XMG 中间透明。四周不透明的蒙版

- (void)drawRect:(CGRect)rect {

CGFloat w=rect.size.width;

CGFloat h=rect.size.height;

// int radius = rect.size.width/2.0;

CGFloat currentW=w-100;

CGFloat currentH=h-100;

CGFloat currentX=50;

CGFloat currentY=50;

CGRect rect1=CGRectMake(currentX, currentY, currentW, currentH);

UIBezierPath*path=[UIBezierPath
bezierPathWithRect:rect];

UIBezierPath*path2=[UIBezierPath
bezierPathWithRect:rect1];

[path appendPath:path2];

[path setUsesEvenOddFillRule:YES];

CAShapeLayer *fillLayer = [CAShapeLayer
layer];

fillLayer.path = path.CGPath;

fillLayer.fillRule =kCAFillRuleEvenOdd;

fillLayer.fillColor = [UIColor
grayColor].CGColor;

fillLayer.opacity =1;

[self.layer
addSublayer:fillLayer];

}