Avoid getting repeated tick timers when restarting main loop

[epeld]

Hello!

I've run into an issue where tick-events fire on my glut windows once for every time I've entered glutMainLoop.

The reason seems to be that there is no way to cancel glut timers so they persist when leaving the main loop. Old timers stick around inside glut until the main loop is entered again. Since the main window always gets the same id (== 1), both old and new tick timers will have the same window id so they will all fire the window's tick-callback.

I was running SBCL on a Mac when I saw this.

I solved the issue by giving each tick-timer a unique id and providing an indirection through a lookup table from tick-timer-id to window-id. That way, I can clear out a window's tick timers by just removing its entries from the lookup table.

Another approach that I guess would work equally as well is to give each window a unique id.

Hope this makes sense.