Questions: trying to understand Physics shapes

[Siddean Munro]

Hey all, I have a little model I'm trying to upload using a custom physics shape for the first time ever.  I am having a couple of issues and want to determine if it's something I am doing, or a viewer bug?  Or what else is going on?

Basically - why does the calculate weights button disappear when I select my physics model?  It seems to be fine when I go through the physics tab and generate a physics shape there, but I'd really like to learn how to create a physics shape myself.  It was previously 28 tris, kind of cube shaped with an extension for the back of the chair, and a complete model with UV, I then deleted a bunch of faces so it's the 6 tri thing you see above but neither model worked.  Do I even need to create a UV with a physics shape?

[Medhue Simoni]

You don't need a UV map for the physics. I also had an issue today uploading a physics shape and not getting the upload option. I went and downloaded the latest Mesh project viewer and it worked in that viewer.

[Siddean Munro]

Thanks for the reply!  I'll go download the project viewer because nothing I do seems to be working  It has to be easier than this...

[Kwakkelde Kwak]

You never needed a UV map for the physics. What did change (and possibly is "unchanged" in the latest project viewer) is the fact the physics shape needs one of the materials from the visible models. This wasn't the case before V3.1 and it's without a doubt what's causing your problems. LL admitted it didn't make a lot of sense, so it's very possible they changed it back.

[Siddean Munro]

ooh I did not know that.  Anyway I managed to muddle it out, not sure exactly how it happened between viewers crashing, disappearing from my PC altogether, and between either the browse button or the calculate button vanishing, and multiple restarts.  Surely I missed some incantation or sacrifice to some oldworld god somewhere along the line!  :matte-motes-sour:

I'll try again with the material assignment, thanks for the advice!

And even though it said it had a Land Impact of 6, by the time I got it in and scaled it down, it works out to be 2  Should prolly do the scaling in Blender first.

[Kwakkelde Kwak]

The Prim impact is measured by a number of factors, including scale, since the smaller it is, the less distance it takes to flip to a lower LOD, which makes the render cost lower. That's why it went from 6 to 2. Best is to scale in blender yes, that way you will see right away what it will cost inworld. If this is inconvenient for some reason, you can set the scale factor in the upload menu, third tab, next to physics ( I forgot what it's called). I do this for a truck I am working on. I build it scale 1 to 1, so it makes sense when I build it, then I set the upload scale 20% higher so it matches SL better. (Not 50% or even 100% which seems to be the case for some 4 meter wide and 10 long cars on the grid:) )

Oh duh, you have a screenshot of the menu, the scaling is in "upload options"....

[Siddean Munro]

Aaand on your advice, added the physics shape to a random material from the main mesh, scaled the model down in Blender so it didn't come in 20 metres high, restarted SL cos the browse button didn't highlight when I selected physics from file, and uploaded successfully with a server weight of 0.6 and a Land impact inworld of 1 :D  Thanks!

[Kwakkelde Kwak]

There's this weird bug I have been experiencing with that physics from file button in the beta viewer I'm using..not sure if it's the latest viewer, but anyway... Click it once and things go grey, click it again and it works... maybe that's the case for you aswell...I'm happy you got it uploaded correctly and I bet so are you

Oh and i think if you link three together they will only cost 2 prims on your parcel...

[Siddean Munro]

Yea I have it linked with 24 regular box shaped prims filled with all kinds of funky scripts for a HUD and it costs me... 24 land impact  The box is the root prim.

[Kwakkelde Kwak]

Hmm root prim or child prim shouldn't make a difference as far as I know, just the fact there's a mesh in the set. I think if you had left the scripts out of the boxes ( which is ofcoursenot going to happen, that's why you have those boxes in the first place) you would be looking at something like 12 prims instead of 24. Size should matter, but I've seen my boxes count as less than a prim at house sizes. These were basic boxes though, no hollow or twist modifiers applied. Anyway, for prim efficiency you did well I guess:) you got yourself a free chair.

[Medhue Simoni]

You can also scale the model to whatever size you want right in the uploader. It's important to have the right size or you are not seeing the correct land impact score.

As far as material, in 3ds Max, I have to attach the physics model to the mesh, which automatically applies the material to the physics model. From there, I have to select the physics model by element and detach. This is just how it works in Max, I have no clue about Blender.

[Kwakkelde Kwak]

No you don't have to attach and detach in max, although this trick solves a lot of little pains quite easily, very true. All you have to do is assign one of the materials used in your model to your physical shape and it's fine. As far as max is concerned you end up with the exact same thing.

[StoneDwarf]

Thanks for pointing this out, Kwakkelde. I had the same problem as Siddean had on random moments and wasn't sure what caused it. 

I changed the materials and it worked.

Cheers,

[Siddean Munro]

I am not sure how I would make a 24 prim linkset into 12 Land Impact just by taking the scripts out, my understanding is that legacy/SL prims still count as 1, which is why I have never really understood all the yelling about scripts doubling land impact or whatever.  I played around with the LOD setting in my chair, added a few more cubes for my HUD using various scripts that move prims around, send colour, texture, size and position commands back and forth to an attachment I am wearing, added a sit script and animation and it's still only 35 land impact, even when the chair itself went from 1 to 3 with the LOD changes that now mean it doesn't degrade until you're quite far away.  To be clear that is 33 actual SL prim cubes (I counted), and one 3 LI mesh chair with 3 texture faces and 512 textures on each.

 

I did a test with a linkset of 6 prim cubes in a linkset:

6 cubes in one object that equals 6 Land Impact.  

Put scripts in each of them - 6 Land impact.  

Made them HUGE - 6LI.  

Made them Physical - 6LI.  

Added my 3 LI chair to them - 9 LI when softlinked,  7 LI when hardlinked, physical or not, didn't matter

Made that linkset HUGE, as big as it would go without snapping back to 64m - 38 LI  Which to be perfectly honest, isn't that unreasonable, considering we don't have 64m tall avatars who would ever use a chair that size

 

So anyway, that's just been my experience all along with the exception of that teething period when the calculation was being tinkered with.  I have never, ever noticed that adding scripts to prims or meshes does anything to Land Impact, other than occasionally adding 1 to the final number.  That's not to say it doesn't, just that I have never had it happen to me, not for want of trying!

[Kwakkelde Kwak]

To be honest it hasn't happened to me either...hehe

But I read (sorry forgot where, but recently on the mesh forum for sure) that adding scripts adds a multiplier to the server costs of a mesh, which makes sense. The server cost of a box isn't that big ofcourse so one would probably not notice it in land impact. The landimpact not going up by stretching the object doesn't make sense to me, but this could also be because of the simplicity of the object. I'm not curious enough to do extensive testing on this, so I hguess I'll never know the details unless someone posts them:)

Still 24 landimpact sounds high for 24 boxes, even if this means you got the chair in the set for 0 prims (if you want to look at it that way)

[Drongle McMahon]

Sid & Kwak

Try this: rez a default cube; shift drag until you have 24; link [LI* = 24]; check Edit Selected and select one of the linked cubes; on Features tab, set it to Physics Shape Type Convex Hull [LI* = 12]; on Contents tab addnew script [LI* = 24]; delete the script [LI* = 12]; with all selected, make Physical [LI = 24].

* the display update is delayed for some of these (bug). You have to deselect and reselect to see the changed value.