core/java/android/view/animation/AnticipateInterpolator.java

/*
 * Copyright (C) 2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.view.animation;

import android.content.Context;
import android.content.res.TypedArray;
import android.util.AttributeSet;

/**
 * An interpolator where the change starts backward then flings forward.
 */
public class AnticipateInterpolator implements Interpolator {
    private final float mTension;

    public AnticipateInterpolator() {
        mTension = 2.0f;
    }

    /**
     * @param tension Amount of anticipation. When tension equals 0.0f, there is
     *                no anticipation and the interpolator becomes a simple
     *                acceleration interpolator.
     */
    public AnticipateInterpolator(float tension) {
        mTension = tension;
    }

    public AnticipateInterpolator(Context context, AttributeSet attrs) {
        TypedArray a = context.obtainStyledAttributes(attrs,
                com.android.internal.R.styleable.AnticipateInterpolator);

        mTension =
                a.getFloat(com.android.internal.R.styleable.AnticipateInterpolator_tension, 2.0f);

        a.recycle();
    }

    public float getInterpolation(float t) {
        // a(t) = t * t * ((tension + 1) * t - tension)
        return t * t * ((mTension + 1) * t - mTension);
    }
}