Physics and doorways issues...again

[KyomaraRassan]

I've been reading through the forums to try to understand how to create a simple doorway in blender and upload it into SL so you can walk through the mesh. I've tried a dozen different combinations based on the recomendations here in the forums and i'm still at a loss.

I created this wall as part of a larger building...have uploaded the whole building that i couldn't get into and then started uploading it piece by piece I've used the uploader to calculate and analyze the physic and i've tried creating physics meshes and uploading them from the file on different uploads. I've changed the mesh from convex hulls to prim...and still can't walk through it.

http://i.gyazo.com/1334865aad7695b41b36eabe09302ea3.png

It's a super simple wall...basically just two planes back and front.  I created a single plane going around the doorway and window to use as the physics mesh. You can see in the picture (with the physics shapes and bounding boxes turned on) That the window and doorframe aren't being blocked...but i think the bounding box cuts across the doorway (see the two light green lines at the bottom of the doorway).But how do you then change the bounding box? Is there some trick to creating the planes with the doorways? do i need to use boxes with faces on all sides?  When i uploaded it..i just chose to upload the physics mesh and didn't use Analyze or simplify.  I hope that's enough info to help me get some answers.  I've been tearing my hair out and spending a ton of lindens constantly trying different uploads over it. ANy help would be greatly appreciated.

Thanks

 

[IvanBenjammin]

In most cases, you need closed shapes for physics. You can use open shapes for solid walls to reduce physics weight - for example a curved wall, where you need prim physics to fit the curve - but closed shapes are needed for doorways or holes. I can't be sure, but I suspect SL's physics system is closing the holes anyway, its just a quirk of the uploader than open shapes have a lower LI.

What you can do for walls with doorways is use two boxes on either side, and ignore the lintel above the doorway itself. This keeps your physics weight down, while also allowing taller avatars to pass through a doorway that might otherwise block them. You can't do that with windows, but unless you specifically want to allow objects/avatars to pass through windows your physics mesh can ignore them.

[Aquila Kytori]

Hi

Basically its a bug. when using triangle based physics shapes, that is Not Analyzing the physics mesh in step 2 of the Physics tab in the mesh Uploader, for walls that are less than 0.5m thick. Rezz your wall and increase the thickness to more than 0.5m and you will see that you are able to walk through the opening see link below.

The Bug is that for walls using this type of physics mesh and less than 0.5m thick they are "secretly" (Drongles word for it ) using Convexhull physics and so closed.

All you need to do is either Analyze the simple wall in Step 2 and change to Physics Shape Type to Prim when rezzed or more usually when using Triangle method for physics mesh, don't upload a single wall. Upload several walls together as a single mesh object (so making the over all "thickness" of the mesh object more than 0.5m in all axis.

One of many threads on this subject :    http://community.secondlife.com/t5/Mesh/Making-physics-HELP/m-p/1751753#M18002

 

[Drongle McMahon]

The server closes the holes by switching to convex hull if any dimension of a mesh gets smaller than 0.5M. It doesn't tell the viewer, so the physics shape display does not reflect the switch (that's the secrecy). If you know how to bake and view the navmesh, however, you can see the change there. This behavior is undocumented, although it has been there for a long time. It has recently been reported as a bug (BUG-7681).  However, I suspect it was introduced deliberately, for server performance reasons, and It remains to be seen whether it will be accepted a a bug now that the report is there. It is easily worked around by making sure all dimensions are at least 0.5m, as Aquila says.

[Emma Krokus]

 I've been tearing my hair out and spending a ton of lindens constantly trying different uploads over it. ANy help would be greatly appreciated.

Thanks

 

Did you know that you can use the BETA grid for testing your meshes for free before uploading for real Lindens?

 

 

[Chic Aeon]

You know I KNEW this from long ago and completely forgot about it. Had major (agreed, hair pulling) issues on my latest project. I could not get it to work using custom physics model or even high physics in the uploader (it was a simple build so that worked fine really -- or "could" have). I eventually divided the mesh into two parts and uploaded and then joined in world.

