How to clear circle in CGContext in iOS

问题

I want create image using CGcontext. This is simple image with white or black background. also I want to add transperent part which is in circle ( check attached image). I know how to do this in rect. But i want to make it circle. Please anyone help me in this.

回答1:

Use the below code to clear circle in your context

-(UIImage *) getImageWithcenterClear:(CGPoint) center{

    CGRect frame = [[UIScreen mainScreen] bounds];

    UIGraphicsBeginImageContextWithOptions([[UIScreen mainScreen] bounds].size,
                                       NO, [UIScreen mainScreen].scale);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetFillColorWithColor(context, [[UIColor colorWithRed:0 green:0 blue:0 alpha:0.5 ] CGColor]);
    CGContextFillRect(context, frame);

    float radius = 50 * 2;
    // Clear Circle

    CGContextSetFillColorWithColor(context, [UIColor clearColor].CGColor);
    CGContextSetBlendMode(context, kCGBlendModeClear);
    CGContextAddArc(context, center.x, center.y, radius - 0.54, 0, 2 * M_PI, 0);
    CGContextDrawPath(context, kCGPathFill);
    CGContextSetBlendMode(context, kCGBlendModeNormal);

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return image;

}

来源：https://stackoverflow.com/questions/33580519/how-to-clear-circle-in-cgcontext-in-ios