Cocoa Programming for OS X: The Big Nerd Ranch Guide

Saving and Restoring the Graphics State

Recall that the graphics context manages the graphics state, which includes the current color, any transforms such as scaling or rotation, and so on. At times, it is convenient to treat the graphics state like a stack: You make a copy of the current state and push it onto the stack. Now the copy is the current state. You can alter the state, run some drawing commands, and then pop the state to return to the prior state.

To see this in action, let’s add a shadow to the die shown in DieView. AppKit shadows are configured using the NSShadow class. Update drawDieWithSize(_:):

 let dotRadius = edgeLength/12.0 let dotFrame = dieFrame.rectByInsetting(dx: dotRadius * 2.5, dy: dotRadius * 2.5) ...