Some AHL mappers asked for a tutorial on doing this, so I gave them a basic description of what to do. I'm not quite where I need to be to write an offical tutorial at this point, but this is enough to get anyone interested going:
http://collective.valve-erc.com/index.php?doc=1076548934-94242500
That tells you how to get them in-game, but not much about what they need to actually look like. I had to use a lot of trial-and-error to get stuff working.
The trick is that RGB 128 128 128 is the shade of gray that has 0 effect. A good detail texture has variation from around 115-140 from what I'm finding. You can adjust brightness/contrast in Photoshop to match what you need. If you are taking a regular texture and desaturating it to use, you usually have to reduce contrast a LOT. Note that having the average brightness above or below 128 will brighten or darken the texture in-game. So the best way seems to vary a little above AND a little below 128. You can run across the texture with the eyedropper tool while adjusting the brightness contrast, to get a feel for where the texture's variance lies.
Here's an example of part of my text file for temple, ahl_temple_detail.txt. You can add notes behind // that don't effect the file, which helps keep the stuff straight:
//floors x1
pk_floor1a detail/jx_detail01 6.0 6.0
pk_floor1c detail/jx_detail01 6.0 6.0
The numbers are the scaling. Depending on the size of the detail texture (go for square; 64, 128, or 256) and the scaling of the other texture in-game, the need varies. I find values between 6 and 14 are working best. I'd start with around 8 then see if you want it smaller or bigger.
Here's a zip for the texture I'm using on the floor in Temple, as well as a 64x64 grey texture if you want to make your own in photoshop using the texturizer or something:
http://www.cryotank.net/remote/detail_ex.zip
I have keys bound to turn the detail textures on and off, to compare. It helps you see what effect it's really having. Remember, these are OFF BY DEFAULT (in AHL, at least). So you have to turn them on yourself. So in the console set:
r_detailtextures 1
I'll write up an 'official' tutorial with more info and sample textures when I get my current map done, as well as some more tinkering/learning.
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