iOS局部透明 贝塞尔曲线

UIView *vi = [[UIView alloc] initWithFrame:frame];

vi.backgroundColor= [[UIColor blackColor] colorWithAlphaComponent:0.7];

UIBezierPath *path = [UIBezierPath bezierPathWithRect:vi.frame];
// 局部透明的rect
CGRect rect =  CGRectMake(0, 0, 100, 100);
[path appendPath:[[UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:rect.size.height / 2.0] bezierPathByReversingPath]];

CAShapeLayer *shapeLayer = [CAShapeLayer layer];

shapeLayer.path= path.CGPath;

[vi.layer setMask:shapeLayer];

[self.view addSubview:vi];