[Algorithms] Scorch marks on arbitrary geometry (was: Bullets on walls)

[Noel L. <ll...@ho...>]

So, after the interesting thread about putting bullets on
walls, I was wondering what people usually do to put
scorch marks (or any other decals) on arbitrary geometry.

It seems that most methods work well for regular or
"known" geometry: height fields, quads, etc.

The two ways I could think of so far are:
- Use projective textures. I haven't used this before. What kind
   of performance hit does it involve?

- Try to "face-map" the geometry we want to scorch to use
   texture coordinates from 0.0 to 1.0 in a regular way, and then
   draw it again with the scorched texture. This is particularly
   tricky if the geometry isn't face-mapped to start with, and especially
   if we want to do it without modifying the geometry at all (would need
   to find a texture transform that maps the original uvs into what we
   need).

How are people doing that today in games? Any recommendations
or ideas would be most welcome.
Cheers.


--Noel
ll...@ho...