Support double-tap to click in touch accessibility controller.

ui/chromeos/touch_exploration_controller.h

Index: ui/chromeos/touch_exploration_controller.h
diff --git a/ui/chromeos/touch_exploration_controller.h b/ui/chromeos/touch_exploration_controller.h
index d6fa8af0da7fd47ed933019d57ea2d1cece9efc0..083c79d5818f67fe1d332c2e81634c7b5a883c4d 100644
--- a/ui/chromeos/touch_exploration_controller.h
+++ b/ui/chromeos/touch_exploration_controller.h
@@ -5,9 +5,11 @@
 #ifndef UI_CHROMEOS_TOUCH_EXPLORATION_CONTROLLER_H_
 #define UI_CHROMEOS_TOUCH_EXPLORATION_CONTROLLER_H_
 
+#include "base/timer/timer.h"
 #include "base/values.h"
 #include "ui/chromeos/ui_chromeos_export.h"
 #include "ui/events/event_rewriter.h"
+#include "ui/events/gesture_detection/gesture_detector.h"
 #include "ui/gfx/geometry/point.h"
 
 namespace aura {
@@ -17,17 +19,52 @@ class Window;
 namespace ui {
 
 class Event;
+class TouchEvent;
 
 // TouchExplorationController is used in tandem with "Spoken Feedback" to
-// make the touch UI accessible. TouchExplorationController rewrites the
-// incoming touch events as follows:
-// - When one finger is touching the screen, touch events are converted to mouse
-//   moves. This is the "Touch Exploration Mode". (The idea is that mouse moves
-//   will be subsequently used by another component to move focus between UI
-//   elements, and the elements will be read out to the user.)
-// - When more than one finger is touching the screen, touches from the
-//   first (i.e. "oldest") finger are ignored, and the other touches go through
-//   as is.
+// make the touch UI accessible.
+//
+// At a high-level, single-finger events are used for accessibility -
+// exploring the screen gets turned into mouse moves (which can then be
+// spoken by an accessibility service running), a double-tap simulates a
+// click, and gestures can be used to send high-level accessibility commands.
+// Whenever two or more fingers are pressed, the events are passed through

[mfomitchev, 2014/05/28 17:47:45]

This doesn't seem entirely accurate - the minus one is applied iff the second
finger is pressed within the grace period.

[dmazzoni, 2014/06/04 22:46:27]

I tried to clarify, and I also tried to make it more clear that this is the
short version, which glosses over details like the grace period.

+// withone finger removed - so if you swipe down with two fingers, the

[mfomitchev, 2014/05/28 17:47:45]

"withone" - missing space

[dmazzoni, 2014/06/04 22:46:27]

Done.

+// running app will see a one-finger swipe.
+//
+// Here are the details of the implementation:
+//
+// When the first touch is pressed, a 300 ms grace period timer starts.
+//
+// If the user keeps their finger down for more than 300 ms and doesn't
+// perform a gesture in that time, they enter touch exploration mode, and

[mfomitchev, 2014/05/28 17:47:45]

I'd say smth like "supported accessibility gesture" instead of "gesture" 

[dmazzoni, 2014/06/04 22:46:27]

Done.

+// all movements are translated into synthesized mouse move events.
+//
+// Also, if the user moves their single finger outside a certain slop region

[mfomitchev, 2014/05/28 17:47:45]

This won't be accurate once we support swipe gestures, since a swipe gesture
isn't performed until the finger is lifted.

[dmazzoni, 2014/06/04 22:46:27]

True, but let's update the comment then.

+// (without performing a gesture), they enter touch exploration mode earlier
+// than 300 ms.
+//
+// If the user taps and releases their finger, after 300 ms from the initial
+// touch, a single mouse move is fired.
+//
+// If the user double-taps, the second tap is passed through, allowing the
+// user to click - however, the double-tap location is changed to the location
+// of the last successful touch exploration - that allows the user to explore
+// anywhere on the screen, hear its description, then double-tap anywhere
+// to activate it.
+//
+// If the user adds a second finger during the grace period, they enter
+// passthrough mode. In this mode, the first finger is ignored but all
+// additional touch events are mostly passed through unmodified. So a
+// two-finger scroll gets passed through as a one-finger scroll. However,
+// once in passthrough mode, if one finger is released, the remaining finger

[mfomitchev, 2014/05/28 17:47:45]

"remaining fingers continue"

[dmazzoni, 2014/06/04 22:46:27]

Done.

+// continues to pass through events, allowing the user to start a scroll
+// with two fingers but finish it with one. Sometimes this requires rewriting
+// the touch ids.
+//
+// Once either touch exploration or passthrough mode has been activated,
+// it remains in that mode until all fingers have been released.
+//
 // The caller is expected to retain ownership of instances of this class and
 // destroy them before |root_window| is destroyed.
 class UI_CHROMEOS_EXPORT TouchExplorationController :
@@ -48,16 +85,85 @@ class UI_CHROMEOS_EXPORT TouchExplorationController :
   virtual ui::EventRewriteStatus NextDispatchEvent(
       const ui::Event& last_event, scoped_ptr<ui::Event>* new_event) OVERRIDE;
 
