ArgbEvaluator.java revision 1f1b5540916924b36bc81cc3edb4f02245116dde 
1/*
2 * Copyright (C) 2017 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 androidx.vectordrawable.graphics.drawable;
18
19import static androidx.annotation.RestrictTo.Scope.LIBRARY_GROUP;
20
21import android.animation.TypeEvaluator;
22import android.animation.ValueAnimator;
23
24import androidx.annotation.RestrictTo;
25
26/**
27 * This evaluator can be used to perform type interpolation between integer
28 * values that represent ARGB colors.
29 * @hide
30 */
31@RestrictTo(LIBRARY_GROUP)
32public class ArgbEvaluator implements TypeEvaluator {
33    private static final ArgbEvaluator sInstance = new ArgbEvaluator();
34
35    /**
36     * Returns an instance of <code>ArgbEvaluator</code> that may be used in
37     * {@link ValueAnimator#setEvaluator(TypeEvaluator)}. The same instance may
38     * be used in multiple <code>Animator</code>s because it holds no state.
39     *
40     * @return An instance of <code>ArgbEvalutor</code>.
41     */
42    public static ArgbEvaluator getInstance() {
43        return sInstance;
44    }
45
46    /**
47     * This function returns the calculated in-between value for a color
48     * given integers that represent the start and end values in the four
49     * bytes of the 32-bit int. Each channel is separately linearly interpolated
50     * and the resulting calculated values are recombined into the return value.
51     *
52     * @param fraction   The fraction from the starting to the ending values
53     * @param startValue A 32-bit int value representing colors in the
54     *                   separate bytes of the parameter
55     * @param endValue   A 32-bit int value representing colors in the
56     *                   separate bytes of the parameter
57     * @return A value that is calculated to be the linearly interpolated
58     * result, derived by separating the start and end values into separate
59     * color channels and interpolating each one separately, recombining the
60     * resulting values in the same way.
61     */
62    @Override
63    public Object evaluate(float fraction, Object startValue, Object endValue) {
64        int startInt = (Integer) startValue;
65        float startA = ((startInt >> 24) & 0xff) / 255.0f;
66        float startR = ((startInt >> 16) & 0xff) / 255.0f;
67        float startG = ((startInt >> 8) & 0xff) / 255.0f;
68        float startB = ((startInt) & 0xff) / 255.0f;
69
70        int endInt = (Integer) endValue;
71        float endA = ((endInt >> 24) & 0xff) / 255.0f;
72        float endR = ((endInt >> 16) & 0xff) / 255.0f;
73        float endG = ((endInt >> 8) & 0xff) / 255.0f;
74        float endB = ((endInt) & 0xff) / 255.0f;
75
76        // convert from sRGB to linear
77        startR = (float) Math.pow(startR, 2.2);
78        startG = (float) Math.pow(startG, 2.2);
79        startB = (float) Math.pow(startB, 2.2);
80
81        endR = (float) Math.pow(endR, 2.2);
82        endG = (float) Math.pow(endG, 2.2);
83        endB = (float) Math.pow(endB, 2.2);
84
85        // compute the interpolated color in linear space
86        float a = startA + fraction * (endA - startA);
87        float r = startR + fraction * (endR - startR);
88        float g = startG + fraction * (endG - startG);
89        float b = startB + fraction * (endB - startB);
90
91        // convert back to sRGB in the [0..255] range
92        a = a * 255.0f;
93        r = (float) Math.pow(r, 1.0 / 2.2) * 255.0f;
94        g = (float) Math.pow(g, 1.0 / 2.2) * 255.0f;
95        b = (float) Math.pow(b, 1.0 / 2.2) * 255.0f;
96
97        return Math.round(a) << 24 | Math.round(r) << 16 | Math.round(g) << 8 | Math.round(b);
98    }
99}
100