this post was submitted on 29 Mar 2024
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[–] dual_sport_dork@lemmy.world 53 points 8 months ago (26 children)

OG Doom does not support (or need) hardware 3D acceleration. It's not a polygonal rendering engine.

Relatedly, and probably not to anyone's surprise, this is why it's so easy to port to various oddball pieces of hardware. If you have a CPU with enough clocks and memory to run all the calculations, you can get Doom to work since it renders entirely in software. In its original incarnation -- modern source ports have since worked around this -- it is nonsensical to run Doom at high frame rates anyhow because it has a locked 35 FPS frame rate, tied to the 70hz video mode it ran in. Running it faster would make it... faster.

(Quake can run in software rendering mode as well with no GPU, but in the OG DOS version only in 320x200 and at that rate I think any modern PC could run it well north of 60 FPS with no GPU acceleration at all.)

[–] Num10ck@lemmy.world 22 points 8 months ago (5 children)

OG Doom engine uses pre-built lookup tables for fixed point trigonometry. (table captures the full 360 degrees for sine and cosine with 10240 elements)

[–] DdCno1@kbin.social 12 points 8 months ago (4 children)

Tons of software did this for the longest time. Lookup tables have been a staple of home computing for as long as home computers have existed.

[–] barsoap@lemm.ee 4 points 8 months ago

And CPUs still do it to this day. Nasty, nasty maths involved in figuring out an optimal combination between lookup table size and refinement calculations because that output can't be approximate, it has to work how IEEE floats are supposed to work. Pure numerology.

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