[Android] Perform eager gesture recognition on MotionEvents

content/browser/renderer_host/input/touch_to_gesture_queue.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 "content/browser/renderer_host/input/touch_to_gesture_queue.h"
+
+#include "base/auto_reset.h"
+#include "base/logging.h"
+#include "content/common/input/web_input_event_traits.h"
+
+using blink::WebGestureEvent;
+using blink::WebInputEvent;
+using blink::WebTouchEvent;
+using blink::WebTouchPoint;
+
+namespace content {
+namespace {
+
+bool IsTouchSequenceBegin(const WebTouchEvent& event) {
+  if (event.type != WebInputEvent::TouchStart)
+    return false;
+  if (!event.touchesLength)
+    return false;
+  for (size_t i = 0; i < event.touchesLength; i++) {
+    if (event.touches[i].state != WebTouchPoint::StatePressed)
+      return false;
+  }
+  return true;
+}
+
+bool IsScrollStart(const WebGestureEvent& event) {
+  return event.type == WebInputEvent::GestureScrollBegin;
+}
+
+bool IsFlingCancel(const WebGestureEvent& event) {
+  return event.type == WebInputEvent::GestureFlingCancel;
+}
+
+bool IsFlingStart(const WebGestureEvent& event) {
+  return event.type == WebInputEvent::GestureFlingStart;
+}
+
+bool IsTapStart(const WebGestureEvent& event) {
+  return event.type == WebInputEvent::GestureTapDown;
+}
+
+bool IsTapEnd(const WebGestureEvent& event) {
+  switch (event.type) {
+    case WebInputEvent::GestureTapCancel:
+    case WebInputEvent::GestureTap:
+    case WebInputEvent::GestureTapUnconfirmed:
+    case WebInputEvent::GestureDoubleTap:
+      return true;
+    default:
+      break;
+  }
+  return false;
+}
+
+bool IsTimeout(const WebGestureEvent& event) {

[tdresser, 2014/01/14 16:25:30]

Perhaps IsTimeout -> IsTriggeredByTimeout?

[jdduke (slow), 2014/01/14 23:24:03]

Done.

+  switch (event.type) {
+    case WebInputEvent::GestureShowPress:
+    case WebInputEvent::GestureLongPress:
+    case WebInputEvent::GestureTapUnconfirmed:
+      return true;
+    default:
+      break;
+  }
+  return false;
+}
+
+InputEventAckState Intersection(InputEventAckState ack_old,

[tdresser, 2014/01/14 16:25:30]

The word "Intersection" applied to an enum could be interpreted a couple
different ways. Perhaps |LeastConsumed| would be clearer? Any other ideas?

[jdduke (slow), 2014/01/14 23:24:03]

Hmm, I'll noodle on this.

+                                InputEventAckState ack_new) {
+  if (ack_new == INPUT_EVENT_ACK_STATE_UNKNOWN) {
+    NOTREACHED() << "New acks should never be undefined.";
+    return ack_old;
+  }
+
+  if (ack_old == INPUT_EVENT_ACK_STATE_UNKNOWN ||
+      ack_old == INPUT_EVENT_ACK_STATE_NOT_CONSUMED)
+    return ack_new;
+
+  // If a partial touch sequence has been consumed, or has no consumer,
+  // subsequent touches have no bearing on the overall gesture disposition.
+  return ack_old;
+}
+
+WebGestureEvent CreateGesture(WebInputEvent::Type type) {
+  DCHECK(WebInputEvent::isGestureEventType(type));
+  WebGestureEvent event;
+  event.type = type;
+  event.sourceDevice = WebGestureEvent::Touchscreen;
+  return event;
+}
+
+}  // namespace
+
+TouchToGestureQueue::TouchToGestureQueue(TouchToGestureQueueClient* client)
+    : client_(client),
+      handling_touch_event_(false),
+      outstanding_tap_(false),
+      outstanding_fling_(false) {
+  DCHECK(client_);
+}
+
+TouchToGestureQueue::~TouchToGestureQueue() {}
+
+void TouchToGestureQueue::OnTouchEventHandlingBegin(
+    const WebTouchEvent& event) {
+  DCHECK(!handling_touch_event_);
+  handling_touch_event_ = true;
+
+  if (IsTouchSequenceBegin(event))
+    sequences_.push_back(TouchToGestureSequence());
+
+  Tail().Push(event);
+}
+
+void TouchToGestureQueue::OnTouchEventHandlingEnd() {
+  DCHECK(handling_touch_event_);
+  DCHECK(!sequences_.empty());
+
+  handling_touch_event_ = false;
+  client_->ForwardTouchEvent(Tail().LastTouch());
+}
+
+void TouchToGestureQueue::OnGestureEvent(const WebGestureEvent& event) {
+  if (handling_touch_event_) {
+    Tail().Push(event);
+    return;
+  }
+
+  if (IsTimeout(event)) {
+    // Touches preceding the timeout event are still awaiting an ack.
+    if (!Tail().IsEmpty())
+      Tail().Push(event);
+    // Touches preceding the timeout have been handled and gestures are allowed.
+    else if (Tail().IsGestureAllowed())
+      ForwardGestureEvent(event);
+    // The timeout gesture should be dropped.
+    return;
+  }
+
+  // Synthetic gestures may be generated by the platform, in which case they
+  // should simply be forwarded immediately.
+  ForwardGestureEvent(event);
+}
+
+void TouchToGestureQueue::OnTouchEventAck(InputEventAckState ack_state) {
+  // Transition to the next touch sequence.  This transition is deferred
+  // until the ack in the event that the sequence receives a timeout event.
+  if (Head().IsEmpty()) {
+    CancelTapIfNecessary();
+    CancelFlingIfNecessary();
+    sequences_.pop_front();
+  }
+
+  // TODO(jdduke): Settle on touch-slop disposition behavior, crbug/333947.
+  TouchToGesture touch_to_gesture = Head().OnTouchEventAck(ack_state);
+  for (size_t i = 0; i < touch_to_gesture.gestures.size(); ++i)
+    ForwardGestureEvent(touch_to_gesture.gestures[i]);
+
+  // Immediately cancel a TapDown if TouchStart went unconsumed, but a
+  // subsequent TouchMove is consumed.
+  if (!Head().IsGestureAllowed())
+    CancelTapIfNecessary();
+}
+
+void TouchToGestureQueue::ForwardGestureEvent(const WebGestureEvent& event) {

