samples/devbytes/animation/CurvedMotion/src/com/example/android/curvedmotion/PathEvaluator.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 com.example.android.curvedmotion;

import android.animation.TypeEvaluator;

/**
 * This evaluator interpolates between two PathPoint values given the value t, the
 * proportion traveled between those points. The value of the interpolation depends
 * on the operation specified by the endValue (the operation for the interval between
 * PathPoints is always specified by the end point of that interval).
 */
public class PathEvaluator implements TypeEvaluator<PathPoint> {
    @Override
    public PathPoint evaluate(float t, PathPoint startValue, PathPoint endValue) {
        float x, y;
        if (endValue.mOperation == PathPoint.CURVE) {
            float oneMinusT = 1 - t;
            x = oneMinusT * oneMinusT * oneMinusT * startValue.mX +
                    3 * oneMinusT * oneMinusT * t * endValue.mControl0X +
                    3 * oneMinusT * t * t * endValue.mControl1X +
                    t * t * t * endValue.mX;
            y = oneMinusT * oneMinusT * oneMinusT * startValue.mY +
                    3 * oneMinusT * oneMinusT * t * endValue.mControl0Y +
                    3 * oneMinusT * t * t * endValue.mControl1Y +
                    t * t * t * endValue.mY;
        } else if (endValue.mOperation == PathPoint.LINE) {
            x = startValue.mX + t * (endValue.mX - startValue.mX);
            y = startValue.mY + t * (endValue.mY - startValue.mY);
        } else {
            x = endValue.mX;
            y = endValue.mY;
        }
        return PathPoint.moveTo(x, y);
    }
}