$lightwarptexture

The technique was first used in Day of Defeat: Source's snow maps, such as Kalt.

$lightwarptexture is a cornerstone of Team Fortress 2's illustrative character rendering.

Posterized color can be achieved, but lighting must be tightly controlled.

Template:Shaderparam It tints texels depending on their brightness. It can be thought of as localized color correction.

Important:$lightwarptexture must be specified after all other textures, otherwise it will overwrite them.

Important:$lightwarptexture on VertexLitGeneric requires a $bumpmap, not having one means a default one will used instead! This means that in practice, it will be like you did specify $bumpmap!

Note:Does not work without $phong on VertexLitGeneric in Counter-Strike: Source and CS:GO engine branch.

Note:$lightwarptexture does not seem to exist at all for LightmappedGeneric in CS:GO engine branch.

Bug:Does not work when using $detail or $bumpmap2 on both LightmappedGeneric and WorldVertexTransition.  [todo tested in ?]

Bug:Does not work when using $selfIllumFresnel without also using $phong.  [todo tested in ?]

Bug:Does not work when using $seamless_scale.  [todo tested in ?]

Lightwarp textures

A lightwarp texture is a one-dimensional strip of pixels. Dark texels will be tinted with the colour on the left-hand side, and bright texels with the colour on the right. 50% gray means no tint.

Examples

snow_warp

This is the lightwarp texture used in the Day of Defeat: Source screen to the right. It is designed to add a subtle bluish tint to darker snow without affecting brighter regions.

pyro_lightwarp

This is applied to all Team Fortress 2 characters, not just the Pyro. It creates the high-contrast shadows with red-tinged terminators typical of the illustrative art the game apes.

Posterized

This custom warp texture creates a posterized "line art" style. Enabling lightwarp alone isn't enough however: ambient lighting must be at 0 to make unlit areas black, and world lighting must become viewer-dependent to ensure that shadows are always cast.

Cel Shading

Cel shading can make objects look more cartoony by replacing the smooth lighting gradient with sharp steps.

Other possible uses of $lightwarptexture include contrast enhancement, tweaking vertex lighting shadow transitions, highlight softening, and more.

Cel shading in action.