AnticipateOvershootInterpolator.java revision e5e92602a41a4ddc7b42cd1c171a0edfbd09b8da 
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.Resources;
21import android.content.res.Resources.Theme;
22import android.content.res.TypedArray;
23import android.util.AttributeSet;
24
25import com.android.internal.view.animation.HasNativeInterpolator;
26import com.android.internal.view.animation.NativeInterpolatorFactory;
27import com.android.internal.view.animation.NativeInterpolatorFactoryHelper;
28
29import static com.android.internal.R.styleable.AnticipateOvershootInterpolator_extraTension;
30import static com.android.internal.R.styleable.AnticipateOvershootInterpolator_tension;
31import static com.android.internal.R.styleable.AnticipateOvershootInterpolator;
32
33/**
34 * An interpolator where the change starts backward then flings forward and overshoots
35 * the target value and finally goes back to the final value.
36 */
37@HasNativeInterpolator
38public class AnticipateOvershootInterpolator implements Interpolator, NativeInterpolatorFactory {
39    private final float mTension;
40
41    public AnticipateOvershootInterpolator() {
42        mTension = 2.0f * 1.5f;
43    }
44
45    /**
46     * @param tension Amount of anticipation/overshoot. When tension equals 0.0f,
47     *                there is no anticipation/overshoot and the interpolator becomes
48     *                a simple acceleration/deceleration interpolator.
49     */
50    public AnticipateOvershootInterpolator(float tension) {
51        mTension = tension * 1.5f;
52    }
53
54    /**
55     * @param tension Amount of anticipation/overshoot. When tension equals 0.0f,
56     *                there is no anticipation/overshoot and the interpolator becomes
57     *                a simple acceleration/deceleration interpolator.
58     * @param extraTension Amount by which to multiply the tension. For instance,
59     *                     to get the same overshoot as an OvershootInterpolator with
60     *                     a tension of 2.0f, you would use an extraTension of 1.5f.
61     */
62    public AnticipateOvershootInterpolator(float tension, float extraTension) {
63        mTension = tension * extraTension;
64    }
65
66    public AnticipateOvershootInterpolator(Context context, AttributeSet attrs) {
67        this(context.getResources(), context.getTheme(), attrs);
68    }
69
70    /** @hide */
71    public AnticipateOvershootInterpolator(Resources res, Theme theme, AttributeSet attrs) {
72        TypedArray a;
73        if (theme != null) {
74            a = theme.obtainStyledAttributes(attrs, AnticipateOvershootInterpolator, 0, 0);
75        } else {
76            a = res.obtainAttributes(attrs, AnticipateOvershootInterpolator);
77        }
78
79        mTension = a.getFloat(AnticipateOvershootInterpolator_tension, 2.0f) *
80                a.getFloat(AnticipateOvershootInterpolator_extraTension, 1.5f);
81
82        a.recycle();
83    }
84
85    private static float a(float t, float s) {
86        return t * t * ((s + 1) * t - s);
87    }
88
89    private static float o(float t, float s) {
90        return t * t * ((s + 1) * t + s);
91    }
92
93    public float getInterpolation(float t) {
94        // a(t, s) = t * t * ((s + 1) * t - s)
95        // o(t, s) = t * t * ((s + 1) * t + s)
96        // f(t) = 0.5 * a(t * 2, tension * extraTension), when t < 0.5
97        // f(t) = 0.5 * (o(t * 2 - 2, tension * extraTension) + 2), when t <= 1.0
98        if (t < 0.5f) return 0.5f * a(t * 2.0f, mTension);
99        else return 0.5f * (o(t * 2.0f - 2.0f, mTension) + 2.0f);
100    }
101
102    /** @hide */
103    @Override
104    public long createNativeInterpolator() {
105        return NativeInterpolatorFactoryHelper.createAnticipateOvershootInterpolator(mTension);
106    }
107}
108