BezierPath 使用（1）-- 绘制圆角

 UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:portrait.bounds byRoundingCorners:UIRectCornerBottomLeft | UIRectCornerTopRight cornerRadii:CGSizeMake(20, 20)];

    CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];

    maskLayer.frame = portrait.bounds;

    maskLayer.path = maskPath.CGPath;

    portrait.layer.mask = maskLayer;

    [maskLayer release];