/vr/ - Retro Games

>>7497439
It's actually quite different, Doom uses what's called Binary Space Partitioning, which means you use a utility to construct a BSP tree (these days level editors have built in 'nodebuilders' but in the old days they were separate programs). The BSP tree is the level cut up into 'leaves' which means all the geometry is separated into pieces, so the game can determine what needs to rendered at what times and what not to. This means that the game will skip rendering almost all things which aren't in the player's view. It's not perfect to 100%, but it culls so much which wouldn't need to render that it works very well. This could also be exploited to have more detail in the level, if the map is constructed in such a way that you can never exceed the visplane limit (thus crashing the game) by simply not being able to see too many surfaces (or 'leaves') at once at any one time. In the early and mid 90s, you still couldn't go completely wild, as being right under the visplane limit would still make a 486 sweat bullets, and iD had to make sure none of their levels dipped too much for 386 computers, even if they had to run in Low Detail Mode and with reduced screen size, so no iD map is even close to the limit.

With the advent of ports like Boom, all the static limits were raised to effectively infinite levels, and by this time computers were getting stronger and stronger, so it stops being a matter of engine limits and instead turns towards what your CPU can calculate. Today, in the future, this can allow for quite complex levels with rather intricate detail.

Binary Space Partitioning predates John Carmack by a year, though he was the first guy to ever apply it to a commercial product like a videogame, to render three dimensional worlds in real time. The Quake games would also use it, as would Half-Life and then Half-Life 2, having their basis in a licensed Quake engine.