Android贝塞尔曲线初步学习第一课

canvas.drawLine(float startX, float startY, float stopX, float stopY, @NonNull Paint paint) ;

path.quadTo(float x1, float y1, float x2, float y2);

path.cubicTo(float x1, float y1, float x2, float y2, float x3, float y3);

 @Override
 public boolean onTouchEvent(MotionEvent event) {
 switch (event.getAction()) {
 case MotionEvent.ACTION_MOVE:
 mControlX = event.getX();
 mControlY = event.getY();
 invalidate();
 break;
 }
 return true;
 }

 @Override
 protected void onDraw(Canvas canvas) {
 super.onDraw(canvas);
 canvas.drawCircle(mStartX, mStartY, 8, mLinePaint);
 canvas.drawText("起点", mStartX, mStartY, mLinePaint);
 canvas.drawCircle(mEndX, mEndY, 8, mLinePaint);
 canvas.drawText("终点", mEndX, mEndY, mLinePaint);
 canvas.drawCircle(mControlX, mControlY, 8, mLinePaint);
 canvas.drawText("控制点", mControlX, mControlY, mLinePaint);
 canvas.drawLine(mStartX, mStartY, mControlX, mControlY, mLinePaint);
 canvas.drawLine(mEndX, mEndY, mControlX, mControlY, mLinePaint);

 mBezierPath.reset();//因为不断重绘，path的路径也要重置，不然页面上会显示很多条线
 mBezierPath.moveTo(mStartX, mStartY);//移至起点
 mBezierPath.quadTo(mControlX, mControlY, mEndX, mEndY);//二阶贝塞尔曲线，传入控制点和终点坐标
 canvas.drawPath(mBezierPath, mBezierPaint);
 }

 case MotionEvent.ACTION_UP:
 ValueAnimator animX = ValueAnimator.ofFloat(mControlX, getWidth() / 2);
 animX.setDuration(500);
 animX.setInterpolator(new OvershootInterpolator());
 animX.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
 @Override
 public void onAnimationUpdate(ValueAnimator animation) {
 mControlX = (float) animation.getAnimatedValue();
 invalidate();
 }
 });
 animX.start();
 ValueAnimator animY = ValueAnimator.ofFloat(mControlY, getHeight() / 2);
 animY.setDuration(500);
 animY.setInterpolator(new OvershootInterpolator());
 animY.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
 @Override
 public void onAnimationUpdate(ValueAnimator animation) {
 mControlY = (float) animation.getAnimatedValue();
 invalidate();
 }
 });
 animY.start();
 break;

 private boolean mIsSecondPoint = false;

 @Override
 public boolean onTouchEvent(MotionEvent event) {
 switch (event.getAction() & MotionEvent.ACTION_MASK) {//多点触控
 case MotionEvent.ACTION_POINTER_DOWN:
 mIsSecondPoint = true;
 break;
 case MotionEvent.ACTION_POINTER_UP:
 mIsSecondPoint = false;
 break;
 case MotionEvent.ACTION_MOVE:
 mControlX1 = event.getX(0);//获取控制点1的横纵坐标
 mControlY1 = event.getY(0);
 if (mIsSecondPoint) {
  mControlX2 = event.getX(1);//获取控制点2的横纵坐标
  mControlY2 = event.getY(1);
 }
 invalidate();
 break;
 }
 return true;
 }

 mBezierPath.reset();
 mBezierPath.moveTo(mStartX, mStartY);
 mBezierPath.cubicTo(mControlX1, mControlY1, mControlX2, mControlY2, mEndX, mEndY);
 canvas.drawPath(mBezierPath, mBezierPaint);