//0.加載要裁剪的圖片

UIImage * image = [UIImage imageNamed:@"dst2"];

//1.開啟一個圖形上下文對象 (圖片類型 bitmap) 大小個圖片一樣大

//? ? UIGraphicsBeginImageContext(<#CGSize size#>)

//參數1:大小? 參數2:是否不透明 參數3:縮放比

UIGraphicsBeginImageContextWithOptions(image.size, NO, 0.0);//0.0使用當前設備的縮放比

//2.獲取剛剛開啟的圖形上下文對象

CGContextRef ctx = UIGraphicsGetCurrentContext();

//3.創建圓形路徑

//3.1 計算圓心 (圖片中心點)

CGPoint centerP = CGPointMake(image.size.width/2, image.size.height/2);

//3.2 計算半徑 (圖片最小邊的一半)

CGFloat radius = MIN(image.size.width, image.size.height)/2;

UIBezierPath * path = [UIBezierPath bezierPathWithArcCenter:centerP radius:radius startAngle:0 endAngle:2 * M_PI clockwise:YES];

//4.添加 路徑

CGContextAddPath(ctx, path.CGPath);

//5.執行裁剪

CGContextClip(ctx);

//6.繪制圖片

[image drawAtPoint:CGPointZero];

//7.從圖形上下文中獲取圖片

UIImage * getImage = UIGraphicsGetImageFromCurrentImageContext();

//7.1----------切割圖片----------------------

//? ? 計算 x y w g

CGFloat x = 0;

CGFloat y = (image.size.height - 2 * radius) / 2;

CGFloat w = 2 * radius;

CGFloat h = w;

//獲取當前設備的縮放比

CGFloat scale = [UIScreen mainScreen].scale;

x *= scale;

y = y * scale;

w *= scale;

h *= scale;

//參數1:要切割的圖片? 參數2:切割區域

CGImageRef imageRef = CGImageCreateWithImageInRect(getImage.CGImage, CGRectMake(x, y, w, h));

// CGImageRef-->UIImage

getImage = [UIImage imageWithCGImage:imageRef];

//7.1----------切割圖片----------------------

//8.結束圖形上下文對象

UIGraphicsEndImageContext();

//9.使用圖片

self.imageView.image = getImage;

//9.1 保存相冊

//參數1:保存的圖片? 參數2:調用哪個類的方法? 參數3:保存完畢要調用哪個方法? 參數4:追蹤信息

UIImageWriteToSavedPhotosAlbum(getImage, self, @selector(image:didFinishSavingWithError:contextInfo:), @"hello");

//9.2 保存到沙盒

//獲取documents

NSString * docDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];

//拼接文件名

NSString * fileName = [docDir stringByAppendingPathComponent:@"001.png"];

//轉化Data

NSData * imageData = UIImagePNGRepresentation(getImage);

//保存

[imageData writeToFile:fileName atomically:YES];