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0 pointsSohcahtoa822mo ago0 comments

I often think about DOOM running on a 66 Mhz 486.

It ran at around 30 fps with a 320x200 screen. That's 64,000 pixels per frame, 1,920,000 pixels per second being rendered.

On a 66 Mhz CPU, that means less than 35 clock cycles per pixel, on a CPU architecture where a multiply or add instruction would take multiple clock cycles to complete.

I know DOOM was not a true 3D engine and it took a lot of shortcuts to look the way it did, but that makes it more amazing, not less. The amount of thought to go into it is just mind-boggling to me.

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2 comments · 1 top-level

cogman102mo ago· 1 in thread

> multiply or add instruction would take multiple clock cycles.

Add, and, or, xor, and bit shift have always been single cycle operations for integers. Doom used integer math for everything I believe.

Sohcahtoa82OP2mo ago

Ah, so you're right.

Still though...care had to be taken to make sure memory was organized to maximize cache hits.

I feel like the crazy optimizations necessary in those days have become a lost art to most game developers.

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