将CGImageRef（不是UIImage）绘制到图像上下文中

Question

Here's exactly how to draw a UIImage in to context:

UIGraphicsBeginImageContextWithOptions(size, NO, 0.0f);
[someUIImage drawInRect:CGRectMake(...)];
[someOtherUIImage drawInRect:CGRectMake(...)];
[someOtherUIImage drawInRect:CGRectMake(...)];
UIImage *yourResult = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

No problem. However, say I have a CGImageRef which was built up somehow.

CGImageRef happyImageRef = CGImageCreateWithImageInRect(blah blah);

I want to draw it in to the context.

UIGraphicsBeginImageContextWithOptions(size, NO, 0.0f);
[ happyImageRef .. somehowDrawInRect:CGRectMake(...)];
UIImage *yourResult = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

How do you do that?

To be clear, obviously you can just convert it to a UIImage

UIImage *wasteful = [UIImage imageWithCGImage:happyImageRef];

But that seems incredibly inefficient. How to do it?

I'm sure I'm confused or missing something simple, so thanks.

Answer 1

Use CGContextDrawImage

UIGraphicsBeginImageContextWithOptions(size, NO, 0.0f);
CGContextDrawImage(UIGraphicsGetCurrentContext(),CGRectMake(...), happyImageRef);
UIImage *yourResult = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();