Tool Textures
(More than just something to look at)
SKY
used for sky environments. can give off light when a light environment entity is used and ALL sides of the brush are covered with SKY. SKY does not create wpolys, so SKY generally cause less lag than regular {invisible textured brush faces. Does not block VIS.
problems = if zoner's compiling tools are not used, then mapper must block off sky with CLIP, or players can "Get out of map". Transparent within a map, will not block VIS inside a map, or between 2 map sections. SKY does not create wpolys, it is rendered in a manner similar to sprites, and so like sprites one can only measure the lag caused by the fps(frames per second).
Rad/Light Textures
, these give off light, but ONLY if listed with correct data in the lights.rad file or mapname.rad file. Supposedly it can be made switchable using a +A prefixed texture name, in the same way as Switchable Animating textures above. Other textures, like animated or regular, can also give off light if listed in lights.rad file.
problems = bad compiles stop lights from working. Too many different light types (8) shining on any brush cause compile crash. Memory used is the square of the number of lights on a brush face, 4 light types = 16 times the memory usage of 1 light type on a brush face - for EACH brush. But 8 identical lights do not cause a problem.
Masked/Transparent Textures
this is used for invisible, or semi-transparent textures, like ladders. It needs to be used with an entity like func wall or func illusionary with solid mode and fx set at 255. Texture for transparent part must be 0 0 255 blue, in Wally palette position #255. It must be entity, cannot block VIS.
problems = this texture is often made incorrectly, or set up incorrectly with the entity - be careful! Even totally invisible textures still make wpolys. ALL sides of a brush should be the same texture, although SKY or {invisible can sometimes cover a thin face or two.
alpha1.jpgalpha2.jpg
Liquid/Water
if this texture covers a brush then the engine assumes it is liquid and treats it like such. If you would like it see-thru, then you have to tie to entity func water and set the flags. Does not block VIS in any way.
problems = ALL sides of a brush should be the same water texture, or a compile problem or game problem may occur.
AAATRIGGER
used to help mappers visualize invisible brush entities, like triggers. It is usually invisible, but should NOT be used as a regular texture - it causes a compile problems and lighting problems. It MUST be an entity so it does not block VIS.
problems = if visible causes compile problems, and causes lighting problems along with odd scrolling & resizes in map, and can make HL & mods crash. Keep it invisible in an entity.
aaa.jpg
ORIGIN
used to denote the axis of swinging platforms & rotating fans, hinges of rotating doors, track connection of trains, ground connection of vehicles, and pivots of pendulums. Must be part of an entity. Invisible, does not block VIS.
problems = if alone in map, or if more than one ORIGIN used per entity, then it causes compile crash; ALL sides of a brush must be ORIGIN, no mixing textures allowed.
Switchable Animating
like regular animating above, except there is one texture of +A. if the brush involved is made a named func wall or other entity, then a trigger can target it and switch from the animation to the "stopped" +A texture.
problems = as regular animation. Also MUST be an entity, therefore it never blocks VIS.
Regular Animating
(+0 to +9) if +0texturename is used on a brush, then the animated series up to +9 will continuously "play" on the brush. Waterfall is an animated texture that should be tied to func water. May or may not block VIS depending on usage.
problems = if a texture whose name starts with +1 to +9 is used on a brush, then no animation, only that texture is shown. Textures must combine well, and fit brush.
ana.jpg
HINT/SKIP
a pair of textures of limited use, to split VIS leaf/portals so that line-of-sight & r_speeds can be reduced in some situations. Invisible, transparent, do not make wpolys, do not affect players, do not block VIS directly.
problems = hard to understand usage, and misuse may increase r_speeds; also ALL sides of a brush must be either HINT or SKIP, no other textures mixing allowed.
CLIP
used to block & guide player movement. It does not stop grenades or gunfire, is invisible, does not block VIS.
problems = misuse can be irritating, and ALL sides of a brush must be CLIP, no mixing textures allowed.
cli1.jpg
NULL
proposed in Valve ERC forums, possibly under development, to be used like CAULK in Quake, or SKIP in HL - except it can be mixed on a brush with other textures. It will remove that face it covers from the map. It will not block VIS.
problems = will probably be many....

Source For Information = http://www.countermap2.com | Source For Images = DroneZKe