需求要做個(gè)橢圓形的鏤空的蒙版，因?yàn)樵O(shè)計(jì)不在徽缚，只好自己繪制。
//自定義的一個(gè)View,添加到window上。self為自定義的View
//貝塞爾曲線 整個(gè)屏幕
UIBezierPath *bpath = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(0, 0, ScreenWidth, ScreenHeight) cornerRadius:0];
//貝塞爾曲線 畫一個(gè)橢圓
[bpath appendPath:[UIBezierPath bezierPathWithOvalInRect:CGRectMake(0, self.topOffset, self.maskWidth, self.maskHeight)].bezierPathByReversingPath];
//創(chuàng)建一個(gè)CAShapeLayer 圖層
CAShapeLayer *shapeLayer = [CAShapeLayer layer];
shapeLayer.path = bpath.CGPath;
//添加圖層蒙板
self.layer.mask = shapeLayer;
