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Old 10-16-2013, 07:36 PM   #1 (permalink)
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Hints / Tips for Low LI Mesh

There is a lot of mesh on the grid that has insanely low LI for what appears to be the complexity of the item. There are many examples but two would be Kriss Lehmann's Tuscan Wood Cart coming in at 3LI and Pilot's Nail Polish Rack that is a jaw-dropping 1 LI. On the other hand, I also see what appear to be simple meshes that have an unexpectedly high LI.

I only play around in Blender as an amateur and certainly nothing I'm willing to share or upload yet, but when I asked friends about this, I generally get something along the lines of "oh, it's very complex and depends on X, Y, Z."

While I wholly accept this may be due to a variety of factors, are there any simple/basic tips that creators use to keep LI down (especially in Blender)?
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Old 10-16-2013, 07:38 PM   #2 (permalink)
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Make your own meshes

Build to scale

Remove unseen faces

Know how to texture to mask low poly

Customize your LOD
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Old 10-16-2013, 07:57 PM   #3 (permalink)
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Remember that physics shape can cause high LI too.
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Old 10-17-2013, 03:14 PM   #4 (permalink)
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I recently found this that might help a bit:

The Secrets of Mesh Landimpact
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Old 10-17-2013, 03:32 PM   #5 (permalink)
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I agree with Eboni and Drongle's tips and add that it's pretty easy to be low LI. I've discussed elsewhere that I don't feel that should be the only metric for good quality. It's quite easy for people to use a crazy high detail top level model and cheat the rest. It's pretty annoying and doesn't do much to help the public perception that mesh is laggy.

As an aside, that nail polish rack is 76758 triangles close up and doesn't drop until you're zoomed about 20m away. Ouch!
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Old 10-17-2013, 03:44 PM   #6 (permalink)
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Quote:
Originally Posted by Aki Shichiroji View Post
that nail polish rack is 76758 triangles close up and doesn't drop until you're zoomed about 20m away. Ouch!
I thought that when there were lots of triangles, it would make the LI high, but it says its only 1 prim.
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Old 10-17-2013, 03:49 PM   #7 (permalink)
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Quote:
Originally Posted by Sherrie Melody View Post
I thought that when there were lots of triangles, it would make the LI high, but it says its only 1 prim.
Therein lies the problem.

I could be wrong but it looks like only three LODs were used for that model. Two of them are probably the top level model THe top two levels are probably the top level model. THe next drop is around 155 triangles and removes the bottles entirely. THe last one uses 8 triangles, probably one for each material face being used.

The current LI system allows people to drastically reduce their LODs despite having a high detail top level model and get around the L$ and LI cost of using the top level model on its own.

Last edited by Aki Shichiroji; 10-17-2013 at 04:03 PM. Reason: Clarification
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Old 10-17-2013, 04:43 PM   #8 (permalink)
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Originally Posted by Aki Shichiroji View Post
Therein lies the problem.

I could be wrong but it looks like only three LODs were used for that model. Two of them are probably the top level model THe top two levels are probably the top level model. THe next drop is around 155 triangles and removes the bottles entirely. THe last one uses 8 triangles, probably one for each material face being used.

The current LI system allows people to drastically reduce their LODs despite having a high detail top level model and get around the L$ and LI cost of using the top level model on its own.
So even though this has 1LI, it is a lag producer on the viewer, is that right?
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Old 10-17-2013, 04:48 PM   #9 (permalink)
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Quote:
Originally Posted by Sherrie Melody View Post
So even though this has 1LI, it is a lag producer on the viewer, is that right?
Basically, not all 1LI items are the same. I'm sure someone could make another 1 LI nail polish stand that would be far less laggy on your viewer. It's just unfortunate that most people directly equate low LI with something that is efficient and which does not present a significant amount of resource load on others' viewers, when this isn't necessarily the case.

If you are consciously trying to create a low viewer lag environment, it's important to weigh the complexity of the item you want to buy against how significant that item should be within the environment, along with whom the display is for.
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Old 10-17-2013, 04:57 PM   #10 (permalink)
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Quote:
Originally Posted by Aki Shichiroji View Post

