Combining Images with UIImage & CGContext – (Offscreen drawing)

Georg Tremmel — Wed, 20 Jan 2010 09:25:49 +0000

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();

Concatenating Strings @”string1″ @”string2″ @”stringN”

Georg Tremmel — Wed, 01 Apr 2009 06:44:27 +0000

That’s basically it.

No more
[@"string1" stringByAppendingString:@"string2"];

or
[NSString stringWithFormat:@"string1%@", @"string1"];

just
@"string1" @"string2" @"stringN" -> @"string1string2stringN"

The Objective-C 2.0 Programming Language.pdf, p131

Codec » combine

Combining Images with UIImage & CGContext – (Offscreen drawing)

Concatenating Strings @”string1″ @”string2″ @”stringN”