Most of the Alpha textures are found in the Sprites texture folder. The easiest way to discover them is by looking at the surface properties. If the Alpha flag is on then some part of the texture should look transparent in the editor. A quick check whether a texture has got an Alpha Channel in KPRadiant is by selecting the texture. It should show pretty well if there is.

Alpha textures are used mostly to create fences and grids. These appear very often in Kingpin. But there are many other places where you can use them with a little imagination. The ones in the game are : vents, canal lids, train tracks and a few types of beams. These beams can replace a lot of brushes and hence helping you out when it comes to r_speeds.

Alpha Textures can be made in two ways. The first on is traditional and it is almost automatically dome when you put the Alpha Texture on - the Alpha surface flag. This way makes the visible part of the texture completly opaque. The second one is for using when you want 100% precise drawing. This one looks really good. It is done by making a func_wall entity and setting the surf_alpha flag. There are other entities that have this flag like doors. You must make sure that the alpha surface property is off when using surf_alpha.

Note: One big advantage of surf_alpha is that they are actually lighted and don't stay at full brightness like the normal ones do. Have in mind that your video card has to support multitexturing (gl_ext_multitexture 1). As far as I know all TNT or GEFORCE cards have multitexturing

Here are some ideas for using Alpha Textures:

You can make glass/transparent doors.
You can make rocket/grenade resistant clip textures.
You can make splashes and other marks on walls.
You can make lights look like projectors (like in Quake 3)

There are probably more so if you think of one then tell me about it and I'll put it here.

Unfortunately the Alpha Textures have some drawbacks which can be annoying:

Bullets go through them no matter what you try to do.
You can't make the faces dual sided (like in Quake 3)
With the surf_alpha flag you can see other brushes through them.
If you try to give them a window flag you can't see models through.

Well, that's about it. I may update this tutorial as I discover things. I may add pictures to better illustrate the creation and uses.

Suggestions and comments, etc. to :
oggie_k@yahoo.com