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Madeliefste Oh

Mesh and sculpt - comparison of LOD

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Often I hear the argument that mesh has a much better LOD then sculpties. Now I had made a lamp that has no optimal LOD. Since the model was very easy to make in mesh, I did that and uploaded both sculpty and mesh to the beta grid.

For uploading the mesh I used the automated LOD setting from LL (Prim count 1,55). This is the result.

The mesh is on the left side, the sculpty on the right.

MeshSculptLOD.jpg

Pic 1: At level 3 and 4 both stay in shape
Pic 2: At level 2 both start to loosing shape
Pic 3: At level 1 sculpt stays the same as at level 2, while mesh even looses more shape

So actually I don't see it, this much better LOD of a mesh. In my eyes the lod of the sculpt is better, at least in this test. I looses its shape in a less drastic way, and it does not loose again at level 1.

Any other people who did comparision tests? What were your results?

 

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Haven't done much testing yet, but krikey, that doesn't look good!

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HI Madellefste,

I assume that the designer of the sculpty took into account the knew LOD behaviour of a sculpty and placed the vertices accordingly to reduce the LOD effect.  The mesh you made was decomposed by the uploader software which cannot make such decisions as it has no idea about which areas are of importance and which are not.  You could make your own LOD for the mesh and this would work quite well, possibly using even fewer vertices than the sculpty with automatic LOD. As discussed at length elsewhere the cost of the mesh will be 2 PE over the 1 for the sculpt, so this is not as good for simple objects.

In short unless you make your own LOD for mesh you are at the mercy of a piece of software that has no idea how to keep important features.

Cheers ^_^

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I'm the creator of both the sculpt and the mesh. And yes.. when I create sculpts I take lod effect in account when designing the sculpty. When I would do the same with mesh I get a much heavier model. And thus a much heavier prim count. Since I have the model in mesh now already I can do a test to see what a good level of detail will cost for mesh compared to a 1 prims sculpt.

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Yep, like Chodai stated, with a sculpt you have to build from what is there. With mesh you are totally free how your LODs will look. The automatic LODs from the uploader may work for organic shapes quite well.

The pictures below are not a direct comparison with a similar sculpt, though I think it shows what handmade LODs can do.

It's textured with a 512x512 and a 256x128 texture.

aR-Rifle-LODs-01.jpg

 

 

 

As you can see on the next picture, the gun stock is made of a single mesh, with even less triangles than a single sculpt.

aR-Rifle-01.jpg

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Test 2

Maybe I am doing something wrong. But what I did is this: I made the model much heavier, and uploaded again, while I let the automated LOD settings calculate the levels.

The most left is the new heavy model, as you can see it's possible to reach a very reasonable lod.

MeshSculptLOD2.jpg

The mesh stays perfect in shape, till we reach level 1. There the model starts to loose shape as well.

So it will be possible to create a perfect lod for your meshes, but it will cost some. The newest mesh I just uploaded has a prim cost of 22.

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Try thinking the other way around. What is at least needed for the lowest LOD to keep the shape and look of your mesh from a distance. For your lamp that would be 9 triangles (4 planes) with an alpha texture. Why 9 Tris and not only 8? Because you have to keep the texture from the other LODs as well.

From this you can build up to your Hi LOD.

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Whatv arton said. The auto LODs are very poor unless your mesh is rather smooth or has lots of small detail. Rather than wasting vertices by adding them at the high LOD just to improve the low LODs (although this will not cost too much for smaller objects), just make custom LOD meshes that retain the detail you need. You can even use the same mesh at successive LODs if you need to.

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I think, this is a good starting place:

    http://blog.machinimatrix.org/kettle-quest

That is an article about comparison between Sculpties and Meshes and i hope it explains a bit, what is going on. Meanwhile i have released part I of the article as Video tutorial (can be found on the page above). I am in the middle of Part II of the tutorial series where i explain how to make better LODS. I believe that the video will add a few tricks anf hints to what you already can find in the article.

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I'd keep some things as sculpts. Things with a dozen or so edges that dont stretch too much, like the above example. And rocks.. organic shapes.

But also as we know, mesh needs to be optimised. .. say it with me... the mesh needs to be optimised. Sadly, many won't be and there will be a whole lot of suffering going on and the meshes = lag or mesh is crappy are sure to be a hot forum topics.

 

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I found another issue with Mesh LOD. While making my video i tried to compare a Sculpty and a mesh with exactly the same internal mesh (i exported a sculpty as mesh). I also made the LOD's of the mesh according to how it is calculated for Sculpted prims. My expectation was that now both objects behave exactly identical. But they don't do that, meshes go to the next lower LOD much quicker.

I have created a Jira for this ( https://jira.secondlife.com/browse/CTS-673 ) , because it looks wrong to me. if on the other hand mesh is supposed to change its LOD shape earlier than Sculpted prims, then we now have got another parameter where mesh is worse than sculpties. Here is an image comparison:

Sculpty on the left, mesh on the right (For the handle i made a mistake on the LOD, hence the upper right and the lower left handle look a bit different. If i had done it correct, then they would look exactly the same). Nevertheless you can see on both images, that the Mesh objects turn to lower LOD much earlier than their Sculpty equivalents

The upper image was made from about 40 meters away. there you see that both pots look very similar.
The lower image was made from about 60 meters from the kettles. there you see that the mesh has already transited to LOD0. The Sculpty does that when i am about 70 meters away from the kettles.:

kettle.png

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Gaia. Do they have the same size bounding boxes? The switches are supposed to be when the camera distance is 1/0.24, then 1/0.06 and then 1/0.03 times radius (half diagonal of bounding box).  At least that is for meshes. I can't remember for certain if it's the same for sculpties, but I would expect so.

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