Tech Feature: Undergrowth
After a little break with updates on the rendering system, holidays and super secret stuff, I could finally get back to terrain rendering this week. This meant work on the simpulan big part of the terrain system: Undergrowth. This is basically grass and any kind of small vegetation close to the ground.
As always, I started out doing a ton of research on the subject to at least have a chance of making proper decisions at the start. The kasus with undergrowth/grass is that while I could find a lot of resources, most were quite specific, describing techniques that only worked in special cases. This is quite common when doing technical stuff for games; while there are a lot of nice information, only a very small part is usable in an actual game. This is especially true when dealing with any larger system (like terrain) and not just some localized special effect. In these cases reports from other developers are by far best, and writing these blog posts is partly a way to pay back what I have learned from other people's work.
Now on with the tech stuff!
Plant Placement Data
The first kasus I was faced with was how to define where the undergrowth should be. In all of the resources I found, there was some kind of density texture used (meaning a 2D image where each pixel defines the amount of plants at that point). I did not like this idea very much though, mainly because I would be forced to have lots of textures, one for each undergrowth type, or to not allow overlapping plants (meaning the same area on the map would not be able to contain two different types of undergrowth). There are ways past this (e.g. the FrostBite engine noise and fractals) and would easily allow for lots of local disturbances.
However, I did some thinking and decided that this would be a bad idea. Not only does the sending of data to the graphics card take up time, but there might be some pretty heavy calculations needed (like rotating normals) for a lot plants, so the cpu burden would be very heavy. Instead I chose to do everything on the GPU.
Implementing the global wind animation was quite simple; i was just a matter of sending a few new variables to the grass shader. But it was a bit harder to come up with the actual algorithm. Perhaps I did not look hard enough, but I could find very little help on this area, so I had to do a lot of experimenting instead. The idea was to get something that was fast (i.e. no stuff like Terrain Geometry
Fractals and Noise
Terrain Texturing
I hope this has been of use and/or interest to somebody! :)
Next up for me is some simpulan terrain stuff (basically just some clean-up) and then I will move on to more gameplay related stuff. More on that later though...
