Cocoa Programming for OS X: The Big Nerd Ranch Guide

For the More Curious: Are You Drawing to the Screen?

In an application, you will often want to draw things differently on screen than on the printer. For example, in a drawing program, the on-screen view might show a grid on-screen but not when printed on paper.

In your drawRect(_:) method, you can ask the current graphics context if it is currently drawing to the screen:

if NSGraphicsContext.currentContextDrawingToScreen() {
    // ... draw the grid ...
}