图形上下文

1. 开启图形上下文,指定尺寸,不透明,缩放参数为0,即根据当前屏幕自动缩放 UIGraphicsBeginImageContextWithOptions(image.size,NO,0);

2.描述裁剪路径

UIBezierPath*path = [UIBezierPathbezierPathWithOvalInRect:CGRectMake(0,0, image.size.width, image.size.height)];

3.设置裁剪区域

[path addClip];

4.绘图

[imagedrawAtPoint:CGPointZero];

5.获取绘制后的图片内容

image =UIGraphicsGetImageFromCurrentImageContext();

5.关闭上下文

UIGraphicsEndImageContext();