Question

I have a png image like this:

How can I invert the frame around the waveform so it appears black, without changing the alpha of the waveform itself. (The waveform part is transparent.)

It probably has something to do with CGCreateImageMask but I can’t figure out the exact process.

Answer 1

Figured it out:

-(void)drawRect:(CGRect)rect {
    UIImage *wf = [UIImage imageNamed:@"waveform.png"];
    [wf drawInRect:rect blendMode:kCGBlendModeXOR alpha:1.0f];
}