Android CornerPathEffect图形问题

Question

当我使用CornerPathEffect绘制路径时，

mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
    mPaint.setStrokeCap(Paint.Cap.ROUND);
    mPaint.setStrokeJoin(Paint.Join.ROUND);
    mPaint.setPathEffect(new CornerPathEffect(50));

有时出现故障。

通过绘制这三点可以得到它

mPath.moveTo(3041f/10000f * screen_width, 680f/10000f * screen_width);
mPath.lineTo(3075f/10000f * screen_width, 644f/10000f * screen_width);
mPath.lineTo(2729f/10000f * screen_width, 993f/10000f * screen_width);
invalidate();

有什么问题？