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Hello!

After much research and trial and error, I have learned how to use Blender 2.76 to create mesh objects. I am a Builder in SL, I specialize in creating houses and texturizing. I am also wanting to create furniture as well. It has always been my dream to create low prim builds and it seems to me that meshing is the way to do this.

I've recently tested my skills on a very simple pallet bed but when I looked to upload to SL, I seem to have done my exportation incorrectly. I have searched all over the internet on how to resolve this issue but all I am finding is information to old versions of blender and add-ons to them.

Does anyone know how to use Blender 2.76 for mesh building? Do I need to locate an add-on to help and what?

 

Thank you!

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You don't need an add-on (thanks to Gaia). Here is the simplest process: Select only your object; File->Export->Collada; After selecting folder and typing filename, Click the "Operator Presets" button half way down on the left side and choose "Sl + OpenSim static" - these options will work foe most unrigged objects; Then click the "Export Collada" button at the top right.

If you have done all that and still have problems, then we probably need more information to identify the cause(s). At least we need to know exactly t what point your upload fails, what are the symptoms and any error messages? Do you have the same problem if you try to upload the default Blender cube?

 

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It would be great to have some more details.

What went wrong?

Did you fail to upload your mesh to SL? Did you get any error messages? Was the prim count/land impact different from what you expected? What format did you use to upload to SL? Did you build/use LOD's? Stuff like that would be most helpful!

There should not be any addon needed to export out of Blender into SL. 

There are tons of tutorials on You Tube on using Blender to create for SL. Some interface changes a bit over time, but not that much that you would not be able to work with those tutorials. Just the versions before 1.5 (if I am correct, it may be 1.4, lol) are very different. I would not recommend using those unless you already know your way around Blender!

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Hi :)

I'm going to complicate your Export a little by suggesting that you need to export two meshes :smileysurprised:

The second mesh is going to be the Physics/collision mesh. ( I am assuming your Pallet bed is a single mesh object) Using your visual mesh as a guide create a new mesh Object in Blender consisting of two boxes like in the image below. Leave a little space between each box.

Exporting:

  In Object mode select only your Pallet bed mesh and export as described in steps 3,4 and 5 below :



 Next deselect your Pallet bed mesh and still in Object mode select only the Physics mesh. Repeat steps 3,4 and 5 for the Physics mesh.

You will now have two .dae files named something like Pallet bed.dae and Pallet bed PHYS.dae

 

Uploading:

To upload your mesh, from the Viewer header open the Build menu and choose Upload > Model. Navigate to where ever you saved the Pallet bed.dae file and and choose that. When the Uploader panel opens you will find it has been loaded into the High slot of the Level of Detail tab. (step 7 below):



 

Next,  open the Physics tab and in Step 1 select the From File option and then load up the Pallet bed PHYS.dae file.

In Step 2 of the physics tab hit the Analyze button.

Hit the Calculate weights and fees button then the Upload button.



 

Once you have your Pallet bed mesh rezzed inworld there is one last thing to do: change the Physics Shape Type to Prim.

 

Note: The box type physics mesh is fine for small objects like pieces of furniture but later when you come to create larger objects like buildings you will find that you can achieve lower Physics weight costs for Land Impact if you use a second method that uses planes instead of boxes. This  type of Physics mesh is not Analyzed in Step 2 of the Physics tab in the  mesh uploader.

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Beautiful job as aways, sweetie!

NOW -- I read though this even though I knew it LOL because long ago you tried to explain to me WHY you want to analyse mesh and when you do not. 

I am still (successfully) using Drongel's analyse method (perhaps he only talked about that for simplicities sake as it was three years ago and I was VERY VERY NEW.)

 

Anyway, I typically use boxes on buildings and my physics costs are way way below my download or server costs. Everything works fine and amazingly on my last house it seem like some of the early physic issues on houses from a few years ago have been fixed (very happy about that).

 

I am also getting smarter from so much building. So can you point me to that "why analyze" post maybe? I suspect I am not the only one in town that hasn't a clue between the difference. It may not matter to me as I am a simple gal and items are low poly and not terribly complex, but I might be able to grasp the point now (it seems to take me a few months before I get things mentioned here -- not unusual).

 

Thanks so much. Always appreciate your input.

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Hi Chic :)


Chic Aeon wrote:

......... So can you point me to that "why analyze" post maybe?

Not sure which that would be .......... :smileyfrustrated:

Why analyze?


The short answer is, because when it comes time to create your physics mesh you “choose” to use the box method and that method is meant to be analyzed. Not a very good answer ……….


A slightly different question could be, what’s the difference between Analyzing and not analyzing the physics mesh?


