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How reliable is mesh on Beta Grid?


Six Igaly
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I mean, I do my best to (learn to) create decent mesh objects. So I read a lot and practice a lot, just as I'm doing today. I was about to upload a simple object when I realised I was on the main grid, so I logged off and re-logged on the beta grid. Then I started the upload process again only to find out the numbers where totally different then on the main grid, especially the physics weight is very different on both grids. It puzzles me. Here is an image that shows it all. Besides for saving Lindens  I don't see much use for the beta grid to test my mesh like this. Do I miss something?

 There also is a small difference in display costs between my used viewers on both grids.



 

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Are you using explicit LOD meshes and physics? If not, you need to know that the automatic LOD generator is non-deterministic. That means it can generate different results on different occasions for the same input. The default physics shape is generated from the low LOD mesh, unless you tell the uploader otherwise. So the physics weight of the default shape can also vary substantially as the result of the variation in the LOD generator. The only good solution to these efefcts is to make your own LOD and phsyics meshes, which is advisable for other reasons too. If you aren't doing that already, I would suggest you try that.

The download, physics and server weights are now calculated by the server. The beta grid is where LL test changes to the server code. So there is no guarantee that it will always be the same as the main grid. As far as the display weight is concerned, I don't know whather that's calculated by the server or the viewer. You observations would suggest the latter.

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I made my own LOD models and used them. I did not make a  seperate physics mesh ( is this the same as collision model?), that's something I'll try next then.


Drongle McMahon wrote:

The download, physics and server weights are now calculated by the server. The beta grid is where LL test changes to the server code. So there is no guarantee that it will always be the same as the main grid. 

Ok, so basically on the beta grid I can only test the way my models look. Got that.


Drongle McMahon wrote:

As far as the display weight is concerned, I don't know whather that's calculated by the server or the viewer. You observations would suggest the latter.

Ah of course! I guess that must be it!

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If you used your own low LOD, with default physics, then that should have been the same result on both grids for the default shape. If you weren't using the default shape, it would depend on settings. For this model, I would use a simple cube phsyics shape (which will get stetched to fit by the uploader) and click "Analyze", which should always give you a physics weight of 0.36.

"Ok, so basically on the beta grid I can only test the way my models look. Got that."

I wouldn't say that. While it's possible for the weights to be different, it should be very rare, especially as there have been no chnages to these parts of the system for a long time, as far as I know. My point is really just that it isn't absolutely guaranteed. I would still guess that there is some other cause for the differences you saw.

 

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If you used your own low LOD, with default physics, then that should have been the same result on both grids for the default shape. If you weren't using the default shape, it would depend on settings. For this model, I would use a simple cube phsyics shape (which will get stetched to fit by the uploader) and click "Analyze", which should always give you a physics weight of 0.36. 

Ok, will try that next.

I never thought about making a physics shape simply because it is not a building or anything walkable. So what I wonder now, based on what you say, I should always make a physics shape regardless the model?

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Well, it's only necessary from the LI point of view if the physics weight is higher than the download weight. However, it is good practice to always make a simple physics shape in order to minimise the work the physics engine has to do, even if it doesn't save LI (unless, oif course, you are going to set the physics shape type to "None"). It also means you control the physics precisely. It is sometimes surprising to see how high physics weights can be with something like your pillar. Even the convex hull can still have many vertices, and thence a high weight, when it has an irregular surface like the ragged top of your pillar. Only the indented vertices will be left out. Small details have no discernable effect on the collision behaviour, but can greatly increase the physics weight.

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Mm ok, I think I'm getting to understand a bit more and yet I don't at the same time. What stays is that the pillar on the beta grid has a physics weight of 2.5 while on the main grid just a 0.8 (which is better I guess) while it should be the same since I did exactly the same on both grids..uploading the four .dae files and leave the physics tab untouched = default physics (right?).

