iOS UIView subclass, draw see-through text to background

Question

I want to draw text onto my subclass on UIView so that the text is cut out of the shape and the background behind the view shows through, just like in the OSX Mavericks logo

Answer 1

I actually figured out how to do it on my own surprisingly but @StatusReport's answer is completely valid and works as it stands now.

Here's how I did it:

-(void)drawRect:(CGRect)rect{
    CGContextRef context = UIGraphicsGetCurrentContext();
    [[UIColor darkGrayColor]setFill]; //this becomes the color of the alpha mask
    CGContextFillRect(context, rect);
    CGContextSaveState(context);
    [[UIColor whiteColor]setFill];
    //Have to flip the context since core graphics is done in cartesian coordinates
    CGContextTranslateCTM(context, 0, rect.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);
    [textToDraw drawInRect:rect withFont:[UIFont fontWithName:@"HelveticaNeue-Thin" size:40];
    CGContextRestoreGState(context);
    CGImageRef alphaMask = CGBitmapContextCreateImage(context);
    [[UIColor whiteColor]setFill];
    CGContextFillRect(context, rect);
    CGContextSaveGState(context);
    CGContentClipToMask(context, rect, alphaMask);
    [backgroundImage drawInRect:rect];
    CGContextRestoreGState(context);
    CGImageRelease(alphaMask);
}

- (void)setTextToDraw:(NSString*)text{
    if(text != textToDraw){
        textToDraw = text;
        [self setNeedsDisplay];
    }
}

I have an @synthesize declaration for textToDraw so I could override the setter and call [self setNeedsDisplay]. Not sure if that's totally necessary or not.

I'm sure this has some typos but I can assure you, the spell checked version runs just fine.