Drawing a transparent circle on top of a UIImage - iPhone SDK

Question

I am having a lot of trouble trying to find out how to draw a transparent circle on top of a UIImage within my UIImageView. Google-ing gives me clues, but I still can\'t find a

Answer 1

You can implement a custom sub-class of UIView that draws your image and then the circle in the drawRect method:

@interface CircleImageView : UIView {
    UIImage * m_image;
    CGRect m_viewRect;

    // anything else you need in this view?
} 

Implementation of drawRect:

- (void)drawRect:(CGRect)rect {

    // first draw the image
    [m_image drawInRect:m_viewRect blendMode:kCGBlendModeNormal alpha:1.0];

    // then use quartz to draw the circle
    CGContextRef context = UIGraphicsGetCurrentContext ()

    // stroke and fill black with a 0.5 alpha
    CGContextSetRGBStrokeColor(context, 1.0, 1.0, 1.0, 0.5);
    CGContextSetRGBFillColor(context, 1.0, 1.0, 1.0, 0.5);

    // now draw the circle
    CGContextFillEllipseInRect (context, m_viewRect);
}

You will need to set up the m_viewRect and m_image member functions on init.