Retina display core graphics font quality

问题:

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

The letter "W" is drawn using CGContextShowTextAtPoint on a CALayer and looks very pixelized. The button next to it is a standard button and looks high res as expected. I would like to get the text drawing to be hi-res.

回答1:

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.

回答2:

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);

回答3:

A group of functions controls how Core Graphics renders fonts:

• CGContextSetAllowsAntialiasing
• CGContextSetAllowsFontSmoothing
• CGContextSetAllowsFontSubpixelPositioning
• CGContextSetAllowsFontSubpixelQuantization

回答4:

Swift version:

textLayer.contentsScale = UIScreen.mainScreen().scale