If you are consciously trying to create a low viewer lag environment, it's important to weigh the complexity of the item you want to buy against how significant that item should be within the environment, along with whom the display is for.
Just to add - to do this, it's best to shop for mesh items in world, or at least check a demo. You can check how many triangles an item has by selecting it and opening the Render Info menu, under 'Develop> Show Info' menu in your viewer. You'll get a column of white text on the bottom right corner of your screen. The third last line will indicate how many triangles are in your selection, along with how many verts it took to make those faces, how much memory it takes to draw the item, as well as how many objects are selected in the linkset.
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Old 10-17-2013, 05:06 PM   #11 (permalink)
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Thanks Aki. I didn't realize I could get that kind of information from the viewer.
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Old 10-17-2013, 08:45 PM   #12 (permalink)
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Quote:
Originally Posted by Aki Shichiroji View Post
The current LI system allows people to drastically reduce their LODs despite having a high detail top level model and get around the L$ and LI cost of using the top level model on its own.
Yes. That's because it is based on the resource use (lag effect) on average for randomly distributed viewers over the containing region. That implies most will be seeing only the lowest LODs. So for someone spending a lot of time close to the object, who is always looking at the high LOD, it does not represent the resource use well at all.

It is especially misleading to use the LI as a guide for attachments where the wearer is concerned, as they will always see only the high LOD (unless it's very tiny). It's still quite bad for estimating attachment effects on other residents too, because avatars congregate, so that their distribution is very far from random.
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Old 10-17-2013, 09:22 PM   #13 (permalink)
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Thank you. This is the kind of information I was interested in. It is kind of disappointing to learn that some people "cheat" the system and that is one of the big factors as opposed to what I thought was going on -- effective design practices I was unfamiliar with. On the other hand, I would only use an item like the nail polish rack on my personal property where I would be the only person (or one of very few people) affected by any lag, etc. But now I know what to look out for if I'm decorating a public space.

Since I will likely not be selling anything I make, I'll experiment with some of the things in the tutorial. I can see manipulating more of these types of things where I'll be the only one affected.

Thanks for all the info and clarification!
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Old 10-17-2013, 10:39 PM   #14 (permalink)
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Originally Posted by Drongle View Post
Yes. That's because it is based on the resource use (lag effect) on average for randomly distributed viewers over the containing region. That implies most will be seeing only the lowest LODs. So for someone spending a lot of time close to the object, who is always looking at the high LOD, it does not represent the resource use well at all.

It is especially misleading to use the LI as a guide for attachments where the wearer is concerned, as they will always see only the high LOD (unless it's very tiny). It's still quite bad for estimating attachment effects on other residents too, because avatars congregate, so that their distribution is very far from random.

I miss guidelines of "how many vertices is too much for what" coming from LL. Like, if it's an attachment, should it be 200-300 tri's, or is 3000-4000 ok too?

For things that are rezzable, the first LOD really barely counts, so it's quite easy to make 1 LI items, and then have them degrade into goo (or vanish) from distance. Although in a way that could be fine- indoors things don't need LOD for distance viewing.

Ack this is giving me a headache. I'm currently making mesh ears everyone will hate (for too many tri's).
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Old 10-18-2013, 12:54 AM   #15 (permalink)
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Part of the impact depends on what you are creating, clothes can have a relatively high level or tri's at the highest LOD but can use much lower ones for the lower LOD since they will have (in reality) the detail fade at relatively short distances. I am not sure about physics on clothes since I build buildings. Physics can have a major impact on larger items, but in the case of the nail polish rack I suspect the physics was a cube with very low LOD which would have very little physics impact.

The other thing that can kill a viewer is using too many too high definition textures which can kill a frame rate even thorough they don't register and are not figured into the mesh impact calculations. Someone who is both careful with the intermediate and physics LOD and also uses reasonable textures for the size and type of object can get a highly detail;ed object with a low LI.
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Old 10-18-2013, 04:25 AM   #16 (permalink)
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My own list (with potential repeats from previous posts):

* Remove unseen faces

* Do not worry about smoothly blending pieces of mesh. Merging by welding vertices of a mesh to the surface vertices of another can drastically increase the amount of faces on the surfaces, due to the limitation to triangle connections.
EXAMPLE: If you make a handle for a mug, just stick the ends of the handle into the side of the mug, and turn them into a single object. You're done. Keep it simple. No need to beautify things nobody will notice.

* Personally, I always set the lowest LOD to '1' on upload. This drastically reduces LI, does not matter for rigged mesh, and isn't really noticable otherwise either.

* Build a custom, simple physics shape to associate with an objec, instead of generating a complex one. For objects where it doesn't matter, or attachments, just choose 'lowest' as the physics LOD.
EXAMPLE: I made a rigged latex suit from my shape's mesh. It covers most of my body except hands, feet and parts of the head. It's smoothly subdivided, increasing the vertex count, and has materials support. It's 2 LI when rezzed in-world, because it has an uterly simple physics shape, and the lowest and low LODs are '1'.

* Make your object not too high poly. Use a low poly model, then copy it, make a high-poly model from it and create a tangent normal map from the two. This allows you to make a low poly model look much better.
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