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