DisplayList.java revision daf98e941e140e8739458126640183b9f296a2ab 
1/*
2 * Copyright (C) 2010 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
19/**
20 * A display lists records a series of graphics related operation and can replay
21 * them later. Display lists are usually built by recording operations on a
22 * {@link android.graphics.Canvas}. Replaying the operations from a display list
23 * avoids executing views drawing code on every frame, and is thus much more
24 * efficient.
25 *
26 * @hide
27 */
28public abstract class DisplayList {
29    /**
30     * Starts recording the display list. All operations performed on the
31     * returned canvas are recorded and stored in this display list.
32     *
33     * @return A canvas to record drawing operations.
34     */
35    abstract HardwareCanvas start();
36
37    /**
38     * Ends the recording for this display list. A display list cannot be
39     * replayed if recording is not finished.
40     */
41    abstract void end();
42
43    /**
44     * Indicates whether this display list can be replayed or not.
45     *
46     * @return True if the display list can be replayed, false otherwise.
47     *
48     * @see android.view.HardwareCanvas#drawDisplayList(DisplayList)
49     */
50    abstract boolean isReady();
51
52    /**
53     * Invalidates the display list, indicating that it should be repopulated
54     * with new drawing commands prior to being used again. Calling this method
55     * causes calls to {@link #isValid()} to return <code>false</code>.
56     */
57    abstract void invalidate();
58
59    /**
60     * Returns whether the display list is currently usable. If this returns false,
61     * the display list should be re-recorded prior to replaying it.
62     *
63     * @return boolean true if the display list is able to be replayed, false otherwise.
64     */
65    abstract boolean isValid();
66}
67