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