Question

This is the code I have:

CGContextRef context = UIGraphicsGetCurrentContext();
    CGColorRef redColor = [UIColor colorWithRed:1.0 green:0.0 blue:0.0 alpha:1.0].CGColor;

CGRect rectangle = CGRectMake(100, 100, 100, 100);
    CGRect inside = CGRectMake(120, 120, 60, 60);



CGContextSetFillColorWithColor(context, redColor);
CGContextSetBlendMode(context, kCGBlendModeNormal);
CGContextFillRect(context, rectangle);
CGContextSaveGState(context);

CGContextSetBlendMode(context, kCGBlendModeSourceOut);
CGContextFillRect(context, inside);
CGContextRestoreGState(context);

I’m trying to make the inside shape hollow, but instead it’s giving me a red square (as expecetd) with a black square in the middle, when the UIView in the background is white.

Any ideas on how to make the shape transparent here?

Answer 1

There are a few ways you can fill your rectangle with a hollow inner rectangle. One way is to create a path that contains both rectangles, and fill it using the even-odd rule.

CGContextRef gc = UIGraphicsGetCurrentContext();
CGContextBeginPath(gc);
CGContextAddRect(gc, CGRectMake(100, 100, 100, 100));
CGContextAddRect(gc, CGRectMake(120, 120, 60, 60));
CGContextSetFillColorWithColor(gc, [UIColor redColor].CGColor);
CGContextEOFillPath(gc);