iOS开发探索-图形剪切实践总结

一、通过UIImageView的layer的属性，实现把图像显示成圆角，而无需对图像本身进行处理。在开发中，大部分情况下，我们只需要“显示”圆角，而不是“得到”圆角图像。

imageView.layer.cornerRadius = 100;
imageView.layer.masksToBounds = YES;

**注意: **每个UIView对象都有一个layer属性，这个layer属性实际上是一个CALayer对象, 该对象负责图形的渲染显示。并且layer有一个cornerRadius属性，用来指定layer的边框圆角。其中layer默认显示超出边框的图像，所以必须指定masksToBounds属性为YES，使得layer切掉边框外的部分。

二、剪切图片让图片圆形展示
方案一:
- (UIImage *)roundedCornerImageWithCornerRadius:(CGFloat)radius
{
CGFloat w = self.size.width;
CGFloat h = self.size.height;
CGFloat scale = [UIScreen mainScreen].scale;
if (radius < 0) {
radius = 0;
}else if(radius > MIN(w, h)){
radius = MIN(w, h)/2.0;
}
UIImage *image = nil;
CGRect imageFrame = CGRectMake(0, 0, w, h);
UIGraphicsBeginImageContextWithOptions(self.size, NO, scale);
[[UIBezierPath bezierPathWithRoundedRect:imageFrame cornerRadius:radius] addClip];
[self drawInRect:imageFrame];
image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}

方案二:
- (UIImage*)imageByRoundCornerRadius:(CGFloat)radius
{
UIGraphicsBeginImageContext(self.size);
CGContextRef gc = UIGraphicsGetCurrentContext();

    float x1 = 0.;
    float y1 = 0.;
    float x2 = x1+self.size.width;
    float y2 = y1;
    float x3 = x2;
    float y3 = y1+self.size.height;
    float x4 = x1;
    float y4 = y3;
    radius = radius*2;

    CGContextMoveToPoint(gc, x1, y1+radius);
    CGContextAddArcToPoint(gc, x1, y1, x1+radius, y1, radius);
    CGContextAddArcToPoint(gc, x2, y2, x2, y2+radius, radius);
    CGContextAddArcToPoint(gc, x3, y3, x3-radius, y3, radius);
    CGContextAddArcToPoint(gc, x4, y4, x4, y4-radius, radius);

    CGContextClosePath(gc);
    CGContextClip(gc);

    CGContextTranslateCTM(gc, 0, self.size.height);
    CGContextScaleCTM(gc, 1, -1);
    CGContextDrawImage(gc, CGRectMake(0, 0, self.size.width, self.size.height), self.CGImage);

    UIImage *newimage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return newimage;
} 

示例图片

参考Demo:https://github.com/524429264/CornerImage

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