ArgbEvaluator.java revision b31c3281d870e9abb673db239234d580dcc4feff 
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;
23import androidx.annotation.RestrictTo;
24
25/**
26 * This evaluator can be used to perform type interpolation between integer
27 * values that represent ARGB colors.
28 * @hide
29 */
30@RestrictTo(LIBRARY_GROUP)
31public class ArgbEvaluator implements TypeEvaluator {
32    private static final ArgbEvaluator sInstance = new ArgbEvaluator();
33
34    /**
35     * Returns an instance of <code>ArgbEvaluator</code> that may be used in
36     * {@link ValueAnimator#setEvaluator(TypeEvaluator)}. The same instance may
37     * be used in multiple <code>Animator</code>s because it holds no state.
38     *
39     * @return An instance of <code>ArgbEvalutor</code>.
40     */
41    public static ArgbEvaluator getInstance() {
42        return sInstance;
43    }
44
45    /**
46     * This function returns the calculated in-between value for a color
47     * given integers that represent the start and end values in the four
48     * bytes of the 32-bit int. Each channel is separately linearly interpolated
49     * and the resulting calculated values are recombined into the return value.
50     *
51     * @param fraction   The fraction from the starting to the ending values
52     * @param startValue A 32-bit int value representing colors in the
53     *                   separate bytes of the parameter
54     * @param endValue   A 32-bit int value representing colors in the
55     *                   separate bytes of the parameter
56     * @return A value that is calculated to be the linearly interpolated
57     * result, derived by separating the start and end values into separate
58     * color channels and interpolating each one separately, recombining the
59     * resulting values in the same way.
60     */
61    @Override
62    public Object evaluate(float fraction, Object startValue, Object endValue) {
63        int startInt = (Integer) startValue;
64        float startA = ((startInt >> 24) & 0xff) / 255.0f;
65        float startR = ((startInt >> 16) & 0xff) / 255.0f;
66        float startG = ((startInt >> 8) & 0xff) / 255.0f;
67        float startB = ((startInt) & 0xff) / 255.0f;
68
69        int endInt = (Integer) endValue;
70        float endA = ((endInt >> 24) & 0xff) / 255.0f;
71        float endR = ((endInt >> 16) & 0xff) / 255.0f;
72        float endG = ((endInt >> 8) & 0xff) / 255.0f;
73        float endB = ((endInt) & 0xff) / 255.0f;
74
75        // convert from sRGB to linear
76        startR = (float) Math.pow(startR, 2.2);
77        startG = (float) Math.pow(startG, 2.2);
78        startB = (float) Math.pow(startB, 2.2);
79
80        endR = (float) Math.pow(endR, 2.2);
81        endG = (float) Math.pow(endG, 2.2);
82        endB = (float) Math.pow(endB, 2.2);
83
84        // compute the interpolated color in linear space
85        float a = startA + fraction * (endA - startA);
86        float r = startR + fraction * (endR - startR);
87        float g = startG + fraction * (endG - startG);
88        float b = startB + fraction * (endB - startB);
89
90        // convert back to sRGB in the [0..255] range
91        a = a * 255.0f;
92        r = (float) Math.pow(r, 1.0 / 2.2) * 255.0f;
93        g = (float) Math.pow(g, 1.0 / 2.2) * 255.0f;
94        b = (float) Math.pow(b, 1.0 / 2.2) * 255.0f;
95
96        return Math.round(a) << 24 | Math.round(r) << 16 | Math.round(g) << 8 | Math.round(b);
97    }
98}
99