Question

A CALayer can do it, and a UIImageView can do it. Can I directly display an image with aspect-fit with Core Graphics? The UIImage drawInRect does not allow me to set the resize mechanism.

Answer 1

You need to do the math yourself. For example:

// desired maximum width/height of your image
UIImage *image = self.imageToDraw;
CGRect imageRect = CGRectMake(10, 10, 42, 42); // desired x/y coords, with maximum width/height

// calculate resize ratio, and apply to rect
CGFloat ratio = MIN(imageRect.size.width / image.size.width, imageRect.size.height / image.size.height);
imageRect.size.width = imageRect.size.width * ratio;
imageRect.size.height = imageRect.size.height * ratio;

// draw the image
CGContextDrawImage(context, imageRect, image.CGImage);

Alternatively, you can embed a UIImageView as a subview of your view, which gives you easy to use options for this. For similar ease of use but better performance, you can embed a layer containing the image in your view’s layer. Either of these approaches would be worthy of a separate question, if you choose to go down that route.