+  // Event handlers based on the current state - see State, below.
+  ui::EventRewriteStatus OnNoFingersDown(
+      const ui::TouchEvent& event, scoped_ptr<ui::Event>* rewritten_event);
+  ui::EventRewriteStatus OnGracePeriod(
+      const ui::TouchEvent& event, scoped_ptr<ui::Event>* rewritten_event);
+  ui::EventRewriteStatus OnTouchExploration(
+      const ui::TouchEvent& event, scoped_ptr<ui::Event>* rewritten_event);
+  ui::EventRewriteStatus OnPassthroughMinusOne(
+      const ui::TouchEvent& event, scoped_ptr<ui::Event>* rewritten_event);
+  ui::EventRewriteStatus OnSingleTapPending(
+      const ui::TouchEvent& event, scoped_ptr<ui::Event>* rewritten_event);
+  ui::EventRewriteStatus OnDoubleTapPressed(
+      const ui::TouchEvent& event, scoped_ptr<ui::Event>* rewritten_event);
+
+  // This timer is started every time we get the first press event, and
+  // it fires after the double-click timeout elapses (300 ms by default).
+  // If the user taps and releases within 300 ms and doesn't press again,
+  // we treat that as a single mouse move (touch exploration) event.
+  void OnTapTimerFired();
+
+  enum State {
+    // No fingers are down and no events are pending.
+    NO_FINGERS_DOWN,
+
+    // A single finger is down, but we're not yet sure if this is going
+    // to be touch exploration or something else.
+    GRACE_PERIOD,

[mfomitchev, 2014/05/28 17:47:45]

IMHO the naming is a bit confusing, since GRACE_PERIOD and SINGLE_TAP_PENDING
are both in "grace period", and DOUBLE_TAP_PASSED could be in grace period as
well. Perhaps rename these to SINGLE_TAP_PRESSED, SINGLE_TAP_RELEASED,
DOUBLE_TAP_PRESSED?

[dmazzoni, 2014/06/04 22:46:27]

I like that, thanks.

+
+    // A single finger is down and after the grace period the user

[mfomitchev, 2014/05/28 17:47:45]

You could have multiple fingers down in this mode, you only need to have one
down during the grace period...

[dmazzoni, 2014/06/04 22:46:27]

Done.

+    // hasn't added a second finger or moved the finger too rapidly.
+    // We're now in touch exploration mode until this finger is lifted.

[mfomitchev, 2014/05/28 17:47:45]

"until all fingers are lifted"

[dmazzoni, 2014/06/04 22:46:27]

Done.

+    TOUCH_EXPLORATION,

[mfomitchev, 2014/05/28 17:47:45]

I'd move this down next to PASSTHROUGH_MINUS_ONE - IMHO the ordering/grouping
would be more logical that way.

[dmazzoni, 2014/06/04 22:46:27]

Done.

+
+    // The user pressed and released a single finger - a tap - but we have

[mfomitchev, 2014/05/28 17:47:45]

This sounds a bit confusing IMHO. I'd say like "..wait until the end of the
grace period to allow the user to tap the second time. If the second tap doesn't
occur within the grace period, we dispatch a mouse move at the location of the
first tap".

[dmazzoni, 2014/06/04 22:46:27]

Done.

+    // to wait until the end of the grace period before we will rewrite this
+    // as touch exploration, in case it's actually the first tap of a mouse
+    // move.
+    SINGLE_TAP_PENDING,
+
+    // The user tapped once, and before the grace period expired, pressed
+    // one finger down to begin a double-tap, but has not released it yet.
+    DOUBLE_TAP_PRESSED,
+
+    // The user placed two or more fingers down within the grace period.
+    // We're now in passthrough mode until all fingers are lifted. When
+    // two ore more fingers are down, we subtract one finger but otherwise

[mfomitchev, 2014/05/28 17:47:45]

Doesn't seem like this is entirely accurate - based on implementation it looks
like we only substract one finger until one finger is released.

[dmazzoni, 2014/06/04 22:46:27]

Fixed.

FWIW, we may need to tweak this -the mouse move caused by rewriting one finger
as another is something resulting in strange effects like an unwanted pinch. But
let's save that for the next change.

+    // pass through all events unchanged.
+    PASSTHROUGH_MINUS_ONE,
+  };
+
+  aura::Window* root_window_;
+
   // A set of touch ids for fingers currently touching the screen.
   std::vector<int> touch_ids_;
 
   // Map of touch ids to their last known location.
   std::map<int, gfx::PointF> touch_locations_;
 
-  // Initialized from RewriteEvent() and dispatched in NextDispatchEvent().
-  scoped_ptr<ui::Event> next_dispatch_event_;
+  // A map from the actual touch ids to the rewritten touch ids when in

[mfomitchev, 2014/05/28 17:47:45]

Hmm.. why change touch ids?

+  // "passthrough minus one" mode, where we pass through two-finger gestures
+  // as if they were one, and so on.
+  std::map<int, int> touch_id_map_;
 
-  aura::Window* root_window_;
+  // The current state.
+  State state_;
+
+  // A copy of the event from the initial touch press.
+  scoped_ptr<ui::TouchEvent> initial_press_;
+
+  // The last location where we synthesized a mouse move event.
+  // When the user double-taps, we send the passed-through tap here.
+  gfx::PointF last_touch_exploration_location_;
+
+  // A timer to fire the mouse move event after the double-tap delay.
+  base::OneShotTimer<TouchExplorationController> tap_timer_;
+
+  // A default gesture detector config, so we can share the same
+  // timeout and pixel slop constants.
+  ui::GestureDetector::Config gesture_detector_config_;
 
   DISALLOW_COPY_AND_ASSIGN(TouchExplorationController);
 };