iOS 繪圖 剪裁 oc UIGraphics

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
//    self.view.backgroundColor = [UIColor redColor];
    CGRect *rect;
    UIViewSon *son = [[UIViewSon alloc]init];
    [son drawRect:rect];
    
    UIImage  * tree = [UIImage imageNamed:@"hehe"];
    CGSize ts = [tree size];
    //使用uiimage進行繪圖
//    UIGraphicsBeginImageContextWithOptions(CGSizeMake(ts.width * 2,ts.height), NO, 0);
//    [tree drawAtPoint:CGPointMake(0, 0)];
//    [tree drawAtPoint:CGPointMake(ts.width, 0)];
//    UIImage *im = UIGraphicsGetImageFromCurrentImageContext();
//    UIGraphicsEndImageContext();
//    
//   
//    UIImageView *imv = [[UIImageView alloc]initWithImage:im];
//    [self.view addSubview:imv];
//    imv.center = self.view.center;
//    
    
    
    
    
    
    
    //使用CGImage進行繪圖
    
    /*
    //抽取圖片的左右兩邊
    CGImageRef marLeft = CGImageCreateWithImageInRect([tree CGImage], CGRectMake(0, 0, ts.width / 2, ts.height));
    CGImageRef marRight = CGImageCreateWithImageInRect([tree CGImage], CGRectMake(ts.width / 2, 0, ts.width / 2, ts.height));
    //將圖片繪製到畫布上去
    
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(ts.width * 1.5, ts.height), NO, 0);
    
    CGContextRef con = UIGraphicsGetCurrentContext();
    
    CGContextDrawImage(con, CGRectMake(0, 0, ts.width / 2, ts.height), flip(marLeft));
    
    CGContextDrawImage(con, CGRectMake(ts.width / 2, 0, ts.width / 2, ts.height), flip(marRight));
    
    UIImage * im = UIGraphicsGetImageFromCurrentImageContext();
    
    UIGraphicsEndImageContext();
    
    //釋放內存。arc在這裏無效
    CGImageRelease(marRight);
    CGImageRelease(marLeft);
    UIImageView *imv = [[UIImageView alloc]initWithImage:im];
    [self.view addSubview:imv];
    imv.center = self.view.center;
    
    //繪出來的圖是上下顛倒的，這不是你的問題，CGContextDrawImage來繪圖就會出現這種問題，這主要是由於原始的本地座標系與目標上下文不匹配
     1.解決方法是如此的奇葩。將CGImage 用CGContextDrawImage繪製到UIImage上，而後再獲取對應的CGImage，而後再將CGImage繪製到畫布上
    

    */
    
    /*你覺得這樣就完了？？？？那你就太天真了，如今又出現了另外一個問題：在雙分辨率的設備上，若是咱們的圖片文件是高分辨率（@2x）版本，上面的繪圖就是錯誤的。緣由在於對於UIImage來講，在加載原始圖片時使用的imageNamed：方法，它會自動根據所在設備的分辨率類型選擇圖片，而且UIImage經過設置用來適配的scale屬性補償圖片的兩倍尺寸。可是一個CGImage對象並無scale屬性，它不知道圖片文件的尺寸是否爲兩倍！因此當調用UIImage的CGImage方法，你不能假定所得到的CGImage尺寸與原始UIImage是同樣的。在單分辨率和雙分辨率下，一個UIImage對象的size屬性值都是同樣的，可是雙分辨率UIImage對應的CGImage是單分辨率UIImage對應的CGImage的兩倍大。因此咱們須要修改上面的代碼，讓其在單雙分辨率下均可以工做。代碼以下*/
    
    UIImage *mar = [UIImage imageNamed:@"hehe"];
    
    CGSize ms = [mar size];
    
    CGImageRef marCG = [mar CGImage];
    CGSize msCG = CGSizeMake(CGImageGetWidth(marCG), CGImageGetHeight(marCG));
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(ms.width, ms.height), NO, 0);
    CGImageRef imgLeft = CGImageCreateWithImageInRect(marCG, CGRectMake(0, 0, msCG.width / 2, msCG.height));
    CGImageRef imgRight = CGImageCreateWithImageInRect(marCG, CGRectMake(msCG.width / 2, 0, msCG.width / 2, msCG.height));
    
    [[UIImage imageWithCGImage:imgLeft scale:[mar scale] orientation:UIImageOrientationUp] drawAtPoint:CGPointMake(0, 0)];
    [[UIImage imageWithCGImage:imgRight scale:[mar scale] orientation:UIImageOrientationUp] drawAtPoint:CGPointMake(msCG.width / 2, 0)];

    UIImage * img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    //釋放內存。arc在這裏無效
    CGImageRelease(imgLeft);
    CGImageRelease(imgRight);
    UIImageView *imv = [[UIImageView alloc]initWithImage:img];
    [self.view addSubview:imv];
    imv.center = self.view.center;
    
}


//寫一個方法獲取圖片畫布，並將圖片先反轉繪製在畫布上
CGImageRef flip(CGImageRef im)
{
    CGSize sz = CGSizeMake(CGImageGetWidth(im), CGImageGetHeight(im));
    UIGraphicsBeginImageContextWithOptions(sz, NO, 0);
    CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, sz.width, sz.height), im);
    CGImageRef result = [UIGraphicsGetImageFromCurrentImageContext() CGImage];
    return result;
}



/*     CIFilter與CIImage。   */




- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


@end

這只是圖片剪裁的一部分

 

 

更多UIView繪圖參考http://www.cocoachina.com/industry/20140115/7703.html