Inside Macintosh: Imaging with QuickDraw
Before drawing into the offscreen graphics port created in Listing 6-1 , MyPaintRectsThruGWorld saves the graphics port for the front window by calling the GetGWorld procedure, which saves the current graphics port and its GDevice record. Then MyPaintRectsThruGWorld makes the offscreen graphics world the current port by calling the SetGWorld procedure. After drawing into the offscreen graphics world, MyPaintRectsThruGWorld also uses SetGWorld to restore the active window as the current graphics port.
Instead of using the GetPort and SetPort procedures for saving and restoring offscreen graphics worlds, you must use GetGWorld and SetGWorld ; you can also use GetGWorld and SetGWorld for saving and restoring color and basic graphics ports.