When you hit that Analyze button you are asking the uploader to convert the mesh that you designated in Step 1 of the Physics tab into a collection of convex hulls. By using non overlapping boxes in your physics mesh you are making this analysis and conversion easier for the uploader. The little space left between boxes allows the uploader to easily recognize each individual box as a convex hull. Job done. Using non overlapping boxes usually results in a physics mesh very similar to the physics mesh you gave it.


Giving the uploader a physics mesh made up from overlapping boxes would makes its job more difficult and could result in it "seeing" and then creating convex hulls where you don’t really want them to be.

What happens if you don’t analyze your physics mesh?
If you don’t ask for it to be analyzed ………… it doesn’t get analyzed. Apart from converting quads into triangles the uploader leaves it EXACTLY as it is. The result is the physics mesh of the object will be exactly as you created it. Sounds good. :)


Now you are still asking , Why bother to analyze the physics mesh I created using the box method ?


I’m not 100% certain here ……….. Physics engines can be coded to recognize certain common primitive shapes like box shapes or spheres etc. When they come across a box shaped physics shape inworld they know already how to treat it so the load on the Physics engine is small. When it comes across a more complicated shape it has to do a lot more calculations to work out how it physically interacts with other objects. The load on the Physics engine will be higher. The lower the load the smoother things will run.
Second Life uses the Havoc physics engine and what I think is that it has been coded to “recognize” the convex hulls physics shapes that the uploader created and so has less calculations to preform every time it has to deal with them inworld. (As Drongle is away dealing with RL boxes maybe Arton, if he reads this could step in and give a better explanation of why convex hulls are used ).


If you don’t analyze this type of physics mesh the Physics will have to be calculated for each face/triangle every time those triangles interact with other objects (triangles) inworld. Using the box method you may have a lot more faces in the physics mesh than is needed. This means more physics calculations to perform than necessary. More load can mean more lag.
Also you may have small, thin faces on some of the boxes which would increase the density of triangles per meter to be calculated……… for example if an avatar can interact with many triangles at a given moment this means a lot more physics calculations will have to be made.
This is why when you are using the other method, the Planes/triangle method for creating your physics mesh, rule number one is, avoid small thin faces. This type of physics mesh is designed not to be analyzed so every triangle in the physics mesh will have to be calculated for physics purposes.


The uploader will thank you for using large faces/tris in this type of physics mesh by lowering the Physics cost but will penalize you by increasing the physics cost if it finds small thin tris. When rezzed in world if you increase the size or a mesh object using non analyzed physics you will notice the physics cost will decrease because you are increasing the size of the triangles used in the Physics mesh.


A couple of years ago I did some experiments to check how physics cost vary depending on which method was used when making the physics mesh and will reuse the images here.


Image 1 is a simple mesh building
Image 2 is the physics mesh for that building using the box method. ( Just a note: the boxes are only coloured differently to emphasize the use of individual boxes ).
Image 3 is the physics mesh for the building using the planes method. ( Again the faces are only coloured to show that the separate planes are not connected ).

 

Image 6 shows the land Impact costs for the building when using the Analyzed box method physics.
Image 7 shows the L I costs for the building when it is using the non analyzed planes method.



In the case of image 6 it is the Physics cost that is being used for the final LI cost. When the uploader creates the collection of convex hulls the physics cost for each hull is always 0.36. It found and created 8 hulls in the phys mesh, 8 x 0.36 = 2.88 rounded up to be 2.9 costs for physics.


The number of hulls can quickly add up so if you do find your physics cost dominating the download costs then try using the planes method and not analyzing .

For some reason the quality of the images are not very good especially the one showing LI costs when loaded from my picture library here so ask you to check the earlier post, message number 4 here:

https://community.secondlife.com/t5/Building-and-Texturing-Forum/thinner-walls/m-p/2861020#M12540

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Now you are still asking ,
Why
bother to
analyze
the physics mesh I created using the box method ?

 

No, I always analyze because Drongle TOLD me too long ago LOL.   So I never asked. Had to smile at that.

 

The uploader will thank you for using large faces/tris in this type of physics mesh by lowering the Physics cost but will penalize you by increasing the physics cost if it finds small thin tris. When rezzed in world if you increase the size or a mesh object using non analyzed physics you will notice the physics cost will decrease because you are increasing the size of the triangles used in the Physics mesh.

 

So that is why the hills you made me a few years ago INCREASE in land impact when made smaller
:D
.  Ah ha.

 


So the GOOD news is that I understood what you said this time.  So far all my builds have come in WAY lower for physics than download and I have always used boxes since that is what I was "taught". For what I do I am guessing they will be the best.

 

THANK YOU!

