334Combining Images with UIImage & CGContext – (Offscreen drawing)
In Cocoa NSImage has a lockFocus method, that allows to draw images offscreen and combine them into one.
[img lockFocus];
//...
[img unlockFocus];
On the iPhone, UIImage lacks the lockFocus methods, instead the following:
// Create new offscreen context with desired size
UIGraphicsBeginImageContext(CGSizeMake(64.0f, 64.0f));
// draw img at 0,0 in the context
[img drawAtPoint:CGPointZero];
// draw another at 0,0 in the context, maybe with an alpha value
[another drawAtPoint:CGPointZero];
// ... and other operations
// assign context to UIImage
UIImage *outputImg = UIGraphicsGetImageFromCurrentImageContext();
// end context
UIGraphicsEndImageContext();