrollEvent& event) {
   if (event.type() == ui::ET_SCROLL_FLING_START ||
-      event.type() == ui::ET_SCROLL_FLING_CANCEL || event.finger_count() != 3) {
+      event.type() == ui::ET_SCROLL_FLING_CANCEL ||
+      (event.finger_count() != 2 && event.finger_count() != 3)) {

[tdanderson, 2017/02/08 23:14:19]

If you're going to start permitting two-finger scrolling to move the selection
widget, given that the grid is two-dimensional, I would expect two-finger
horizontal scrolls to be able to move the selection widget up/down. I think the
general model of two-finger scrolling is that it works in both dimensions (think
two-finger touchpad scrolling of a webpage); do you know of any counterexamples
to this in our UI?

The only other three-finger scrolling action I can think of is tab scrubbing in
Ash, and that only works in a single dimension, so I see no inconsistencies with
how you're making use of the three-finger scroll gesture in this CL.

[varkha, 2017/02/09 21:54:42]

Convinced - going back to requiring 3-finger gestures to scrub and enter / exit.

     scroll_x_ = scroll_y_ = 0;
     return false;
   }
 
   scroll_x_ += event.x_offset();
   scroll_y_ += event.y_offset();
 
-  // Horizontal swiping is ignored.
-  if (std::fabs(scroll_x_) >= std::fabs(scroll_y_)) {
-    scroll_x_ = scroll_y_ = 0;
-    return false;
-  }
-
   // Only allow swipe up to enter overview, down to exit. Ignore extra swiping

[tdanderson, 2017/02/08 23:14:19]

nit: update documentation and probably just merge this with the documentation on
line 41

[varkha, 2017/02/09 21:54:42]

Done.

   // in the wrong direction.
   WindowSelectorController* window_selector_controller =
       WmShell::Get()->window_selector_controller();
+
+  // Horizontal 2 or 3 finger scroll moves selection when in overview mode.
+  if (std::fabs(scroll_x_) >= std::fabs(scroll_y_)) {
+    if (!window_selector_controller->IsSelecting()) {
+      scroll_x_ = scroll_y_ = 0;
+      return false;
+    }
+
+    if (std::fabs(scroll_x_) < horizontal_threshold_pixels_)
+      return false;

[tdanderson, 2017/02/08 23:14:19]

nit: newline

[varkha, 2017/02/09 21:54:42]

Done.

+    window_selector_controller->IncrementSelection(
+        scroll_x_ / horizontal_threshold_pixels_);
+    scroll_x_ = scroll_y_ = 0;
+    return true;
+  }
+
+  // For the vertical scroll 3 fingers are required.
+  if (event.finger_count() != 3) {
+    scroll_x_ = scroll_y_ = 0;
+    return false;
+  }
+
   if (window_selector_controller->IsSelecting()) {
     if (scroll_y_ < 0)
       scroll_x_ = scroll_y_ = 0;
-    if (scroll_y_ < kSwipeThresholdPixels)
+    if (scroll_y_ < vertical_threshold_pixels_)
       return false;
   } else {
     if (scroll_y_ > 0)
       scroll_x_ = scroll_y_ = 0;
-    if (scroll_y_ > -kSwipeThresholdPixels)
+    if (scroll_y_ > -vertical_threshold_pixels_)
       return false;
   }
 
   // Reset scroll amount on toggling.
   scroll_x_ = scroll_y_ = 0;
   WmShell::Get()->RecordUserMetricsAction(UMA_TOUCHPAD_GESTURE_OVERVIEW);
+  if (window_selector_controller->IsSelecting() &&
+      window_selector_controller->AcceptSelection()) {
+    return true;
+  }
   window_selector_controller->ToggleOverview();
   return true;
 }
 
 }  // namespace ash