[Android] Perform eager gesture recognition on MotionEvents

content/browser/renderer_host/input/gesture_event_packet.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_packet.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) {

[tdresser, 2014/01/16 14:31:45]

nit: "IsTouchSequenceStart" probably makes more sense.

[jdduke (slow), 2014/01/16 17:17:53]

Done.

+  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 IsTriggeredByTimeout(const WebGestureEvent& event) {
+  switch (event.type) {
+    case WebInputEvent::GestureShowPress:
+    case WebInputEvent::GestureLongPress:
+    case WebInputEvent::GestureTapUnconfirmed:
+    case WebInputEvent::GestureTapCancel:
+      // A GestureTapCancel may be triggered by the loss of window focus
+      //   (e.g., following a GestureLongPress).
+      // TODO(jdduke): Eliminate this corner case, instead relying on the
+      // GestureEventQueue to cancel the tap sequence if necessary.
+      return true;
+    default:
+      break;
+  }
+  return false;
+}
+
+GestureEventPacket::GestureSource
+ToGestureSource(const WebTouchEvent& event) {
+  // TODO(jdduke): Use GestureTapDown as a new sequence marker?

[tdresser, 2014/01/16 14:31:45]

Agreed, that sounds simpler.

+  return IsTouchSequenceBegin(event) ? GestureEventPacket::TOUCH_BEGIN
+                                     : GestureEventPacket::TOUCH;
+}
+
+GestureEventPacket::GestureSource
+ToGestureSource(const WebGestureEvent& event) {
+  return IsTriggeredByTimeout(event) ? GestureEventPacket::TOUCH_TIMEOUT
+                                     : GestureEventPacket::SYNTHETIC;
+}
+
+}  // namespace
+
+GestureEventPacket::GestureEventPacket(GestureSource source)
+    : gesture_count_(0),
+      gesture_source_(source) {}
+
+GestureEventPacket::GestureEventPacket()
+    : gesture_count_(0),
+      gesture_source_(GESTURE_SOURCE_DEFAULT) {}
+
+GestureEventPacket::~GestureEventPacket() {}
+
+void GestureEventPacket::Push(const blink::WebGestureEvent& gesture) {
+  DCHECK_LT(gesture_count_, kMaxGesturesPerTouch);

[tdresser, 2014/01/16 14:31:45]

Is it reasonable to make this a CHECK_LT? I'm pretty likely to add a new gesture
that bumps us over 5 gestures per touch, test on device in release mode, and get
extremely confused.

[jdduke (slow), 2014/01/16 17:17:53]

Yeah.

+  gestures_[gesture_count_++] = gesture;
+}
+
+GestureEventPacket GestureEventPacket::FromTouch(const WebTouchEvent& event) {
+  return GestureEventPacket(ToGestureSource(event));
+}
+
+GestureEventPacket GestureEventPacket::FromGesture(
+    const WebGestureEvent& event) {
+  GestureEventPacket packet(ToGestureSource(event));
+  packet.Push(event);
+  return packet;
+}
+
+}  // namespace content