Android贝塞尔曲线初步学习第三课 Android实现添加至购物车的运动轨迹

 @Override
 protected void onSizeChanged(int w, int h, int oldw, int oldh) {
 super.onSizeChanged(w, h, oldw, oldh);
 mStartX = 100;
 mStartY = 100;
 mEndX = w - 100;
 mEndY = h - 100;
 mControlX = w - 100;
 mControlY = 100;
 }

@Override
 protected void onDraw(Canvas canvas) {
 super.onDraw(canvas);
 canvas.drawCircle(mStartX, mStartY, 24, mCirclePaint);
 canvas.drawCircle(mEndX, mEndY, 24, mCirclePaint);
 mPath.reset();
 mPath.moveTo(mStartX, mStartY);
 mPath.quadTo(mControlX, mControlY, mEndX, mEndY);
 canvas.drawPath(mPath, mPathPaint);
 }

/**
 * 计算贝赛尔曲线坐标的工具类
 */

public class BezierUtil {
 /**
 * 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;
 }

 /**
 * 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;
 }
}

/**
 * 贝赛尔曲线估值器
 */
public class BezierEvaluator implements TypeEvaluator<PointF> {

 /* 控制点坐标 */
 private PointF mControlPoint;

 public BezierEvaluator(PointF controlPoint) {
 mControlPoint = controlPoint;
 }

 @Override
 public PointF evaluate(float v, PointF pointF, PointF t1) {
 return BezierUtil.calculateBezierPointForQuadratic(v, pointF, mControlPoint, t1);
 }
}

 @Override
 public void onClick(View view) {
 BezierEvaluator evaluator = new BezierEvaluator(new PointF(mControlX, mControlY));
 PointF startPoint = new PointF(mStartX, mStartY);
 PointF endPoint = new PointF(mEndX, mEndY);
 ValueAnimator anim = ValueAnimator.ofObject(evaluator, startPoint, endPoint);
 anim.setDuration(1000);
 anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
  @Override
  public void onAnimationUpdate(ValueAnimator valueAnimator) {
  PointF curPoint = (PointF) valueAnimator.getAnimatedValue();
  mCurX = (int) curPoint.x;
  mCurY = (int) curPoint.y;
  invalidate();
  }
 });
 anim.start();
 }

canvas.drawCircle(mCurX, mCurY, 24, mCirclePaint);