1/*
2 * Copyright (C) 2011 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package android.view;
18
19import dalvik.system.CloseGuard;
20
21import android.os.Looper;
22import android.os.MessageQueue;
23import android.util.Log;
24
25/**
26 * Provides a low-level mechanism for an application to receive display events
27 * such as vertical sync.
28 *
29 * The display event receive is NOT thread safe.  Moreover, its methods must only
30 * be called on the Looper thread to which it is attached.
31 *
32 * @hide
33 */
34public abstract class DisplayEventReceiver {
35    private static final String TAG = "DisplayEventReceiver";
36
37    private final CloseGuard mCloseGuard = CloseGuard.get();
38
39    private int mReceiverPtr;
40
41    // We keep a reference message queue object here so that it is not
42    // GC'd while the native peer of the receiver is using them.
43    private MessageQueue mMessageQueue;
44
45    private static native int nativeInit(DisplayEventReceiver receiver,
46            MessageQueue messageQueue);
47    private static native void nativeDispose(int receiverPtr);
48    private static native void nativeScheduleVsync(int receiverPtr);
49
50    /**
51     * Creates a display event receiver.
52     *
53     * @param looper The looper to use when invoking callbacks.
54     */
55    public DisplayEventReceiver(Looper looper) {
56        if (looper == null) {
57            throw new IllegalArgumentException("looper must not be null");
58        }
59
60        mMessageQueue = looper.getQueue();
61        mReceiverPtr = nativeInit(this, mMessageQueue);
62
63        mCloseGuard.open("dispose");
64    }
65
66    @Override
67    protected void finalize() throws Throwable {
68        try {
69            dispose();
70        } finally {
71            super.finalize();
72        }
73    }
74
75    /**
76     * Disposes the receiver.
77     */
78    public void dispose() {
79        if (mCloseGuard != null) {
80            mCloseGuard.close();
81        }
82        if (mReceiverPtr != 0) {
83            nativeDispose(mReceiverPtr);
84            mReceiverPtr = 0;
85        }
86        mMessageQueue = null;
87    }
88
89    /**
90     * Called when a vertical sync pulse is received.
91     * The recipient should render a frame and then call {@link #scheduleVsync}
92     * to schedule the next vertical sync pulse.
93     *
94     * @param timestampNanos The timestamp of the pulse, in the {@link System#nanoTime()}
95     * timebase.
96     * @param frame The frame number.  Increases by one for each vertical sync interval.
97     */
98    public void onVsync(long timestampNanos, int frame) {
99    }
100
101    /**
102     * Schedules a single vertical sync pulse to be delivered when the next
103     * display frame begins.
104     */
105    public void scheduleVsync() {
106        if (mReceiverPtr == 0) {
107            Log.w(TAG, "Attempted to schedule a vertical sync pulse but the display event "
108                    + "receiver has already been disposed.");
109        } else {
110            nativeScheduleVsync(mReceiverPtr);
111        }
112    }
113
114    // Called from native code.
115    @SuppressWarnings("unused")
116    private void dispatchVsync(long timestampNanos, int frame) {
117        onVsync(timestampNanos, frame);
118    }
119}
120