Doom wasn't 3D!

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Re: Doom wasn't 3D!

Post by joefish » Fri Oct 21, 2016 6:17 am

Suprisingly raycasting does one thing that a lot of shortcut methods don't - it does actually give you perspective-correct textures on the walls. It's because of the way that the 'rays' - the lines being tracked - spread out with distance from the viewer, so will hit a wall texture further apart over distance. And incrementally further apart if the wall is slanted away from you.

Doing the walls with simple textured polygons, like those in the Playstation version of Quake, aren't corrected for perspective; they're just squashed and distorted into the 2D space the triangle ends up occupying on the screen. This was what let to those terrible warping visuals on Playstation games; if a square on the wall was split into two triangles, the top half would require a different distortion to the bottom half, so lines in the texture would slant one way in the top half and a different way in the bottom half. Some tried to get round this by chopping a square into four triangles, which is better, but still not perfect.

On the PC, both Quake and Descent could do (approximately) perspective-adjusted textures in their software rendering, but only by turning up the detail levels. At the basic levels it was just flat texturing. With early graphics cards too, it depended how much you were willing to spend.

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