Core graphics images low quality

Question

I'm the new one in Core Graphics and I try to draw circles. They can be transparent (only stroke) and filled with the stroke color. So the method looks like this:

+ (UIImage *)iconImageWithColor: (UIColor *)markColor strokeOnly:(BOOL)strokeOnly
{
    CGRect rect = CGRectMake(0.0f, 0.0f, 20.0f, 20.0f);

    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();

    CGPathRef clippingPath = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:7.5f].CGPath;
    CGContextAddPath(context, clippingPath);
    CGContextClip(context);

    CGContextSetFillColorWithColor(context, strokeOnly == YES ? [[UIColor clearColor] CGColor] : [markColor CGColor]);
    CGContextFillRect(context, rect);

    CGPathRef path = CGPathCreateWithRoundedRect(rect, 10.f, 10.f, NULL);
    [markColor setStroke];
    CGContextAddPath(context, path);
    CGContextDrawPath(context, kCGPathFillStroke);

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

    return image;
}

The result is strange - it looks like the resolution of the image is very low. Is it possible to make the result image looks good on retina display?

Answer 1

UIGraphicsBeginImageContext creates a context with a scale of 1, so non retina. What you want to use is

UIGraphicsBeginImageContextWithOptions(rect.size, NO, 0.0f)

scale 0 means it will use the device screen scale

Answer 2

Use UIGraphicsBeginImageContextWithOptions(rect.size, YES, 0.0);

Last parameter means the resulting pixel density (scale). When you pass 0 it picks it up automatically from device native screen scale.