[Android] Perform eager gesture recognition on MotionEvents

content/browser/renderer_host/input/gesture_event_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/gesture_event_queue.h"
+
+#include "base/auto_reset.h"
+#include "base/bind.h"
+#include "base/logging.h"
+
+using blink::WebGestureEvent;
+using blink::WebInputEvent;
+using blink::WebTouchEvent;
+using blink::WebTouchPoint;
+
+namespace content {
+namespace {
+
+WebGestureEvent CreateGesture(WebInputEvent::Type type) {
+  DCHECK(WebInputEvent::isGestureEventType(type));
+  WebGestureEvent event;
+  event.type = type;
+  event.sourceDevice = WebGestureEvent::Touchscreen;
+  return event;
+}
+
+}  // namespace
+
+// GestureEventQueue
+
+GestureEventQueue::GestureEventQueue(GestureEventQueueClient* client)
+    : client_(client),
+      needs_tap_ending_event_(false),
+      needs_fling_ending_event_(false) {
+  DCHECK(client_);
+}
+
+GestureEventQueue::~GestureEventQueue() {}
+
+void GestureEventQueue::OnGestureEventPacket(const GestureEventPacket& packet) {
+  switch (packet.gesture_source()) {
+    case GestureEventPacket::TOUCH_BEGIN:
+      sequences_.push(GestureSequence());
+      break;
+
+    case GestureEventPacket::TOUCH:
+      break;
+
+    case GestureEventPacket::TOUCH_TIMEOUT:
+      // Handle the timeout packet immediately if the packet preceding the
+      // timeout has already been dispatched.
+      if (Tail().IsEmpty()) {
+        if (!Tail().IsGesturePrevented())
+          SendPacket(packet);
+        return;
+      }
+      break;
+
+    case GestureEventPacket::INVALID:
+      NOTREACHED() << "Invalid gesture packet detected.";
+      break;
+  }
+
+  Tail().Push(packet);
+}
+
+void GestureEventQueue::OnTouchEventAck(InputEventAckState ack_state) {
+  if (Head().IsEmpty()) {
+    CancelTapIfNecessary();
+    CancelFlingIfNecessary();
+    sequences_.pop();
+  }
+
+  GestureSequence& sequence = Head();
+  sequence.UpdateState(ack_state);
+
+  // Dispatch the packet corresponding to the ack'ed touch, as well as any
+  // additional timeout-based packets queued before the ack was received.
+  bool touch_packet_for_current_ack_handled = false;
+  while (!sequence.IsEmpty()) {
+    const GestureEventPacket& packet = sequence.Front();
+
+    if (packet.gesture_source() == GestureEventPacket::TOUCH_BEGIN ||
+        packet.gesture_source() == GestureEventPacket::TOUCH) {
+      // We should handle at most one touch-based packet corresponding to a
+      // given ack.
+      if (touch_packet_for_current_ack_handled)
+        break;
+      touch_packet_for_current_ack_handled = true;
+    }
+
+    if (!sequence.IsGesturePrevented())
+      SendPacket(packet);
+
+    sequence.Pop();
+  }
+  DCHECK(touch_packet_for_current_ack_handled);
+
+  // Immediately cancel a TapDown if TouchStart went unconsumed, but a
+  // subsequent TouchMove is consumed.
+  if (sequence.IsGesturePrevented())
+    CancelTapIfNecessary();
+}
+
+void GestureEventQueue::SendPacket(const GestureEventPacket& packet) {
+  for (size_t i = 0; i < packet.gesture_count(); ++i)
+    SendGesture(packet.gesture(i));
+}
+
+void GestureEventQueue::SendGesture(const WebGestureEvent& event) {
+  switch (event.type) {
+    case WebInputEvent::GestureLongTap:
+      CancelTapIfNecessary();
+      CancelFlingIfNecessary();
+      break;
+    case WebInputEvent::GestureTapDown:
+      needs_tap_ending_event_ = true;
+      break;
+    case WebInputEvent::GestureTapCancel:
+    case WebInputEvent::GestureTap:
+    case WebInputEvent::GestureTapUnconfirmed:
+    case WebInputEvent::GestureDoubleTap:
+      needs_tap_ending_event_ = false;
+      break;
+    case WebInputEvent::GestureScrollBegin:
+      CancelTapIfNecessary();
+      CancelFlingIfNecessary();
+      break;
+    case WebInputEvent::GestureFlingStart:
+      CancelFlingIfNecessary();
+      needs_fling_ending_event_ = true;
+      break;
+    case WebInputEvent::GestureFlingCancel:
+      needs_fling_ending_event_ = false;
+      break;
+    default:
+      break;
+  }
+  client_->ForwardGestureEvent(event);
+}
+
+void GestureEventQueue::CancelTapIfNecessary() {
+  if (!needs_tap_ending_event_)
+    return;
+
+  SendGesture(CreateGesture(WebInputEvent::GestureTapCancel));
+  DCHECK(!needs_tap_ending_event_);
+}
+
+void GestureEventQueue::CancelFlingIfNecessary() {
+  if (!needs_fling_ending_event_)
+    return;
+
+  SendGesture(CreateGesture(WebInputEvent::GestureFlingCancel));
+  DCHECK(!needs_fling_ending_event_);
+}
+
+GestureEventQueue::GestureSequence& GestureEventQueue::Head() {
+  DCHECK(!sequences_.empty());
+  return sequences_.front();
+}
+
+GestureEventQueue::GestureSequence& GestureEventQueue::Tail() {
+  DCHECK(!sequences_.empty());
+  return sequences_.back();
+}
+
+
+// GestureEventQueue::GestureSequence
+
+GestureEventQueue::GestureSequence::GestureSequence()
+    : state_(PENDING) {}
+
+GestureEventQueue::GestureSequence::~GestureSequence() {}
+
+void GestureEventQueue::GestureSequence::Push(
+    const GestureEventPacket& packet) {
+  packets_.push(packet);
+}
+
+void GestureEventQueue::GestureSequence::Pop() {
+  DCHECK(!IsEmpty());
+  packets_.pop();
+}
+
+const GestureEventPacket& GestureEventQueue::GestureSequence::Front() const {
+  DCHECK(!IsEmpty());
+  return packets_.front();
+}
+
+void GestureEventQueue::GestureSequence::UpdateState(
+    InputEventAckState ack_state) {
+  DCHECK_NE(INPUT_EVENT_ACK_STATE_UNKNOWN, ack_state);
+  // Permanent states will not be affected by subsequent ack's.
+  if (state_ != PENDING && state_ != ALLOWED_UNTIL_PREVENTED)
+    return;
+
+  // |NO_CONSUMER| should only be effective when the *first* touch is ack'ed.
+  if (state_ == PENDING &&
+      ack_state == INPUT_EVENT_ACK_STATE_NO_CONSUMER_EXISTS)
+    state_ = ALWAYS_ALLOWED;
+  else if (ack_state == INPUT_EVENT_ACK_STATE_CONSUMED)
+    state_ = ALWAYS_PREVENTED;
+  else
+    state_ = ALLOWED_UNTIL_PREVENTED;
+}
+
+bool GestureEventQueue::GestureSequence::IsGesturePrevented() const {
+  return state_ == ALWAYS_PREVENTED;
+}
+
+bool GestureEventQueue::GestureSequence::IsEmpty() const {
+  return packets_.empty();
+}
+
+}  // namespace content