Android 贝塞尔曲线获取运动轨迹_Android

Android 贝塞尔曲线获取运动轨迹

BezierUtil辅助类

package demo.ht.com.utils;

import android.graphics.PointF;

public class BezierUtil {

    /**
     * 二阶贝塞尔曲线B(t) = (1 - t)^2 * P0 + 2t * (1 - t) * P1 + t^2 * P2, t ∈ [0,1]
     *
     * @param t  曲线长度比例
     * @param p0 起始点
     * @param p1 控制点
     * @param p2 终止点
     * @return t对应的点
     */
    public static PointF CalculateBezierPointForQuadratic(float t, PointF p0, PointF p1, PointF p2) {
        PointF point = new PointF();
        float temp = 1 - t;
        point.x = temp * temp * p0.x + 2 * t * temp * p1.x + t * t * p2.x;
        point.y = temp * temp * p0.y + 2 * t * temp * p1.y + t * t * p2.y;
        return point;
    }

    /**
     * 三阶贝塞尔曲线B(t) = P0 * (1-t)^3 + 3 * P1 * t * (1-t)^2 + 3 * P2 * t^2 * (1-t) + P3 * t^3, t ∈ [0,1]
     *
     * @param t  曲线长度比例
     * @param p0 起始点
     * @param p1 控制点1
     * @param p2 控制点2
     * @param p3 终止点
     * @return t对应的点
     */
    public static PointF CalculateBezierPointForCubic(float t, PointF p0, PointF p1, PointF p2, PointF p3) {
        PointF point = new PointF();
        float temp = 1 - t;
        point.x = p0.x * temp * temp * temp + 3 * p1.x * t * temp * temp + 3 * p2.x * t * t * temp + p3.x * t * t * t;
        point.y = p0.y * temp * temp * temp + 3 * p1.y * t * temp * temp + 3 * p2.y * t * t * temp + p3.y * t * t * t;
        return point;
    }
}

自定义BezierEvaluator

package demo.ht.com.utils;

import android.animation.TypeEvaluator;
import android.graphics.PointF;

public class BezierEvaluator implements TypeEvaluator<PointF> {

    private PointF pointF1;
    private PointF pointF2;

	//传递的是控制点1 和控制点2
    public BezierEvaluator(PointF pointF1,PointF pointF2) {
        this.pointF1 = pointF1;
        this. pointF2 = pointF2;
    }

    @Override
    public PointF evaluate(float v, PointF pointF, PointF t1) {
    //这里用的是三阶贝塞尔曲线
     /**
     * @param t  曲线长度比例
     * @param p0 起始点
     * @param p1 控制点1
     * @param p2 控制点2
     * @param p3 终止点
     * @return t对应的点
     */
        return BezierUtil.CalculateBezierPointForCubic(v, pointF, pointF1, pointF2,t1);
    }
}

ValueAnimator动画

 private void initAnimation() {
        //创建贝塞尔曲线坐标的换算类                                 //x1y1是控制点1      x2,y2是控制点2
        BezierEvaluator evaluator = new BezierEvaluator(new PointF(x1, y1),new PointF(x2,y2));
        //指定动画移动轨迹
        ValueAnimator animator = ValueAnimator.ofObject(evaluator,
                new PointF(x0, y0),//起始点
                new PointF(x3, y3));//结束点
        animator.setDuration(600);
        animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator valueAnimator) {
                //改变小球坐标，产生运动效果
                PointF pointF = (PointF) valueAnimator.getAnimatedValue();
                /**
                 * mMovePointX 是最终贝塞尔曲线x坐标
                 * mMovePointY是最终贝塞尔曲线y坐标 
                 */
                mMovePointX = (int) pointF.x;
                mMovePointY = (int) pointF.y;
                //刷新UI
                invalidate();
            }
        });
        //添加加速插值器，模拟真实物理效果
        animator.setInterpolator(new AccelerateDecelerateInterpolator());
        animator.start();
    }