Thanks for the shout-out! Though you might be disappointed, this is a Pong PCB, no relays to be found - http://www.crazykong.com/pcbs/P%20-%20S/Pong.pcb.jpg … - but if you have two counter ICs, you know the XY position of your raster beam. With that, you can compare against specific values, and so on... :-)
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As for how it's emulated in MAME, it uses the same sort of principle that programs like SPICE use to simulate mixed analog/digital circuits, only way faster! :-D