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Tips on making rounded or cylinder-based objects with low LI


Bitsy Buccaneer
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I've been reading as much as I can, experimenting in Blender and the Beta Grid, lowering physics, adding simple shapes for low and lowest LOD, and my attempts are still coming in at higher LI than objects I've examined inworld. Mine have fewer tris too, so I'm at a loss.

What I'm trying to make are some small, rounded bottles and jars. I've started with the simplest shape - a lid (no inside faces), straight sides and some beveling around the edges. Something like this:

Ye Olde Roman Cold Cream Jar.png

I'd love to make more complex shapes like others are doing too. 

Any tips much appreciated. TIA.

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The first thing you need to do is to look at the download and physics weights separately. You don't tell us how you specified the physics, or it it was default, but the physics weight can be responsible for high LI. The uploader tells you the default "convex hull" physics weight. If you are using "prim" type physics, you need to look inworld using the "More Info" link on the edit browser to see these weights.

Next, what about size? The download weight part of LI is very dependent on size. Are you looking at the LI at the final intended size?

Then, for small items the download weight is dominated by the lowest LOD version of your object. How are you making the lower LOD meshes? The default automatic LODs may be inappropriate.

Lastly, the thing that correlates most closely with the download weight is not the number of triangles (12 bytes of data each), but the count of vertexes you see in the uploader (16 bytes each). This is not generally the same as the vertex count in your modelling software because vertices get duplicated if the same goemetric point appears in adjacent triangles with different normals and/or different UV coordinates. So flat shading (sharp edges) and fragmented UV maps can lead to very large increases in vertex count, download weight and LI.

 

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My apologies. So far on the beta grid, I've just set the physics to lowest and it pretty much always comes out to .2. I did make a .01 m cube to try as the physics upload. I don't need 'physics' for it. It's just an antique to sit on a table. So if I'm understanding things correctly, the physics is low enough it won't be affecting the LI. Other aspects of performance perhaps, but not the LI.

I've been uploading the jar lid at .1 m x .1 m by something smaller. 8 vertices to start with in the cylinder gives a good LI (.5), but a less than round shape. A cylinder based on 16 vertices is better (but still not great) and gives .8 or so I think. Since this is only half of the piece, I'd really like to get that down. I'm also trying to learn best practices on easier pieces. (Working with two bits in a mesh object is causing all sorts of problems that I haven't gotten the hang of accomodating yet. The one I posted shows a bit over 400 triangles, don't remember vertices (everything I've read has been focused on tris); it won't upload on the beta grid cause of something I don't understand yet that's probably related to it being two separate pieces in Blender.

I haven't gotten to the seams or UV map yet because I've just been focused on the shape. I did take a peek at it on one trial and it was a twisted mess. Could that be causing the problems? I'll improve that tomorrow.

Eyeballs crossed,

B

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If you upload a mesh without a UV map, the result is unpredictable, because the uploader appears to use uninitialised data instead. Sometimes its all zeros, so the surface is all textured with one pixel; sometimes it's random, which gives the sort of effect I think you are describing. The latter also usually means the map is completely fragmented, which gives the highest possible download weight - each vertex gets repeated for every triangle (usually 6) that shares it. So the LI you are getting may be much higher than you would get in a UV mapped version.

The minimum LI for any mesh object is 0.5 (sever weight). So if you have separate objects for cap and jar, you will always end up with at least 1 LI. Instead, you can make them two materials on the same mesh. Then you can aim at 0.5 for the combination.

You seem to have four segments of bevel on your jar top. It should be possible with less. Try experimenting with bevels with two segments and varying the Profile (I am assuming Blender here!). A profile of 1.0 will keep the beveled edges in the plane of the adjacent faces (as if you used loop cut & slide instead). This has the effect of leaving the adjacent triangles shaded as they were before bevelling, but with rounded shading along the edge. Profile 0.5 is the default, which leaks the rounding effect into the adjacent faces. In all cases, you need to be using smooth shading. Use Matcap shading to see the effects in Blender.

Instead of bevelling, you can use an all-smooth smooth shaded object and a normal map to "repair" the horrible shading that gives you. In the picture, both the left two jars have download weights of less than 0.3 (size 0.1 x 0.1 x 0.1), because they share the same horribly decimated lowest LOD (LODs top=high to bottom=lowest). The left mesh uses bevels to get the right shading. That's a lot of extra geometry which means it has to use medium and low LOD meshes to get that low weight. The middle jar is the same geometry as that on the right, no bevels and smooth shading. On the right it has no normal map. In the middle it has a normal map baked from the high LOD mesh on the left. Tha noamal map is only 128x128, so the texture load is small. As it is much less geometry, this jar can use the same mesh for the three higher LODs. It isn't quite as nice for the highest LOD as the jar on the left, but it's better at the intermediate LODs. However, the normal map will only work for viewers using advanced lighting. Without the normal map, it will look like the jar on the right. So the choice may depend on who is going to look at it.

jars.jpg

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Thank you so much Drongle. All of that is taken on board, even if it did take me two days and about seven reads. :-) I'm trying an 8 point cylinder as medium and low, and maybe a cube as lowest. A .01 m cube for physics (.360). I get a 1.219 LI & download cost for the complete piece (one object including a handle on the lid), which might be good enough for now. Am going to attempt texturing it to see if that distracts from the shape change.

A 1 profile on the beveling gives what looks like a right angle. My current version has a deeper round to the bevels and I can't come close to approximating it with 2 segments. Will keep experimenting with all of this.

Am off before I confuse myself. Writing about mesh and blender is even harder than using it. :-)

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Just when I thought I was maybe getting the hang of things..... :-)

I have no idea what I've done, but it's now LI of 1.099 with a handle on top. Am considering being happy with that for the moment. Took me twelve hours to get up the courage to test my texture attempt inworld and it actually looks mostly alright. Hurrah.

The thread you posted is a bit too advanced for me. Hopefully I'll be able to use the info some day soon. Thanks again.

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Am below 1 LI/download if I use the same basic 8 point 'cylinder' for Medium, Low and Lowest. I think it even looks alright enough - except that the fancy high one has a wee handle and the basic not quite cylinder doesn't (cause it seemed a detail that could be sacrificed without much loss). No matter how squat I make the basic Med-Low-Lowest version, it expands to the full height of the Highest, which is the pot + handle.

Is there any way around this besides adding a cube for the handle on the Med-Low-Lowest version? I doubt many people will notice if the wee handle goes poof but the pot suddenly increasing in height is a bit shocking.

pyxis comparison for forum.png

 

 

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Bitsy for something small and simple like this, I would just use the Decimate modifier to make lower LODs. (Actually that is a lie, I would use the auto generator in SL, while watching the preview as I bumped the numbers up a bit.) 

 

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All the other meshes, lower LODs and physics, are stretched or squashed by the uploader to fit the bounding box of the high LOD mesh. So if you take the knob away, you need to to have something level with the top of the knob to stop it being stretched. There are tricks to get around this, but I think you might want to get a bit further with the basics before getting into more complicated stuff.

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