Overlay layer rendering

[Thorsten]

Since integrating the grass shader, I've been thinking that a geometry shader extruding a couple of shells ought to be good for a lot of things - finally I've found the time to tinker with this.

Small-sized volumetric vegetation layer extruded between the trees - seeing this for the first time, I immediately realized what we've been missing forever - it looks much more real than just trees and bare terrain underneath.



But it can do much more - extruding some micro-structured rocky surface from the ground:



Might be a while till this is good to go, I still need to take care of pesky issues like lighting and fogging, but expect it for for the 2017.4 release.

Credit for coming up with the underlying technique goes to IcecodeGL of course!

[wlbragg]

Thanks to both of you! Looks incredible.

[Icecode GL]

That looks really, really good! The forest looks a lot more populated now.

[Necolatis]

Looks fantastic. Do you know if it will be lighter on the GPU than grass?

[Thorsten]

Do you know if it will be lighter on the GPU than grass?

That is a joke, right?

I hope it is...



(It would depend on what your bottleneck is - there is a geometry shader involved, but I'm trying to cut down the number of layers that are extruded to about a quarter of what grass needs - so the fragment shader load gets lights - but at the same time this is rendered quite a bit farther out, which means we can't cheat so easily on fogging and lighting,... I think the bottom line is, I have no idea, but it's not going to be cheap).

[Thorsten]

I've done some life case performance testing of this today. The good news is - I can't really measure the impact against all the other settings maxed out. The bad news - that's on a GeForce 1080.

So it'll do find on a high-end graphics card - on others it'll probably be like the grass (I've figured out the hard way that I need to attach a surface normal in the geometry shader for this one... so per triangle and per fragment this is more expensive than grass, but... less layers).

[Icecode GL]

I was thinking that maybe a better alternative for your purpose is parallax mapping (basically what the urban shader is using). It's cheaper on the GPU but looks worse closer up. Sides look better though, since it doesn't rely on layers like shell texturing. It also requires some more work on the artistic side and it might be hard to integrate with noise functions since it's a purely texture based approach. Just thinking out loud.

[Thorsten]

We do parallax mapping to simulate terrain roughness, the urban shader is using height mapping - I've tried that for terrain as well and discarded the approach again, the pain/gain ratio wasn't good.

Basically parallax mapping can't draw really elevated stuff, height mapping tiles like mad if you use a height texture and is too slow if you do it procedurally - if you mix you get into all sorts of pain due to the normal being a vector but height being a scalar, so there's no easy way to derive modified normals,...

Should I go on?

[Icecode GL]

height mapping tiles like mad if you use a height texture and is too slow if you do it procedurally

Yeah, that's what I thought. I guess there is not much else we can do about performance then. Since the bottleneck is in the geometry shader (I think), you can also try doing a more aggressive LOD if you haven't already.

I really don't get why people get a bad performance with this shader. On my 4-5 year old machine I get solid 60fps with the grass overlay enabled and ALS at max. The effect is kind of demanding, but it's reasonable enough, i.e. you can't expect to run FG on full specs with a 7-8 year old PC.

[Thorsten]

It's for the higher end of the GPUs, I've accepted that, I won't needlessly waste framerate but I also won't cut on appearances and if not everyone can run it, well, it's optional. Time works for us here...

[Thorsten]

Hm, I just realized we can have two overlay layers for almost the price of one (and an additional texture lookup), since one can use both (noise) and (1-noise) to generate two mutually exclusive bump patterns on the same geometry.

Pretty neat... So we can have both boulders and shrubs for instance if the density isn't too high.

[Thorsten]

... and the layer info can be used very nicely to let the whole thing vanish in snow... so this is gonna be good...

[Icecode GL]

Looking forward to the results! Sounds really nice.

[Thorsten]

In time for the release, I've now documented the configuration of this effect (which is currently available for Hawaii, Scandinavia and parts of the Mediterranean) in the wiki - so if anyone wants to use it for his own regional definitions, this is now possible.