Retina display core graphics font quality

Question

Trying to understand why am I getting low quality drawing with CGContextShowTextAtPoint? See attached image:

Answer 1

Does using CGContextScaleCTM deliver any results for you? When working with a graphics context, something like this:

CGFloat scale = [[UIScreen mainScreen] scale];
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextScaleCTM(context, scale, scale);

Answer 2

By default, your CALayer is not rendering its Quartz content at the higher resolution of the Retina display screen. You can enable this using code like the following:

if ([layer respondsToSelector:@selector(setContentsScale:)])
{
    layer.contentsScale = [[UIScreen mainScreen] scale];
}

This will affect not just text rendering, but all of your Quartz drawing within CALayers, so you'll need to do this for all of your layers with custom Quartz content.

Answer 3

Swift version:

textLayer.contentsScale = UIScreen.mainScreen().scale

Answer 4

A group of functions controls how Core Graphics renders fonts:

• CGContextSetAllowsAntialiasing
• CGContextSetAllowsFontSmoothing
• CGContextSetAllowsFontSubpixelPositioning
• CGContextSetAllowsFontSubpixelQuantization