Quote:Original post by Mike2343
Honestly why do you need it? The GPU can more then handle the verticies.

This argument ("You don't need LOD nowadays") aways comes up. And it's always wrong.

Say your poly budget was 1000 tris for the landscape. Now I could just brute force it and render the nearest 1000 in the view and it'd look ok. But if I actually had LOD then I could use those 1000 more efficiently and get the same visual quality but twice the draw distance. Thats going to be true no matter how high your poly budget actually is.

The real question is how complicated your LOD system needs to be. IMHO you don't need anything more complicated than geomipmapping. Nice high detail terrain, and switch to different sets of indices for farther away. Don't bother with geomorphing or anything complicated, just make sure that the transitions are far enough away so the snapping is minor.

Likewise for crack fixing schemes - keep it simple with something static like skirts. You still get LOD, but you're doing a minimal amount of CPU work and just letting the GPU do what it does best - blast through big chunks of static geometry.

Quote:Original post by OrangyTang
This argument ("You don't need LOD nowadays") aways comes up. And it's always wrong.

QFT.

Particularly with some of the lightweight simplistic algorithms -- geomipmapping would be my choice -- you can perform LoD very efficiently. My own terrain system performs LoD with negligible performance penalty (it's a couple tens of thousands of cycles per second), and the poly counts are cut back sharply as a result. (Exact values depend on configuration, but it's generally 10%-20% of what the brute force would render, with no visible artifacts.)

And yes, I know Carmack said it. And I say he's wrong.

Funny, from what I read Carmack isn't using terrain LOD in his new engine. I personally know he's better then me so I assume he has a valid reason and has done the research.

I've seen what Ysaneya (very impressive btw) but having skimmed his Journal from time to time I've not actually seen him mention LOD. I'm not saying he hasn't but I've not seen it. Also, most of us aren't doing what he is doing. Most are working on limited range terrains (a 6' person can only see so far before something obstructs the view and 8x8-16x16 miles is normally more then enough for most FPS games).

I'm also talking MODERN hardware, not GF3 or older here (likely excluding GF4 too at this point).

1000 tri's for terrain? That's the face count of some LOD models ;-) But in all honesty if that's your triangle budget for terrain you're likely working with older hardware and I already said that I wasn't considering it.

Remember the OP has not stated exactly what this is going to be used for, or how far he needs to see. I was just pointing out for limited range terrain engines (under 16x16 miles or so) you can brute force it in most cases (higher density meshs of course will require it).

Edit:
You posted as I was typing mine up lol.

Quote:
And yes, I know Carmack said it. And I say he's wrong.

If you're a better programmer then him, more power to you. Like I said, in OUR case the poly count wasn't an issue compared to the CPU cycles we wanted to give up. It's also a mute point since the terrain engine is now shelved for the time being. Also, I'm not a Carmack fan (he's an awesome programmer, I just down't worship any coders period, it's a rule of mine) but I was brute forcing awhile ago and came to my own conclusion (you can believe it's wrong or right, I honestly don't care worked for us) that brute force was better for us and that the GPU could easily handle it.

Anyways, out until tomorrow I think. Take it easy.

Quote:Original post by Mike2343
1000 tri's for terrain? That's the face count of some LOD models ;-) But in all honesty if that's your triangle budget for terrain you're likely working with older hardware and I already said that I wasn't considering it.

I deliberately picked a stupidly low number to show a point - that no matter how big (or small) your poly budget actually is, you can always get better results by spending the polys where they matter (ie. using LOD).

This thread is derailing quite a bit, shouldn't we return to giving the op resources he wants? Surely it's up to him to decide whether games should have LOD, it's his thesis, not yours ;)

First of all I have got a lot of inspiration out of the discussion, and some of problems has been revealed to me. I will work with this further. And this discussion was exactly what i wanted so I am happy :-)

Quote:
Seriously though, I think you should build your terrain engine as normal, profile, with and without LOD, see what speed/view distance tradeof works best in your case.

Yeah this would be an idea and I will probably consider each of the methods. The hard part would be to specify what method would work under which circumstances and how to specify the criteria to describe the circumstance;-) But I guess that
also has a lot to do with the experience, which I will be getting a lot of in the next year.

I got to wonder though about how to make caves/overhangs in the terrain. I know I just read about it a week ago and I cant seem to find the information about it now. It was something about using a second heightmap. Does somebody have an idea on how to do this?

Also i found a report on this site that utilizes a mixture of a couple of the most popular algorithms. What is your take on that?

regards
thallish