I have a bit of a challenge. I want to generate a navmesh for HL maps as I'm creating a bot for some HL1 mods (especially Natural Selection) which have limited or no bot support.
To do this, I'm currently extracting all of the vertices from the BSP file and rendering them into a triangle mesh. Vertices exist for all visible entities in the BSP file, but I am excluding func_illusionary entities since these do not collide and therefore should be excluded from navmesh generation.
The challenge I have is clip brushes. These are used for things like chain-link fences and railings where the visual brush is a func_illusionary and then a brush with the CLIP texture is added to prevent players walking through them. The problem is that brushes with the CLIP texture are special cases and do NOT appear in the list of vertices (presumably because they're never rendered): they exist only as collision hulls.
The result is that right now, I only have two choices: include func_illusionary entities in navmesh generation, and have the AI unable to walk through things like the cs_747 curtains and other decorative features, or exclude them and have the AI try to walk through the chain-link fence in cs_militia.
The preferred option of course is to have the clip brushes retrieved and added to the list of vertices, but currently I have no idea how to do this. I've had a look at the hlbsp project's breakdown of the v30 map format here and the map optimisation tutorial here, but I'm still unsure how to convert the planes into a set of triangles. As far as I can see, they're defined as a set of infinitely wide and tall planes with a normal and distance from origin.
Has anyone managed to do this before?