title: How to get the device's scale factor?
body: <p>I've been using <code>UIGraphicsBeginImageContextWithOptions()</code> and I noticed that the last field in that method is a <code>scalefactor</code>. And the apple docs says, if I want to set it to 0.0, then it will use the default scale factor of the device's main screen. Is there a way to get that default scale factor via property or method?</p>