iOS如何將圖像的一部分繪製到特定的矩形？

Question

我想裁剪200 * 200的圖像，裁剪的部分是（x = 10，y = 10，w = 50，h = 50）。並繪製這部分新的500 * 500圖像，新矩形（x = 30，y = 30，w = 50，h = 50），該怎麼做？

我可以用下面的方法

- (UIImage*) getSubImageWithRect: (CGRect) rect { 

    UIGraphicsBeginImageContext(rect.size); 
    CGContextRef context = UIGraphicsGetCurrentContext(); 

    // translated rectangle for drawing sub image 
    CGRect drawRect = CGRectMake(-rect.origin.x, -rect.origin.y, self.size.width, self.size.height); 

    // clip to the bounds of the image context 
    // not strictly necessary as it will get clipped anyway? 
    CGContextClipToRect(context, CGRectMake(0, 0, rect.size.width, rect.size.height)); 

    // draw image 
    [self drawInRect:drawRect]; 
    // grab image 
    UIImage* subImage = UIGraphicsGetImageFromCurrentImageContext(); 

    UIGraphicsEndImageContext(); 

    return subImage; 
} 

Answer 1

讓我們嘗試使用下面的代碼塊

- (UIImage*) getSubImageFromImage:(UIImage *)image 
{ 
     // translated rectangle for drawing sub image 
     CGRect drawRect = CGRectMake(10, 10, 50, 50); 
     // Create Image Ref on Image 
     CGImageRef imageRef = CGImageCreateWithImageInRect([image CGImage], rect); 
     // Get Cropped Image 
     UIImage *img = [UIImage imageWithCGImage:imageRef]; 
     CGImageRelease(imageRef); 
     return img; 
}