Comment for last paragraph of "Drawing floors and ceilings" section - main reason for Doom drawing flats as horizontal strips is different. Every horizontal strip of a flat has the same depth in the scene, so entire strip uses the same texture scale. Drawing flats as vertical strips requires quite costly division by depth for every pixel and rendering speed would really suffer from it at the time. -- KrzysiekK

I've tried to make this clear in a revision. As an aside, the format of the flats has nothing to do with whether its easier to draw them horizontally or vertically. Because the player view can rotate, the texture needs to be traversed in arbitrary directions; up, down, left, right, and any angle even, as drawing moves across the span. Contrast with wall and sprite drawing, where moving down the screen is always moving down the texture. See (as in linuxdoom-1.10) r_draw.c, lines 489-564. The code begisn with some explanitory comments that are sort of what I just said, and the final do loop is the texture traversal at an arbitrary angle. 22:40, 16 September 2007 (UTC)