by stuart » Mon Sep 08, 2014 1:32 pm
Hi lomar,
The different materials.xml files reflect different texture sets. We have at present, two global textures sets (one with .png images, one with .dds) and a "regions" one, which defines different textures and effects depending on where you are in the world.
The current development stream includes a new materials.xml format which makes a lot of this easier. I'd strongly recommend developing any new feature against that rather than the V3.2.0 (or indeed the V3.0.0) release.
As Hooray points out above, it should be straightforward to create grass based on the tree shader, and you could probably prototype just by modifying the materials.xml parameters to create many more smaller trees (see Docs/README.materials for what the parameters are).
However, the trees have a memory footprint. This is fairly small, but obviously there are many more blades of grass than trees! While I haven't done the sums, I'm fairly confident you couldn't use the same approach for grass. Instead you'd probably want to do something much more clever. For example, you might define an area (say 50mx50m) of defined volumetric grass, and then apply this just to the scenery underneath the aircraft, clipping to the scenery triangle edges, and using a translation on some wind/height function so that as you moved around, the apparent grass moved passed you.
Have fun!
-Stuart
G-MWLX