Re: [Flightgear-devel] Volumetric grass

[Renk T. <tho...@jy...>]

> This could actually be used also for runways and the apron, just with  
> very much shorter grass and lower density? Could it be possible to match these
> patches of grass with the underlying ground texture like we do with  
> trees?

You mean the placement masks? Technically that's entirely possible because grass patches are just another species of random trees as far as the shader is concerned, so the same options apply. 

In practice, if you use an airport keep or runway texture that's not very homogeneous, you will get *really* bad tiling since the texture is repeated at high frequency (in fact, I had to postprocess my gravel shots to make non-tiling textures despite the fact that they were looking pretty uniform in the first place), so the only way to draw patches of different stuff is procedural overlay, but since we do that on the GPU per frame and the placement mask on the CPU at LOD level load time, we can't currently generate a matching placement mask.

(I'm not sure this works even in principle, because the limited accuracy of the GPU numerics in addition to architecture-dependent specific might mean that you can't generate a pseudo-random number generator that works the same way on both CPU and GPU for every architecture... - always wanted to try it though...)


> Gravel runways could have some green growth, perhaps increasing towards  
> the outer edges of the runway?

They sort of do have green right now...

http://wiki.flightgear.org/images/6/61/Dirt_rwy.jpg

making it dependent on the distance to the runway edge is not a bad idea, it depends on how precisely the uv-mapping is done, but I have a feeling it should be feasible. But it can't easily be volumetric (see above).

Well, perhaps we might want to revisit dirt runways - I am quite happy with the gravel options for the airport keep these days.

http://users.jyu.fi/~trenk/pics/airport_keep05.jpg

> Smaller asphalt runways could even have some cracks with grass growing through. 

Procedural cracks are a bitch to get right - I spent a week on the rock crack algorithm, and I'm still not happy with it from close range. And non-procedural cracks will tile - see above. Perhaps a semi-transparent overlay with the strength determined procedurally might work.


> Soft runways' grooves will be filled with water during rain, asphalt is  
> more uniform since the surface does not wear as much.

Since Christmas is near - anything else we can render for you? What about oil films in the puddles perhaps? Tire tracks in the mud? :-)

* Thorsten