How to compensate the flipped coordinate system of core graphics for easy drawing?

Question

It\'s really a pain, but always when I draw an UIImage in -drawRect:, it\'s upside-down.

When I flip the coordinates, the image draws correctly, but at the cost of a

Answer 1

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];
    UIGraphicsEndImageContext();
    return result;
}

Call the above method using the code below: This code deals with getting the left half of an image from an existing UIImageview and setting the thus generated image to a new imageview - imgViewleft

CGContextRef con = UIGraphicsGetCurrentContext();
CGContextDrawImage(con,  
                   CGRectMake(0,0,sz.width/2.0,sz.height),
                   flip(leftReference));
imgViewLeft = [[UIImageView alloc] initWithImage:UIGraphicsGetImageFromCurrentImageContext()];