iOS- 裁剪图片

//大图片，这是原图
UIImage *img = [UIImage imageNamed:@"LuckyAstrology"];
UIImage *imgSelected = [UIImage imageNamed:@"LuckyAstrologyPressed"];
//从图片中裁剪对应星座的图片，因为图片有十二星座，现将其十二等分分别设给十二个button
CGFloat smallW = img.size.width / 12 * [UIScreen mainScreen].scale;//由于CGImageCreateWithImageInRect方法只认像素，所以乘以其屏幕的scale，在Retina屏上为2，否则为1
CGFloat smallH = img.size.height * [UIScreen mainScreen].scale;
for (int i = 0; i < 12; i++) {
//在这里自定义button，重写其下面方法，将其按钮图片居于中间
/*
- (CGRect)imageRectForContentRect:(CGRect)contentRect{
CGFloat imageW = 40;
CGFloat imageH = 47;
CGFloat imageX = (contentRect.size.width - imageW)/2;
CGFloat imageY = 20;
return CGRectMake(imageX, imageY, imageW, imageH);
}
*/

CLButton *btn = [CLButton buttonWithType:UIButtonTypeCustom];
CGRect smallRect = CGRectMake(smallW * i, 0, smallW, smallH);

// CGImageCreateWithImageInRect只认像素
CGImageRef smallImage = CGImageCreateWithImageInRect(img.CGImage, smallRect);//从方法名即可看出这是创建一个CGImage，前面参数是你原图的CGImage，后面是你的截取的大小
[btn setImage:[UIImage imageWithCGImage:smallImage] forState:UIControlStateNormal];

CGImageRef  smallImageSelected = CGImageCreateWithImageInRect(imgSelected.CGImage, smallRect);
[btn setImage:[UIImage imageWithCGImage:smallImageSelected] forState:UIControlStateNormal];

[btn setBackgroundImage:[UIImage imageNamed:@"LuckyRototeSelected"] forState:UIControlStateSelected];

btn.bounds = CGRectMake(0, 0, 68, 143);

//这里设置anchorPoint与position，根据其frame.origin.x = position.x-anchorPoint*btn.size.width从而确定其x,y点

btn.layer.anchorPoint = CGPointMake(0.5, 1);

btn.layer.position = CGPointMake(self.centerView.frame.size.width * 0.5, self.centerView.frame.size.height * 0.5);

//设置旋转角度（绕着锚点进行旋转）
CGFloat angle = (30 * i) / 180.0 * M_PI;

btn.transform = CGAffineTransformMakeRotation(angle);//将btn按某一个角度旋转，围成一个圆形

CADisplayLink *link = [CADisplayLink displayLinkWithTarget:self selector:@selector(refresh)];//这个方法一秒钟会刷新60帧，相当于调用60次方法
[link addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];