 

/me wonders if he gets to understand it all before SL comes to an end :smileytongue:

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Maybe the difference comes from the third party viewer, if the mesh was uploaded with that. If it's a 64 Bit version of Alchemy, it won't have the Havok libraries. I don't know if the 32 Bit has Havok even, since I don't use any TPV myself.

The discrepancy in display weight between the 2 viewers is strange enough actually.

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Good point Arton. The Havok library is certainly used for the decomposition when you click Analyze. I guess it is likely used for the default convex hull generation too, although I don't know that for certain. If it is, then that could indeed make all the difference. It's also possible that that viewer uses a higher LOD for the default physics shape. The change from the high to the low LOD in the LL viewer was quite a long time ago, but.... 

However, I suppose that can't explain differences between the two grids, when using the same viewer?

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Drongle McMahon wrote:

However, I suppose that can't explain differences between the two grids, when using the same viewer?

Yeah, the question is, was it the same viewer to do the upload on both grids? And if it was Alchemy on both, who knows what it's doing with the physics shape each time?

Six can bring some light into that indeed.

The discrepancy in display weight puzzles me the most though.

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OK. Just wanted to chime in that I have seen this same odd behavior THIS MONTH on the beta grid (not normally).

 

I use the same viewer on all grids (FS), make my own physics model. Uploaded at the same LODs (this was such a simple thing there was no point in an LOD model).  One item with this behavior was a big tunnel entrance .  On the beta grid, set to prim and so you could walk in and tested, the land impact said  2 (well "I" was in heaven). When I actually got it inworld in SL it turned out to be five. Now I was still happy with five, but still. Odd.

 

I take screenshots of my upload with the snip tool and put it in the file with the mesh (a great habit to get into I think) so I know I am uploading the same settings from my end.

For me (and I haven't been concentrating on this) the mesh comes in higher on Agni than the beta grid. For small things, not enough to matter really, just noticeable.  The tunnel was the biggest difference and by far the biggest item I have uploaded in a long while. Not sure if size has any importance, just mentioning.

I just assumed they were doing something over there and didn't think much about it.

 

PS. I didn't make any computer changes this month like upgrades to viewer (Firestorm) so not a viewer VERSION issue, but could be a "viewer" issue. 

 



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I went to both grids again to upload the model again, with both the viewers. To my surprise the display costs are the same now. Physics are still different. It turned out this is not the grid but the viewer since on both grids the differences are the same.



There is a slight difference in the physics shape too. (Note, again I did not used the physics tab in the uploader, so default physics.) What is really different is the way both viewers display the physics shapes. The model I uploaded with the LL viewer shows way different (transparant with small box inside), this is on both grids

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It is a 64 bit viewer yes..

Your other post: // Yeah, the question is, was it the same viewer to do the upload on both grids? And if it was Alchemy on both, who knows what it's doing with the physics shape each time? //

I did it again to be sure.. display weight is the same now..( I guess I goofed up myself somewhere yesterday)

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I take screenshots of my upload with the snip tool and put it in the file with the mesh (a great habit to get into I think) so I know I am uploading the same settings from my end.

 

I'm not sure about what to do with the settings, I mean, there are not much settings to remember IMO. Just pick the same files to upload. But then again, I'm still a noob mesh wise, I have some stuff to learn yet. Besides that, it is a good habit, way healthier then one of my habits :matte-motes-nerdy:

 


For me (and I haven't been concentrating on this) the mesh comes in higher on Agni than the beta grid. For small things, not enough to matter really, just noticeable.  The tunnel was the biggest difference and by far the biggest item I have uploaded in a long while. Not sure if size has any importance, just mentioning.

 

As you can see, now that I've used my own physics shape (simple cube) on both grids with both viewers, the model's numbers are all the same.

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Six Igaly wrote:

So what I wonder now, based on what you say, I should always make a physics shape regardless the model?


Yes, as Drongle already said, make it a habit to always make a physics model. Except if you want the phsyics to be exactly identical to one of the four LOD models of course.

Under no circumstance upload without specifying a physics model at all. Make your own "standard" physics model(s) instead, you onyl have to do it once, it only takes a minute or two and it will reduce the physics weight significantly.

