ArgbEvaluator.java revision d0ff41c40660288c3bae27e5c3bc328a464eab03 
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        float startA = ((startInt >> 24) & 0xff) / 255.0f;
57        float startR = ((startInt >> 16) & 0xff) / 255.0f;
58        float startG = ((startInt >>  8) & 0xff) / 255.0f;
59        float startB = ( startInt        & 0xff) / 255.0f;
60
61        int endInt = (Integer) endValue;
62        float endA = ((endInt >> 24) & 0xff) / 255.0f;
63        float endR = ((endInt >> 16) & 0xff) / 255.0f;
64        float endG = ((endInt >>  8) & 0xff) / 255.0f;
65        float endB = ( endInt        & 0xff) / 255.0f;
66
67        // convert from sRGB to linear
68        startR = (float) Math.pow(startR, 2.2);
69        startG = (float) Math.pow(startG, 2.2);
70        startB = (float) Math.pow(startB, 2.2);
71
72        endR = (float) Math.pow(endR, 2.2);
73        endG = (float) Math.pow(endG, 2.2);
74        endB = (float) Math.pow(endB, 2.2);
75
76        // compute the interpolated color in linear space
77        float a = startA + fraction * (endA - startA);
78        float r = startR + fraction * (endR - startR);
79        float g = startG + fraction * (endG - startG);
80        float b = startB + fraction * (endB - startB);
81
82        // convert back to sRGB in the [0..255] range
83        a = a * 255.0f;
84        r = (float) Math.pow(r, 1.0 / 2.2) * 255.0f;
85        g = (float) Math.pow(g, 1.0 / 2.2) * 255.0f;
86        b = (float) Math.pow(b, 1.0 / 2.2) * 255.0f;
87
88        return Math.round(a) << 24 | Math.round(r) << 16 | Math.round(g) << 8 | Math.round(b);
89    }
90}