[bananaboy]

Yes, I played it at the time on both a 286 and a 386. You might be right, although you're describing an algorithm more like what Duke3d used rather than raycasting in that case. I was talking purely about raycasting. So it sounds like a misunderstanding on my part.

It's true that Carmack has said several times, including in the readme to the source release of Wolf3d [0], that a BSP-based renderer might be faster than raycasting. He used a BSP tree based renderer for the SNES port of Wolf3d because the CPU was even slower, so I suppose that answers it! There's also a note in the GEBB page 164 from Carmack where he says it was slower than "looping through a few long wall segments". [1]

Early alpha versions of DOOM used a sector-based rendering technique, maybe like what you're describing, which ultimately was too slow [2]][3]. Then Carmack switched to BSP trees after doing the Wolf3d SNES port.

I think it would be pretty interesting to implement the same game with both a raycasting approach and a BSP or Build-style portal/sector approach and compare performance on a 386. DOOM ran terribly on a 386 but it did a lot more than Wolf3d, so it's not a great comparison. Catacomb 3D didn't use raycasting (it used a wall span rendering techniqe) and ran better than Wolf3d on similar hardware, but it had a bunch of glitches. But Carmack says they were due to lack of experience rather than the technique itself.

Anyway thanks for challenging my assumptions. This'll go on my todo list!

[0] https://github.com/id-Software/wolf3d [1] https://fabiensanglard.net/b/gebbwolf3d.pdf [2] https://youtu.be/NnkCujnYNSo?t=1592 [3] https://doomwiki.org/wiki/Doom_rendering_engine

[ant6n]

Thank you for all the interesting references. I had almost forgotten about the BSP-SNES port.

I think they main concern when doing sectors + portals for a wolf3d-type 3d engine is how much word is done when 'stepping into' portals. basically it requires changing the clipping range [x0, x] of the portal, and quickly finding the next visible wall segment. the clipping could actually be done in 'angle space', not even using vectors. That is, wall edges/"vertices" should be represented as [angle,distance]. I have also been thinking about how much of that math pipeline could be done using specialized 8-bit values and LUTs.

I have been thinking about trying to get something running on very slow hardware, although at some point the problem is more drawing on the screen quickly, not the renderer.