1/*
2 * Copyright (C) 2015 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.wearable.view;
18
19import android.animation.TimeInterpolator;
20import android.annotation.TargetApi;
21import android.os.Build;
22
23/**
24 * Interpolator that uses a Bezier derived S shaped curve.
25 * @hide
26 */
27@TargetApi(Build.VERSION_CODES.KITKAT_WATCH)
28class Gusterpolator implements TimeInterpolator {
29
30    /** An instance of {@link android.support.wearable.view.Gusterpolator}. */
31    public static final Gusterpolator INSTANCE = new Gusterpolator();
32
33    /**
34     * To avoid users of this class creating multiple copies needlessly, the constructor is
35     * private.
36     */
37    private Gusterpolator() {}
38
39    /**
40     * Lookup table values.
41     * Generated using a Bezier curve from (0,0) to (1,1) with control points:
42     * P0 (0,0)
43     * P1 (0.4, 0)
44     * P2 (0.2, 1.0)
45     * P3 (1.0, 1.0)
46     *
47     * Values sampled with x at regular intervals between 0 and 1.
48     */
49    private static final float[] VALUES = new float[] {
50        0.0f, 0.0002f, 0.0009f, 0.0019f, 0.0036f, 0.0059f, 0.0086f, 0.0119f, 0.0157f, 0.0209f,
51        0.0257f, 0.0321f, 0.0392f, 0.0469f, 0.0566f, 0.0656f, 0.0768f, 0.0887f, 0.1033f, 0.1186f,
52        0.1349f, 0.1519f, 0.1696f, 0.1928f, 0.2121f, 0.237f, 0.2627f, 0.2892f, 0.3109f, 0.3386f,
53        0.3667f, 0.3952f, 0.4241f, 0.4474f, 0.4766f, 0.5f, 0.5234f, 0.5468f, 0.5701f, 0.5933f,
54        0.6134f, 0.6333f, 0.6531f, 0.6698f, 0.6891f, 0.7054f, 0.7214f, 0.7346f, 0.7502f, 0.763f,
55        0.7756f, 0.7879f, 0.8f, 0.8107f, 0.8212f, 0.8326f, 0.8415f, 0.8503f, 0.8588f, 0.8672f,
56        0.8754f, 0.8833f, 0.8911f, 0.8977f, 0.9041f, 0.9113f, 0.9165f, 0.9232f, 0.9281f, 0.9328f,
57        0.9382f, 0.9434f, 0.9476f, 0.9518f, 0.9557f, 0.9596f, 0.9632f, 0.9662f, 0.9695f, 0.9722f,
58        0.9753f, 0.9777f, 0.9805f, 0.9826f, 0.9847f, 0.9866f, 0.9884f, 0.9901f, 0.9917f, 0.9931f,
59        0.9944f, 0.9955f, 0.9964f, 0.9973f, 0.9981f, 0.9986f, 0.9992f, 0.9995f, 0.9998f, 1.0f, 1.0f
60    };
61
62    private static final float STEP_SIZE = 1.0f / (VALUES.length - 1);
63
64    @Override
65    public float getInterpolation(float input) {
66        if (input >= 1.0f) {
67            return 1.0f;
68        }
69
70        if (input <= 0f) {
71            return 0f;
72        }
73
74        int position = Math.min(
75                (int)(input * (VALUES.length - 1)),
76                VALUES.length - 2);
77
78        float quantized = position * STEP_SIZE;
79        float difference = input - quantized;
80        float weight = difference / STEP_SIZE;
81
82        return VALUES[position] + weight * (VALUES[position + 1] - VALUES[position]);
83    }
84}
85