 

 

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"because Drongle TOLD me too long ago"

I have to guess this was for small objects*, for which that is the method giving lower physics weights. As Aquila pointed out, This is not the case for object consisting only of large triangles, of which the most common are buildings and walkable landscapes. For those, it is much better to use triangle-based shapes - that is to say, avoiding analyze.

Note: Aquila's statement that the physics weight is 0.36 per box is true for simple boxes with six quadrangular faces. It comes from the fromula 0.04 x (number of vertices + number of hulls), which is provided in the wiki documentation. The two numbers are shown in the uploader after you analyze. However, that formula is only accurate for certain shapes where there are exactly three faces meeting at each corner, such as simple boxes and cylinders. In other cases, the physics weight is different from the value obtained by applying that formula.

* do you remember where I told you?

 

 

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I have read over this and I notice a faint light in the darkness now. It would help if I knew what a hull was. Something to do with boats I think, right?

I am going to keep reading till I understand it. May take a while.

Anyway, many thanks, Aquila and Drongle.

 

ETA I never quite understood why my simple arched wall was 8000 LI when set to Prim.

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Long post with replies to several previous ones... sorry.

 


Pamela Galli wrote:

I have read over this and I notice a faint light in the darkness now. It would help if I knew what a hull was.

A bit off topic but:

https://en.wikipedia.org/wiki/Convex_hull ;)

 

The simplest explanation I've heard of what a convex hull is, is that it's a shrinkwrap around the object. That makes a much simpler shape of course since it eliminates all the little bumps and indentations.

 

It's important to differentiate between the convex hull physics shape we can use inworld and the convex hulls we get when we analyze the physics shape in the uploader though.

The convex hull physics shape we can select in the builder window is a single one encompassing the entire object. When we upload a mesh, we - or the uploader - can split it into several parts which each gets its own convex hull.

 

Usually when we use analyzed physics in the uploader, we want to make it from clearly separated cubes as Aquila suggested. That's the easy way out, you know exactly what the physics weight will be (0.360 for each hull and it doesn't change when you resize) and you have a pretty good idea how the physics shape will end up. Better watch out though, sometimes the uploader gets sneaky and tries to add some extra hulls even if you tell it not to. I've even had some meshes where I had to do exactly the opposite of Aquila's advice - where the only way to get the correct number of hulls was to make a complex merged physics dae and get the uploader to split it up.

The cube isn't the only convex hull though. Any polygon with no angles pointing inwards is a convex hull. Unfortunately, the uploader doesn't know that and it can't handle all possible convex hulls. My experience (Aquila or Drongle may correct me here) is that it can usually handles hull shapes with "unbroken" sides facing at least one axis but it faints when it sees a real three dimensional complex convex hull.



Chic Aeon wrote:

No, I always analyze because Drongle TOLD me too long ago LOL.


I think that was good advice, even though Drongle denies it now. You can sometimes save a lot of LI by using unanalyzed physics and analyzed physics also has some disadvantages for walkable surfaces (personally I probably wouldn't use it for the palettes in Aquia's illustration for example) but unless you really understand how those physics shapes work, you have to be prepared for a lot of trial and error and it might not be worth the time and effort.


Back to topic:


Dyson Indigo wrote:

It has always been my dream to create low prim builds and it seems to me that meshing is the way to do this.

I'm always a bit scared when people talk about mesh as "low prim" because there are so many ways to cheat to achieve that. You can make very simple mesh and overload it with lots of laggy custom textures for example (I've seen fairly small houses with render weights of 30 000, 40 000 even 50 000!!!). Or you can butcher the LOD models.

The latter is the favorite method among people who pretend to be mesh makers because it's so easy, you just have to reduce the numbers for the LOD models in the uploader.

Here is my standard for good mesh:

With RenderVolumeLODFactor set at 1:

  • an indoors objects still looks good when viewed at 25-30 m distance
  • an outdoors object looks good at 128 m distance

(what do I mean by "looks good"? Ummmm... that's a good question, glad you asked ;) )

 

Physics depends on what kind of object it is of course but for a house:

  • All walls must be perfectly solid.
  • All floors must be walkable - with no noticeable hovering above the surface and certainly no sinking into them.
  • Roofs must be walkable although I'm willing to accept a little bit of hovering and even sinking on a sloping roof. (Edit: except thatched roofs of course, you want quite a bit of sinking into them.)
  • It must be possible to rez items upon all major surfaces that aren't vertical.
  • Staircases can have ramp physics but if so, it must be set to minimize hovering and sinking.
  • Large dormers and bay windows are of course spaces it should be possible to walk into.

Others may have lower quality standards, but me, I flatly refuse to accept any mesh that doesn't meet these requirements as good quality.

