Level of Detail

Lonesome Ducky · Post by **Lonesome Ducky** » Fri Jun 05, 2009 11:52 pm

Can anyone recommend to me a good site explaining how to go about simplifying meshes? I want to do it for LOD, obviously, and want to do it inside of irrlicht. I've looked on google, but haven't found anything overly useful.

Midnight · Post by **Midnight** » Sat Jun 06, 2009 1:30 pm

You would need some sort of algorithm for morphing the mesh.

this would be rather difficult to write from scratch but may be easier to do with the modeling tool and multiple mesh files, depending on the format perhaps even built in lod in the mesh.

I don't know of such an algorithm but I can't imagine a determined person couldn't find it.

perhaps bing would be better then google who knows get creative with your bad self.

I just used it myself and found this
http://www.gamasutra.com/features/20000 ... ner_01.htm
not entirely useful but it's a start.

hey check this out I think it works

http://www.scribd.com/doc/3124116/A-Sim ... -Algorithm

Masterhawk · Post by **Masterhawk** » Sat Jun 06, 2009 2:57 pm

you should check out this paper from stan melax

http://docs.happycoders.org/orgadoc/gra ... /gdmag.pdf

He shows you how to implement a working progressive mesh algorithm.
the source is also available. the link should be found in the paper.

Lonesome Ducky · Post by **Lonesome Ducky** » Sat Jun 06, 2009 3:04 pm

That's great! Thanks to both of you

Mel · Post by **Mel** » Sat Jun 06, 2009 4:02 pm

Or else, you could do the LODs manually and create an ISceneNode which swapped between them given the height in the screen, the distance to the camera, or whatever another algorithm you saw fit to swap between them

Requires less effort and is a valid approach.

FuzzYspo0N · Post by **FuzzYspo0N** » Sat Jun 06, 2009 4:24 pm

Most times the LOD is stored in the same mesh, and premade using tools that are built into the 3d apps. (3dsmax etc)

Lonesome Ducky · Post by **Lonesome Ducky** » Sat Jun 06, 2009 4:43 pm

I know, I just thought it would be fun to do. I plan on making a scene node that generates a few levels of detail right when you load it, you can specify how many levels there are, the detail, and the distance.

Masterhawk · Post by **Masterhawk** » Sat Jun 06, 2009 6:06 pm

Lonesome Ducky wrote:I know, I just thought it would be fun to do. I plan on making a scene node that generates a few levels of detail right when you load it, you can specify how many levels there are, the detail, and the distance.

Well that's exactly the thing I wanted to do after I finished my bachelor-thesis on this topic. But that you will do it suits me

LOD-SceneNode would be a nice feature to have within irrlicht.

Lonesome Ducky · Post by **Lonesome Ducky** » Sat Jun 06, 2009 7:36 pm

Well if your up to, I'd rather you than me. I'm not exactly well versed in mesh simplification, but I'll give it a try. A few things I'm wondering are: Does irrlicht store each frame of a vertex animated model in a separate mesh? And: How would I best remap the UV's after simplification?

Steel Style · Post by **Steel Style** » Sat Jun 06, 2009 10:10 pm

UV remap depend of your method to simplify models, and it's the real challenge in my opinion, you'll need to support things like tilling and much more. Maybe try to do X level of detail generated at the start and for each one try to create in real time a new texture for them, that you will store.
But the problem now is about memory ...

Lonesome Ducky · Post by **Lonesome Ducky** » Sat Jun 06, 2009 11:34 pm

Well I was thinking with edge collapse, that for the new vertex I could just take the average u and v of the 2 vertices I combined. Would this be a good approach?

devsh · Post by **devsh** » Sun Jun 07, 2009 9:17 am

binary triangle fusion???

drawing every 2nd,4th,8th indice??

loki1985 · Post by **loki1985** » Sun Jun 07, 2009 9:25 am

i don't think there really is such an easy solution which will work on average meshes.

i once heard the marching cubes algorithm being used for mesh simplification too.

or try this: http://cg.cs.uni-bonn.de/aigaion2root/a ... 6-mesh.pdf

it doesn't look easy, but the screenshots look really promising.

Lonesome Ducky · Post by **Lonesome Ducky** » Sun Jun 07, 2009 2:19 pm

I think I'll go with edge collapse first, to learn a little more about simplification. But that method does look very good, I might try that after.

Midnight · Post by **Midnight** » Sun Jun 07, 2009 5:14 pm

Masterhawk wrote:you should check out this paper from stan melax

http://docs.happycoders.org/orgadoc/gra ... /gdmag.pdf

He shows you how to implement a working progressive mesh algorithm.
the source is also available. the link should be found in the paper.

that's the same thing I posted.

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