[Android] Perform eager gesture recognition on MotionEvents

content/browser/renderer_host/input/gesture_event_queue.h

+// 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.
+
+#ifndef CONTENT_BROWSER_RENDERER_HOST_INPUT_GESTURE_EVENT_QUEUE_H_
+#define CONTENT_BROWSER_RENDERER_HOST_INPUT_GESTURE_EVENT_QUEUE_H_
+
+#include <deque>
+
+#include "base/callback.h"
+#include "content/browser/renderer_host/input/gesture_event_packet.h"
+#include "content/common/content_export.h"
+#include "content/port/common/input_event_ack_state.h"
+#include "third_party/WebKit/public/web/WebInputEvent.h"
+
+namespace content {
+
+class CONTENT_EXPORT GestureEventQueueClient {
+ public:
+  virtual void ForwardGestureEvent(const blink::WebGestureEvent&) = 0;
+ protected:
+  virtual ~GestureEventQueueClient() {}
+};
+
+// Handles dispatch of gestures created by the system.  Gestures derived from
+// touches are forwarded or dropped depending on the disposition of the
+// generating touch sequence.  Synthetic gestures are dispatched immediately.
+class CONTENT_EXPORT GestureEventQueue {
+ public:
+  explicit GestureEventQueue(GestureEventQueueClient* client);
+  ~GestureEventQueue();
+
+  // To be called upon receipt of gesture-related events.  In particular,
+  // |packet| contains [0, n] gestures that correspond to a given event.  That
+  // event may be a touch, a touch timeout, or some other synthetic source.
+  // It is imperative that a single packet is received for *each* touch event,
+  // even those that did not produce a gesture.
+  void OnGestureEventPacket(const GestureEventPacket& packet);
+
+  // To be called upon receipt of *all* touch event acks.
+  void OnTouchEventAck(InputEventAckState ack_state);
+
+ private:
+  typedef base::Callback<void(const GestureEventPacket& packet)> PacketSender;

[tdresser, 2014/01/17 15:24:17]

I'm not super clear why you're adding a layer of abstraction here. Can you
comment this?

[jdduke (slow), 2014/01/17 19:38:04]

Well, I'd like the GestureSequence to perform dispatch of packets, as there may
be multiple per touch ack, e.g., for queued synthetic or timeout packets. There
are several ways to do this, my initial one had GEQ implement a simple
forwarding interface. I could also have the GestureSequence return a vector of
packets, but I'd prefer not to dynamically allocate anything. 

[tdresser, 2014/01/17 19:43:34]

Sounds reasonable.

+
+  // Utility class for tracking gesture events and dispositions for a single
+  // gesture sequence. A single sequence corresponds to all gestures created
+  // between the first finger down and the last finger up.
+  class GestureSequence {
+   public:
+    GestureSequence();
+    ~GestureSequence();
+
+    void Push(const GestureEventPacket& packet);
+    void OnTouchEventAck(InputEventAckState ack_state,
+                         const PacketSender& packet_handler);
+    bool IsGestureAllowed() const;
+    bool IsEmpty() const;
+
+   private:
+    std::deque<GestureEventPacket> sequence_;
+    InputEventAckState ack_state_;
+  };
+
+  void SendPacket(const GestureEventPacket& packet);
+  void SendGesture(const blink::WebGestureEvent& gesture);
+  void CancelTapIfNecessary();
+  void CancelFlingIfNecessary();
+  GestureSequence& Head();
+  GestureSequence& Tail();
+
+  GestureEventQueueClient* client_;
+  PacketSender packet_sender_;
+  std::deque<GestureSequence> sequences_;
+  bool outstanding_tap_;
+  bool outstanding_fling_;
+
+  DISALLOW_COPY_AND_ASSIGN(GestureEventQueue);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_RENDERER_HOST_INPUT_GESTURE_EVENT_QUEUE_H_