Editing Texture mapping (section)

====Screen space subdivision====
[[File:Texturemapping subdivision.svg|thumb|200 px|Screen space sub division techniques. Top left: Quake-like, top right: bilinear, bottom left: const-z]]

Software renderers generally preferred screen subdivision because it has less overhead. Additionally, they try to do linear interpolation along a line of pixels to simplify the set-up (compared to 2d affine interpolation) and thus again the overhead (also affine texture-mapping does not fit into the low number of registers of the [[x86]] CPU; the [[68000]] or any [[RISC]] is much more suited).

A different approach was taken for ''[[Quake (video game)|Quake]]'', which would calculate perspective correct coordinates only once every 16 pixels of a scanline and linearly interpolate between them, effectively running at the speed of linear interpolation because the perspective correct calculation runs in parallel on the co-processor.<ref>Abrash, Michael. ''Michael Abrash's Graphics Programming Black Book Special Edition.'' The Coriolis Group, Scottsdale Arizona, 1997. {{ISBN|1-57610-174-6}} ([http://www.gamedev.net/reference/articles/article1698.asp PDF] {{Webarchive|url=https://web.archive.org/web/20070311022026/http://www.gamedev.net/reference/articles/article1698.asp |date=2007-03-11 }}) (Chapter 70, pg. 1282)</ref> The polygons are rendered independently, hence it may be possible to switch between spans and columns or diagonal directions depending on the orientation of the [[polygon normal]] to achieve a more constant z but the effort seems not to be worth it.