1/*
2 * Copyright (C) 2009 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.view.animation;
18
19import android.content.Context;
20import android.content.res.TypedArray;
21import android.util.AttributeSet;
22import static com.android.internal.R.styleable.AnticipateOvershootInterpolator_extraTension;
23import static com.android.internal.R.styleable.AnticipateOvershootInterpolator_tension;
24import static com.android.internal.R.styleable.AnticipateOvershootInterpolator;
25
26/**
27 * An interpolator where the change starts backward then flings forward and overshoots
28 * the target value and finally goes back to the final value.
29 */
30public class AnticipateOvershootInterpolator implements Interpolator {
31    private final float mTension;
32
33    public AnticipateOvershootInterpolator() {
34        mTension = 2.0f * 1.5f;
35    }
36
37    /**
38     * @param tension Amount of anticipation/overshoot. When tension equals 0.0f,
39     *                there is no anticipation/overshoot and the interpolator becomes
40     *                a simple acceleration/deceleration interpolator.
41     */
42    public AnticipateOvershootInterpolator(float tension) {
43        mTension = tension * 1.5f;
44    }
45
46    /**
47     * @param tension Amount of anticipation/overshoot. When tension equals 0.0f,
48     *                there is no anticipation/overshoot and the interpolator becomes
49     *                a simple acceleration/deceleration interpolator.
50     * @param extraTension Amount by which to multiply the tension. For instance,
51     *                     to get the same overshoot as an OvershootInterpolator with
52     *                     a tension of 2.0f, you would use an extraTension of 1.5f.
53     */
54    public AnticipateOvershootInterpolator(float tension, float extraTension) {
55        mTension = tension * extraTension;
56    }
57
58    public AnticipateOvershootInterpolator(Context context, AttributeSet attrs) {
59        TypedArray a = context.obtainStyledAttributes(attrs, AnticipateOvershootInterpolator);
60
61        mTension = a.getFloat(AnticipateOvershootInterpolator_tension, 2.0f) *
62                a.getFloat(AnticipateOvershootInterpolator_extraTension, 1.5f);
63
64        a.recycle();
65    }
66
67    private static float a(float t, float s) {
68        return t * t * ((s + 1) * t - s);
69    }
70
71    private static float o(float t, float s) {
72        return t * t * ((s + 1) * t + s);
73    }
74
75    public float getInterpolation(float t) {
76        // a(t, s) = t * t * ((s + 1) * t - s)
77        // o(t, s) = t * t * ((s + 1) * t + s)
78        // f(t) = 0.5 * a(t * 2, tension * extraTension), when t < 0.5
79        // f(t) = 0.5 * (o(t * 2 - 2, tension * extraTension) + 2), when t <= 1.0
80        if (t < 0.5f) return 0.5f * a(t * 2.0f, mTension);
81        else return 0.5f * (o(t * 2.0f - 2.0f, mTension) + 2.0f);
82    }
83}
84