core/java/android/animation/PointFEvaluator.java

/*
 * Copyright (C) 2013 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.animation;

import android.graphics.PointF;

/**
 * This evaluator can be used to perform type interpolation between <code>PointF</code> values.
 */
public class PointFEvaluator implements TypeEvaluator<PointF> {

    /**
     * When null, a new PointF is returned on every evaluate call. When non-null,
     * mPoint will be modified and returned on every evaluate.
     */
    private PointF mPoint;

    /**
     * Construct a PointFEvaluator that returns a new PointF on every evaluate call.
     * To avoid creating an object for each evaluate call,
     * {@link PointFEvaluator#PointFEvaluator(android.graphics.PointF)} should be used
     * whenever possible.
     */
    public PointFEvaluator() {
    }

    /**
     * Constructs a PointFEvaluator that modifies and returns <code>reuse</code>
     * in {@link #evaluate(float, android.graphics.PointF, android.graphics.PointF)} calls.
     * The value returned from
     * {@link #evaluate(float, android.graphics.PointF, android.graphics.PointF)} should
     * not be cached because it will change over time as the object is reused on each
     * call.
     *
     * @param reuse A PointF to be modified and returned by evaluate.
     */
    public PointFEvaluator(PointF reuse) {
        mPoint = reuse;
    }

    /**
     * This function returns the result of linearly interpolating the start and
     * end PointF values, with <code>fraction</code> representing the proportion
     * between the start and end values. The calculation is a simple parametric
     * calculation on each of the separate components in the PointF objects
     * (x, y).
     *
     * <p>If {@link #PointFEvaluator(android.graphics.PointF)} was used to construct
     * this PointFEvaluator, the object returned will be the <code>reuse</code>
     * passed into the constructor.</p>
     *
     * @param fraction   The fraction from the starting to the ending values
     * @param startValue The start PointF
     * @param endValue   The end PointF
     * @return A linear interpolation between the start and end values, given the
     *         <code>fraction</code> parameter.
     */
    @Override
    public PointF evaluate(float fraction, PointF startValue, PointF endValue) {
        float x = startValue.x + (fraction * (endValue.x - startValue.x));
        float y = startValue.y + (fraction * (endValue.y - startValue.y));

        if (mPoint != null) {
            mPoint.set(x, y);
            return mPoint;
        } else {
            return new PointF(x, y);
        }
    }
}