Created 20 years ago2004-06-19 23:18:22 UTC by Raizner
For a good explanation on VIS, vis-blocking and hint-brushes:Book mark and download this tutorial... It is Geoff DeWans original and the best explanation of Vis and Hints that I have come across. Some of the info is a bit dated, but the theory is sound.
http://www.gamedesign.net/book/view/266
The article is about Quake but the whole thing is about the same for HL. This may be a helpfull article I was just recently attended to.