If you want to make quality mesh with low land impact, you'll need to put a bit of effort into it. Not only do you have to make a separate physics model as Aquila mentioned but you will also need to make LOD models manually. The uploader isn't able to help you there. It generates the LOD models by removing triangles from the model and there's simply no way it can know which ones to keep and which ones to eliminate. So if you use autogenerated LOD models, you either end up with lots of holes in the models or unnecessarily high LI because it keeps lots of unnecessary triangles. Tools like Blender's decimate and limited dissolve functions, Mesh Studio's resolution settings etc. can help you on the way but to make truly efficient mesh with good quality and low land impact you'll have to do most of the decimation manually. It's worth it though, if only for the satisfaction of a job well done. :)

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"my simple arched wall was 8000 LI"

If you take a mesh and roll it about on a flat table at every possible angle, some of its vertices can never touch the table because they are in depressions in the surface. If you eliminate all such vertices, so that every remaining vertex can touch the table at some angle, the remaining vertices constitute the convex hull of the mesh. In SL, the hull is represented as simply that, a list of vertices, although it is more commonly represented elsewhere as a surface containing those vertices. It is much easier for a physics engine to work out collisions with a convex hull than with a general mesh that can have concavities. The convex hull is often described as the shape of a shrink wrapping of the mesh, but that is not quite accurate, because shrink wrapping of 3D objects can have saddle points (opposite curves along perpendicular tangents), while convex hulls cannot. 

A convex hull is not always much simpler than the mesh it is generated from. For example, the convex hull of a sphere is the whole sphere, because it already has no concavities. So using "Analyze" does not necessarily give you low physics weights. You still need to use a simplified mesh to obtain a lower physics weight.

You can now experiment with convex hulls in Blender (7.6b)  - in edit mode, press space bar, then type convex hull and click the button that appears. That may be the best way to become familiar with them. Indeed, you can use this operation on selected subsets of vertices to make a set of convex hulls that could be the starting point for your physics mesh suitable for "Analyze".

To return to the main subject - there are some bugs in the physics weight calculation for triangle-based shapes that can occasionally lead to very high (thousands) physics weights even when there are no small triangles. There was a series of threads where this was discussed a long time ago ( search for "physics weight episode").

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You are quite right in saying that the "Analyze" doesn't work optimally for a lot of meshes. Most often, supplying a set of non-overlapping hulls avoids problems, but I don't suppose it isinfallible. On the other hand concave meshes and overlapping hulls very often lead to very poor shapes. It's also often worth experimenting with the differences between "surface" and "solid" decomposition.

I thought of another couple of reasons I may have advised against un-analyzed (triangle-based) physics shapes, even for walls. First, with double-skinned walls, it is possible to penetrate one of the skins and then you get stuck beteween them, trapped in the wall, which is not very nice. This can't happen with convex hull-based (analyzed) wall, because the physics engine always knows whether you are inside or outside. If you do get inside, it will nudge you out again. So you can't get stuck. Secondly, there are some strange collision effects that can happen with triangle-based shapes. For one thing, they are easier to penetrate (or fall through if it's a floor), especially when moving fast, and usually easier fro one side than from the other (I have never understood that). In certain circumstances, it's possible for that asymmetry to be extreme, so that you can make one-way doors, or even an invisible one-way cube that you can walk into easily but never walk out of. So generally, Analyzed walls may be a bit safer, although they are more expensive in physics weight for large walls. Then of course, there's the bugs with triangle-based physics weights, as mentioned above.

 

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Drongle McMahon wrote:

Most often, supplying a set of non-overlapping hulls avoids problems, but I don't suppose it isinfallible.

I think there's a new quirk with the uploader there. Sometimes it splits non-overlapping hulls but not overlapping joined ones. I've seen that twice recently and it has never happened to me before. I sent some example files to you and to Aquila in case you want to have a look.

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Yes. Tried a few versions of these. Looking at the one that splits into 4, what happens is that the bottom quad of the small box facing the larger box gets split into a separate hull. No idea why that happens. It only happens if you leave the default "Surface" setting for "Method". If you set this to "Solid", then you get the expected three hulls. I generally use "Solid", although this sometimes works the other way round. You can also get three hulls if you use "Simplify" with "Method" as "Retain%" and "Reatain" set to 87% (and lower), while leaving "Surface". I think using "Solid" is the best advice, and then using "Retain%" if you still have problems. These willonly work reliably, though, if you do have non-overlapping convex hulls in you physics mesh. Otherwise, you can get all sorts of horrible effects. I guess that's where the advice is most important, more than for the default case, but for the desired result if you use a bit of "Simplify".

The internal code for the decomposition into hulls is not accessible, as it's part of the Havok engine, not open source. It certainly has some strange behaviours, and it can change with new versions of the Havok library get used. So it's quite possible that there have been changes, and that it may change again.

 

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