1/*
2 * Copyright (C) 2013 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.support.v4.widget;
18
19import android.view.animation.Interpolator;
20
21/**
22 * A pre-baked bezier-curved interpolator for indeterminate progress animations.
23 */
24final class BakedBezierInterpolator implements Interpolator {
25    private static final BakedBezierInterpolator INSTANCE = new BakedBezierInterpolator();
26
27    public final static BakedBezierInterpolator getInstance() {
28        return INSTANCE;
29    }
30
31    /**
32     * Use getInstance instead of instantiating.
33     */
34    private BakedBezierInterpolator() {
35        super();
36    }
37
38    /**
39     * Lookup table values.
40     * Generated using a Bezier curve from (0,0) to (1,1) with control points:
41     * P0 (0,0)
42     * P1 (0.4, 0)
43     * P2 (0.2, 1.0)
44     * P3 (1.0, 1.0)
45     *
46     * Values sampled with x at regular intervals between 0 and 1.
47     */
48    private static final float[] VALUES = new float[] {
49        0.0f, 0.0002f, 0.0009f, 0.0019f, 0.0036f, 0.0059f, 0.0086f, 0.0119f, 0.0157f, 0.0209f,
50        0.0257f, 0.0321f, 0.0392f, 0.0469f, 0.0566f, 0.0656f, 0.0768f, 0.0887f, 0.1033f, 0.1186f,
51        0.1349f, 0.1519f, 0.1696f, 0.1928f, 0.2121f, 0.237f, 0.2627f, 0.2892f, 0.3109f, 0.3386f,
52        0.3667f, 0.3952f, 0.4241f, 0.4474f, 0.4766f, 0.5f, 0.5234f, 0.5468f, 0.5701f, 0.5933f,
53        0.6134f, 0.6333f, 0.6531f, 0.6698f, 0.6891f, 0.7054f, 0.7214f, 0.7346f, 0.7502f, 0.763f,
54        0.7756f, 0.7879f, 0.8f, 0.8107f, 0.8212f, 0.8326f, 0.8415f, 0.8503f, 0.8588f, 0.8672f,
55        0.8754f, 0.8833f, 0.8911f, 0.8977f, 0.9041f, 0.9113f, 0.9165f, 0.9232f, 0.9281f, 0.9328f,
56        0.9382f, 0.9434f, 0.9476f, 0.9518f, 0.9557f, 0.9596f, 0.9632f, 0.9662f, 0.9695f, 0.9722f,
57        0.9753f, 0.9777f, 0.9805f, 0.9826f, 0.9847f, 0.9866f, 0.9884f, 0.9901f, 0.9917f, 0.9931f,
58        0.9944f, 0.9955f, 0.9964f, 0.9973f, 0.9981f, 0.9986f, 0.9992f, 0.9995f, 0.9998f, 1.0f, 1.0f
59    };
60
61    private static final float STEP_SIZE = 1.0f / (VALUES.length - 1);
62
63    @Override
64    public float getInterpolation(float input) {
65        if (input >= 1.0f) {
66            return 1.0f;
67        }
68
69        if (input <= 0f) {
70            return 0f;
71        }
72
73        int position = Math.min(
74                (int)(input * (VALUES.length - 1)),
75                VALUES.length - 2);
76
77        float quantized = position * STEP_SIZE;
78        float difference = input - quantized;
79        float weight = difference / STEP_SIZE;
80
81        return VALUES[position] + weight * (VALUES[position + 1] - VALUES[position]);
82    }
83
84}
85