As far as I know it doesn't really matter if you analyze or not when you use a simple cube as physics model. The physics weight seems to end up at 0.36 in either case. However, for objects that are going to be phatom anyway you can get it even lower if you want, use a single triangle aligned to face one axis directly and you get the physics weight all the way down to 0.2.

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Six Igaly wrote:

It is a 64 bit viewer yes..


The reason why a 64 bit viewer won't have the HAVOK libraries is simply that they don't exist in a 64 bit version and without them phsyics shapes can become a bit unreliable. So always use a 32 bit viewer for mesh uploads. And also use a Second Life-only viewer. Apparently there are some licensing issues that means the viewer creators are not allowed to include the libraries in viewers with default access to other grids too. (I never understood the reasoning behind that btw, partly since those libraries shouldn't make any difference at all on a Bullet based grid, partly because HAVOK libraries or not, it's dead easy for the user to reconfigure any viewer (even the SL viewer) to work on any grid.)

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Can't say much about how the physics shape dispolay works in the Alchemy viewer. In the LL viewer, you can see differences between the uploads with the two viewers (assuming that's what each pair is). I 'm not sure which is which, but I can guess from what I know about the default convex hull shape generated by the LL viewer. This is always shrunken inside the visible mesh by a small amout (a fixed proporttion - details in older threads here). So I would be failrly confident that the ones where that is evident are the ones uploaded with the LL viewer. We can then see that the shape uplaoded with the other viewer is different, as it fills the whole space. That doesn't really explain the difference in phsyics weights though. They bot seem to preserve quite a lot of vertices from the irregular top of the pillar. You might see differences that could explain the difference if you can look very closely. Unfortunately the convex hull display doesn't include the vertices. So it's difficult to see.

In your later post, I guess you have used the cube physics shape, because we can now see the expected simple box. In this case, the LL viewer does not shrink the shape. The physics weights are 0.4 (rounded up from the expected 0.36). This is almost certainly acceptable, unless you need some detailed physical interaction with the irregularities at the top of the pillar. If you clicked "Analyze", then you will have this shape whether you set the type inworld to "Convex Hull" or "Prim". This is because the uploader (LL) will use the phsyocs mesh provided to make the default convex hull. In the case of the cube, the "Analyze" will then produce exactloy the same convex hull. If you don't press "Analyze", then the "Prim" type shape will be  a triangle-base shape. Thje default convex hull will still be the same, but if you set it to "Prim" it will use the triangle-based shape, and for an object this size, that may have a higher phsyics weight. You can see the edges of the triangles in the physics shape display of triangle-based shapes.

The two most important things you need to remember about physics shapes are, first, that for each object the phsyics shape will be stretched/squashed to fit the bounds of the visible mesk, and, seconds, that you need one physics mesh object for each visible mesh object. From now on, these should obey the new naming convention: So if an object is called "anobject", its LOD meshes are called "anobject_LOD2", "anobject_LOD1", "anobject_LOD0", and the physics mesh is called "anobject_PHYS". (Just note that this applies to the object names, NOT the file names as stated in the wiki!).

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ChinRey wrote:


Six Igaly wrote:

So what I wonder now, based on what you say, I should always make a physics shape regardless the model?


Under no circumstance upload without specifying a physics model at all. Make your own "standard" physics model(s) instead, you onyl have to do it once, it only takes a minute or two and it will reduce the physics weight significantly.

Good, one thing more I understand now :)

As for the physics as you described, the one triangle, that's something for me to play with..

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Six Igaly wrote:

It is a 64 bit viewer yes..

Your other post:
// 
Yeah, the question is, was it the same viewer to do the upload on both grids? And if it was Alchemy on both, who knows what it's doing with the physics shape each time? //

I did it again to be sure.. display weight is the same now..( I guess I goofed up myself somewhere yesterday)

Thanks, at least that seems to work correctly then across the 2 viewers. :matte-motes-smile:

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