AnticipateInterpolator.java revision 8b0662878eae69ab62e859b07165f086ea65cad5 
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;
22
23/**
24 * An interpolator where the change starts backward then flings forward.
25 */
26public class AnticipateInterpolator implements Interpolator {
27    private final float mTension;
28
29    public AnticipateInterpolator() {
30        mTension = 2.0f;
31    }
32
33    /**
34     * @param tension Amount of anticipation. When tension equals 0.0f, there is
35     *                no anticipation and the interpolator becomes a simple
36     *                acceleration interpolator.
37     */
38    public AnticipateInterpolator(float tension) {
39        mTension = tension;
40    }
41
42    public AnticipateInterpolator(Context context, AttributeSet attrs) {
43        TypedArray a = context.obtainStyledAttributes(attrs,
44                com.android.internal.R.styleable.AnticipateInterpolator);
45
46        mTension =
47                a.getFloat(com.android.internal.R.styleable.AnticipateInterpolator_tension, 2.0f);
48
49        a.recycle();
50    }
51
52    public float getInterpolation(float t) {
53        // a(t) = t * t * ((tension + 1) * t - tension)
54        return t * t * ((mTension + 1) * t - mTension);
55    }
56}
57