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.animation;
18
19/**
20 * This evaluator can be used to perform type interpolation between integer
21 * values that represent ARGB colors.
22 */
23public class ArgbEvaluator implements TypeEvaluator {
24    private static final ArgbEvaluator sInstance = new ArgbEvaluator();
25
26    /**
27     * Returns an instance of <code>ArgbEvaluator</code> that may be used in
28     * {@link ValueAnimator#setEvaluator(TypeEvaluator)}. The same instance may
29     * be used in multiple <code>Animator</code>s because it holds no state.
30     * @return An instance of <code>ArgbEvalutor</code>.
31     *
32     * @hide
33     */
34    public static ArgbEvaluator getInstance() {
35        return sInstance;
36    }
37
38    /**
39     * This function returns the calculated in-between value for a color
40     * given integers that represent the start and end values in the four
41     * bytes of the 32-bit int. Each channel is separately linearly interpolated
42     * and the resulting calculated values are recombined into the return value.
43     *
44     * @param fraction The fraction from the starting to the ending values
45     * @param startValue A 32-bit int value representing colors in the
46     * separate bytes of the parameter
47     * @param endValue A 32-bit int value representing colors in the
48     * separate bytes of the parameter
49     * @return A value that is calculated to be the linearly interpolated
50     * result, derived by separating the start and end values into separate
51     * color channels and interpolating each one separately, recombining the
52     * resulting values in the same way.
53     */
54    public Object evaluate(float fraction, Object startValue, Object endValue) {
55        int startInt = (Integer) startValue;
56        int startA = (startInt >> 24) & 0xff;
57        int startR = (startInt >> 16) & 0xff;
58        int startG = (startInt >> 8) & 0xff;
59        int startB = startInt & 0xff;
60
61        int endInt = (Integer) endValue;
62        int endA = (endInt >> 24) & 0xff;
63        int endR = (endInt >> 16) & 0xff;
64        int endG = (endInt >> 8) & 0xff;
65        int endB = endInt & 0xff;
66
67        return (int)((startA + (int)(fraction * (endA - startA))) << 24) |
68                (int)((startR + (int)(fraction * (endR - startR))) << 16) |
69                (int)((startG + (int)(fraction * (endG - startG))) << 8) |
70                (int)((startB + (int)(fraction * (endB - startB))));
71    }
72}