[tdresser, 2014/01/14 16:25:30]

I don't think this is any more readable than a bigger switch statement which
explicitly tests all the event types. Having all those three line functions
feels a little unnecessary. I'm fine with this approach too though.

[jdduke (slow), 2014/01/14 23:24:03]

You're totally right, this originally started with just the tap queries, but a
switch is better.

+  if (IsTapStart(event))
+    outstanding_tap_ = true;
+  else if (IsTapEnd(event))
+    outstanding_tap_ = false;
+  else if (IsFlingStart(event))
+    outstanding_fling_ = true;
+  else if (IsFlingCancel(event))
+    outstanding_fling_ = false;
+  else if (IsScrollStart(event))
+    CancelTapIfNecessary();
+
+  client_->ForwardGestureEvent(event);
+}
+
+void TouchToGestureQueue::CancelTapIfNecessary() {
+  if (!outstanding_tap_)
+    return;
+
+  ForwardGestureEvent(CreateGesture(WebInputEvent::GestureTapCancel));
+  DCHECK(!outstanding_tap_);
+}
+
+void TouchToGestureQueue::CancelFlingIfNecessary() {
+  if (!outstanding_fling_)
+    return;
+
+  ForwardGestureEvent(CreateGesture(WebInputEvent::GestureFlingCancel));
+  DCHECK(!outstanding_fling_);
+}
+
+TouchToGestureQueue::TouchToGestureSequence& TouchToGestureQueue::Head() {
+  DCHECK(!sequences_.empty());
+  return sequences_.front();
+}
+
+TouchToGestureQueue::TouchToGestureSequence& TouchToGestureQueue::Tail() {
+  DCHECK(!sequences_.empty());
+  return sequences_.back();
+}
+
+TouchToGestureQueue::TouchToGestureSequence::TouchToGestureSequence()
+    : ack_state(INPUT_EVENT_ACK_STATE_UNKNOWN) {}
+
+TouchToGestureQueue::TouchToGestureSequence::~TouchToGestureSequence() {}
+
+void TouchToGestureQueue::TouchToGestureSequence::Push(
+    const blink::WebTouchEvent& event) {
+  TouchToGesture touch_to_gesture;
+  touch_to_gesture.touch = event;
+  sequence.push_back(touch_to_gesture);
+}
+
+void TouchToGestureQueue::TouchToGestureSequence::Push(
+    const blink::WebGestureEvent& event) {
+  DCHECK(!IsEmpty());
+  sequence.back().gestures.push_back(event);
+}
+
+TouchToGestureQueue::TouchToGesture
+TouchToGestureQueue::TouchToGestureSequence::OnTouchEventAck(
+    InputEventAckState new_ack_state) {
+  DCHECK(!IsEmpty());
+
+  ack_state = Intersection(ack_state, new_ack_state);
+  DCHECK_NE(ack_state, INPUT_EVENT_ACK_STATE_UNKNOWN);
+
+  TouchToGesture touch_to_gesture =
+      IsGestureAllowed() ? sequence.front() : TouchToGesture();
+  sequence.pop_front();
+  return touch_to_gesture;
+}
+
+bool TouchToGestureQueue::TouchToGestureSequence::IsGestureAllowed() const {
+  return ack_state == INPUT_EVENT_ACK_STATE_NO_CONSUMER_EXISTS ||
+         ack_state == INPUT_EVENT_ACK_STATE_NOT_CONSUMED;
+}
+
+bool TouchToGestureQueue::TouchToGestureSequence::IsEmpty() const {
+  return sequence.empty();
+}
+
+const blink::WebTouchEvent&
+TouchToGestureQueue::TouchToGestureSequence::LastTouch() const {
+  DCHECK(!IsEmpty());
+  return sequence.back().touch;
+}
+
+}  // namespace content