We want to get called for every display that intersects our window. SetEntries applies to the current GDevice, so make targetDevice the current GDevice. Insert the entire table into targetDevice. Do it in indexed mode. Restore the old current GDevice.
Users can change resolutions on multiple-scan displays.
Graphics mirroring could be off when the application is launched and turned on while it's running. Users can put their PowerBooks to sleep and attach or remove an external display. If your application doesn't respond to these changes, it might present an inconsistent interface to the user. For example, the MPW Shell used to cache the gdRect of the main display and pass it to SizeWindow and MoveWindow. So if users changed the resolution of a display, they couldn't grow or move windows beyond the previous size of the display.