Question

I have a few UIImage objects which I want to compose into a single UIImage and then save it to disk. I’m not displaying this on the screen so it doesn’t make sense to do it in -drawRect.

Is there a way of creating a context similar like in -drawRect: and then just draw the UIImage objects in there using something like CGContextDrawImage(context, imgRect, img.CGImage); ?

Answer 1

I believe you want to use a CGContextRef to draw all the images in at the desired place and then get the resulting image. The code will look something like this:

CGContextRef context = CGBitmapContextCreate(nil, desired_width, desired_height, bitsPerComponent, bytesPerRow, CGColorSpaceCreateDeviceRGB(), CGImageGetBitmapInfo(image));
//This code is to ilustrate what you have to do:
for(image in your Images) {

    CGContextDrawImage(context, CGRectMake(currentImage.frame.origin.x, currentImage.frame.origin.y, CGImageGetWidth(currentImage), CGImageGetHeight(currentImage), currentImage);
}

CGImageRef mergeResult  = CGBitmapContextCreateImage(context);

mergedImage = [[UIImage alloc] initWithCGImage:mergeResult];
CGContextRelease(context);
CGImageRelease(mergeResult);