 

Not the most elegant solution but somehow it worked. I had done this many times before and it is possible that this was the issue as I really did forget about it.

 

So thanks to you both for an after the fact explaination. It is difficult doing the physics thing when you have been happily creating in a autophysics world LOL.  

[KyomaraRassan]

Thanks for the link, although I'm still a bit confused.

 

Which mesh needs to be at least 0.5 m thick...the actual mesh wall you want to see or the physics mesh you're uploading with it? If I still want thin walls can I keep the thickness of the mesh and resize the physics mesh to be more than 0.5m, since it's invisbl anyway...before uploading?

 

If I link say 4 walls together in blender that are all say 0.2m thick but overall make a structure that is 10x10m...will that solve the problem? Or will I just end up with one giant box around the whole structure? Do any of the walls, physics or actual mesh need to have enclosed walls or will 2 planes on opposite sides suffice?

 

I know that was a bunch of questions but thanks for the help

 

Also I did not know about the beta grid. How do I use that?

[Drongle McMahon]

Which mesh needs to be at least 0.5 m thick...the actual mesh wall you want to see or the physics mesh you're uploading with it?

The physics mesh is always stretched or squeezed by the uploader to make it fit the bounding box of the high-LOD mesh. So it's the high-LOD mesh thickness that matters.

If I still want thin walls can I keep the thickness of the mesh and resize the physics mesh to be more than 0.5m, since it's invisbl anyway...before uploading?

Making only the physics mesh thicker will have no effect because it will get squeezed..

If I link say 4 walls together in blender that are all say 0.2m thick but overall make a structure that is 10x10m...will that solve the problem?

Yes, provided you make a suitable physics mesh and set physics shape type to Prim. Alternatively, use Analyze to make a hull-based shape instead of a triangle-based shape. The optimum physics mesh required is different for this, and for building-sized objects, the physiccs weight is usually higher, but hull-based shapes are no affected by this bug/feature.

Or will I just end up with one giant box around the whole structure?

Not as long as you remember to set it to Prim.

Do any of the walls, physics or actual mesh need to have enclosed walls or will 2 planes on opposite sides suffice?

The visible mesh(es) will look odd if you leave out the narrow edge faces. For triangle-based physics (no Analyze) the narrow edges' triangles will cause a large increase in physics weight. So you are advised to remove them in the physics mesh. If you go for a hull-based shape instead (Analyze) you may have better control of the shape if you leave the edges in, so that your mesh consists only of non-overlapping, closed boxes.

I know that was a bunch of questions but thanks for the help

Also I did not know about the beta grid. How do I use that?

In the (LL viewer) login screen, use the selection button at the right to choose Second Life Beta Test Grid (Aditi). Then login. When you land, look up Mesh Sandbox in the world map. You will need to retake the mesh upload quiz for Aditi before you can upload mesh there. I hope someone can give you the right URL for that. It has been given in quite a few recent threads. You will start with your main grid inventory, but new items will not be added to the main grid. You will get a fictitious L$ balance to start with, and it should increase gradually.

[ChinRey]

---

Drongle McMahon wrote:

It has recently been reported as a bug (

BUG-7681

).  However, I suspect it was introduced deliberately, for server performance reasons, and It remains to be seen whether it will be accepted a a bug now that the report is there.

---

As far as I can see it's neither accepted nor rejected and probably never will be. Just like SVC-7552, it's permanently stuck at the bottom of LL's to-do list.

I spent two weeks trying to teach the Linden assigned to the cause the basics of mesh physics, then he simply stopped responding. Later I mentioned it to Drongle and thanks to his vast knowledge of everything mesh, we were able to pin down and document exactly what happened. Still no response.

I just posted a new JIRA about it (BUG-8166). This time it's a feature request, asking them to provide proper documentation and such about mesh physics. That's the least they can do.

[Aquila Kytori]

 

(yes, agreed still images are better that .gifs so will be returning ot them in future posts )