android 画日出日落圆弧曲线

    private PointF mPointF1;

    private PointF mControl;


    private PointF touchPoint;


    private float startAngle = 180;
    private float sweepAngle = 60;
    private float radius = 100;
    private float LEFT = 100;
    private float TOP = LEFT + radius;
    private float RIGHT = 300;
    private float BOTTOM = 400;
    private RectF mRectF;


    private void init() {
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setStyle(Paint.Style.FILL);
        mPaint.setColor(Color.BLACK);
        mPath = new Path();
        mPointF1 = new PointF(LEFT, RIGHT);
        touchPoint = new PointF(0,0);
        mControl = new PointF(0,0);
        mRectF = new RectF(LEFT,TOP,RIGHT,BOTTOM);
    }


    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_MOVE:
            case MotionEvent.ACTION_DOWN:
                touchPoint.x = event.getX();
                touchPoint.y = event.getY();
                float d = BOTTOM - radius - touchPoint.y;
                float l = touchPoint.x - LEFT - radius;
                Log.e("jyg","onTouchEvent,d="+d);
                Log.e("jyg","onTouchEvent,l="+l);
                float angle = (float)Math.toDegrees(Math.atan (d/l));
                Log.e("jyg","onTouchEvent,angle="+angle);
                if(angle < 0){
                    sweepAngle = Math.abs(angle);
                } else if(angle < 180){
                    sweepAngle = 180 - angle;
                }


                Log.e("jyg","onTouchEvent,touchPoint="+touchPoint);
                Log.e("jyg","onTouchEvent,sweepAngle="+sweepAngle);
                invalidate();
                break;


        }
        return true;
    }

    private Paint mPaint;
    private Path mPath;

    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        mPath.reset();
        draw1(canvas);
    }


    private void draw1(Canvas canvas) {
        mPath.moveTo(mPointF1.x, mPointF1.y);
        mPath.arcTo(mRectF,startAngle,sweepAngle);


        float xx,yy;
        xx = LEFT+radius - (float)(Math.cos(Math.toRadians(sweepAngle)) * radius);
        yy = BOTTOM - radius - (float) Math.sin(Math.toRadians(sweepAngle)) * radius;


        Log.e("jyg","xx="+xx);
        Log.e("jyg","yy="+yy);
        mControl.x = xx;
        mControl.y = yy;
        mPath.moveTo(mControl.x, mControl.y);
        mPath.lineTo(mControl.x,BOTTOM-radius);
        mPath.lineTo(mPointF1.x,mPointF1.y);
        canvas.drawPath(mPath, mPaint);
    }