How to set RGBA Color of a Pixel of an UIImage

Question

I am looking for a possibility to set (change) the RGBA color of a Pixel of an UIImage for my Iphone Application. (I actually want to implement some floodfill stuff)

So I need something like this:

-(void) setPixelColorOfImage: (UIImage*) img atXCord: (int) x atYCord: (int) y
withRedColor: (CGFloat) red blueColor: (CGFloat) blue greenColor: (CGFloat) green
alpha: (CGFloat) alpha  {

// need some code her

}

Because this method will be called quite often, it shouldn't be too slow.

Please help.

Answer 1

UIImage is not (externally) mutable, so you must copy, then edit, then convert to UIImage.

Copy

• create a CGBitmapContext
• draw the source image onto it

Edit

• get a hold of the context's pixel buffer
• mutate that pixel buffer

Convert to UIImage

• copy a CGImage representation of the context
• create a new UIImage from the CGImage

fwiw, the form can also be used on osx (using NSImage).