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 Post subject: Volume size
PostPosted: Wed Feb 23, 2011 7:39 am 

Joined: Fri Feb 18, 2011 8:41 pm
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Hey David, I was wondering.

How big can we make our terrain (using the smooth version, not the minecraft version) ? Considering there is no streaming yet, what's possible for now?

Also, how much disk space does it take? and RAM? Thank you :)

(P.S., do take into account frustum culling and maybe even occlusion culling)


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 Post subject: Re: Volume size
PostPosted: Wed Feb 23, 2011 8:20 pm 
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You're going to need to do some experimentation here, because it will depend a lot upon your data.

Uncompressed volume data will typicaly take 1 byte per voxel, so a 1024x1024x128 terrain would take 128mb. If you fill this with 3D Perlin noise you'll probably get a compression factor of about five or so (this is using the new Volume class which is currently in the branch). If you have just 2D Perlin noise representing a heightfield you'll probably do better. In the comments of Volume.h in the new branch there are some untested ideas about how compression can be maximised.

The other issue is the extracted mesh. This will possibly take more space than the volume but again it really depends on the data. But you may only need it on the GPU, unless you also want it on the CPU for physics. Or the CPU version could be lower resolution/decimated.

As for frustum culling/occlusion PolyVox has no concept of these. It operates at a much lower level of simply extracting meshes from volume data. You need to implement these features at a higher level in your game engine.


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 Post subject: Re: Volume size
PostPosted: Thu Feb 24, 2011 5:46 am 

Joined: Fri Feb 18, 2011 8:41 pm
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Oh yes, what I meant about frustum culling is how much data and how far away do you think we could show, with the engine in question having frustum culling and occlusion query.


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 Post subject: Re: Volume size
PostPosted: Thu Feb 24, 2011 8:13 pm 
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Unfortunatly I can't say... there's just too many variables and I haven't tested much myself. There is a demo while features a 1024x1024x256 map (the map is called hills_large) which you can try here:

http://www.thermite3d.org/releases/Thermite-July2009.zip

It's a pretty old demo though - lots of room for improvement. Also I've been using frustum culling but not occlusion queries, so it just draws everything in the frustum.


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 Post subject: Re: Volume size
PostPosted: Thu Feb 24, 2011 8:25 pm 

Joined: Sat Sep 18, 2010 9:45 pm
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If you use Ogre3d there is even a coherent hierachy occlusion manager which I gotten to build on ogre 1.8. The demo works fine but I wasn't able to get it working in my own app and I just left it there due to time. I will eventually get back to it.

Oh yeah, and there was bugs in it which cause it to perform worst than regular scene manager, but someone on the forum said once they fixed the bug it was better performing.


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 Post subject: Re: Volume size
PostPosted: Fri Feb 25, 2011 5:24 am 

Joined: Fri Feb 18, 2011 8:41 pm
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coherent hierachy occlusion manager? how does it work?


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 Post subject: Re: Volume size
PostPosted: Fri Feb 25, 2011 5:29 am 

Joined: Fri Feb 18, 2011 8:41 pm
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David Williams wrote:
Unfortunatly I can't say... there's just too many variables and I haven't tested much myself. There is a demo while features a 1024x1024x256 map (the map is called hills_large) which you can try here:

http://www.thermite3d.org/releases/Thermite-July2009.zip

It's a pretty old demo though - lots of room for improvement. Also I've been using frustum culling but not occlusion queries, so it just draws everything in the frustum.


The demo is crashing for me when it starts extracting the surface. (even though I can already see the tank on some ground)


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 Post subject: Re: Volume size
PostPosted: Fri Feb 25, 2011 6:23 pm 

Joined: Sat Sep 18, 2010 9:45 pm
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Oh sorry I meant coherent hierarchy culling: the CHC and CHC+ algorithms.

http://www.google.com/search?hl=en&rlz= ... 1&aql=&oq=

Someone on the ogre forum implemented CHC (not the CHC+) manager in Ogre. I don't know how the details of the algorithm you have to read the paper to find out (I think there is a GPU gems article on it also). Well AFIAK, it does intelligent management of hardware occlusion to get around some of the problems associated with it.


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 Post subject: Re: Volume size
PostPosted: Fri Feb 25, 2011 7:04 pm 

Joined: Fri Feb 18, 2011 8:41 pm
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Thank you, I will look into implementing this in MLE. :)


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 Post subject: Re: Volume size
PostPosted: Fri Feb 25, 2011 7:30 pm 
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Shanee wrote:
The demo is crashing for me when it starts extracting the surface. (even though I can already see the tank on some ground)

Ah, unfortunatly I can't help with that as the demo is pretty old. My machine is two years old and gets 35 FPS if I position the camera so that the whole 1024x1024x256 volume is in view. So there is no culling and also no LOD is present.


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