Very strange collision behavior on clutter item

[syscrusher]

I'm working on an update to my Inkle Loom clutter items. The update provides a couple more variants of the object, but mainly is supposed to improve the collision mesh. The originals work correctly in CS and in game, but I discovered that I had accidentally made them simple box collisions, and that the box is slightly offset below the visual base of the object, making it annoyingly float off of tables and such.

I have tried everything I can think of to get any of several custom collision meshes to work correctly. They look fine in NIFskope, they work perfectly with the "F" key and with the Havok simulator in the CS. In the game, the blasted things will sit just fine on furniture but, but if dropped they squirm around as they slowly sink through the floor! I can replicate this problem in both my own house interior and in vanilla building interiors, so I have ruled out my house mesh as the cause. Oddly, the problem doesn't seem to replicate if I drop one of the items on the ground outdoors.

The meshes I've tried include:

* Simple box mesh (works).

* Several of my custom collision meshes (one at a time) with the "draw type" set to "box" rather than "polyhedr" in Blender (accidentally) (works).

* Convex hull mesh as a starting point, deliberately low-poly-count settings, then hand-tweaked to make its vertices correct locations.

* Hand-created from-scratch polyhedr collision mesh.

* I also tried assigning a material property to the mesh, reusing one from the rest of the model (in this case, the vanilla UC furniture wood material).

The last two exhibit the problem.

My settings on the meshes that fail, in Blender, are:

* Draw type "bounds". Draw extra "wire", boundary display "polyhedr".

* Exporting settings start with Oblivion defaults, then choose "clutter", then choose "wood".

* Exporting with mass of 3 units.

I've also been looking at a couple of vanilla clutter items, and the only real difference I'm seeing with my mesh and theirs is that mine lacked a NiStringExtraData node that contained the parameters for mass, elasticity, and such. I copied that branch from a vanilla item into my NIF, but it didn't help.

Now, here's where it gets weird: I have been assuming all along that this is happening because I don't know much about creating Havok items in Blender. This is my first Blender project that is not static (my statics pretty much work fine, so I thought I was ready for the next step). But....I can replicate this problem with one of Meo's globes that I have not modified in any way! Now, first of all, Meo is a bona fide expert, unlike me. And furthermore, Meo does not use Blender (uses 3DS instead). And it's not a generalized problem with my game environment, because I tried a bunch of vanilla clutter such as crystal balls, Welkynd stones, and soul gems, and cannot replicate the problem with any of them.

I've tried everything I can think of, have walked through several of the collisioning tutorials step-by-step, and just can't seem to see what I'm doing wrong.

I'm sure I'm not the first to encounter this -- anyone have any ideas, or willing to take a look at my NIF and Blend files? I would prefer someone to help me know what the problem is so I can fix it, rather than just fixing my mesh, because I need to understand what went wrong so I'll do it right next time.

Thanks!

Syscrusher

[syscrusher]

By the way, with my convex polygon mesh, I specifically checked to make sure that the mesh is truly geometrically convex and doesn't have any holes.

[Artisanix]

Try to run convex hull script on object and do not touch this shape manually later, and do not change it to polyheder type (just leave that field blank), and export such collision instead and see whether it works.

[syscrusher]

Try to run convex hull script on object and do not touch this shape manually later, and do not change it to polyheder type (just leave that field blank), and export such collision instead and see whether it works.

Will do, and will report back. I'll have to run the convex hull script at greater precision this way, because at low-poly settings it doesn't do a very good job on this particular model. But for a test that should still be okay.

[syscrusher]

Could you hear the cheering from your office?

Test results in detail:

* Deleted my polyhedr collision mesh, and recreated from scratch using convex hull script. (Sidenote: You were right the other day; that script is not exactly brilliant about some of its decisions.) Left the result absolutely untouched, even though it didn't match my geometry quite right. Tested in game. SUCCESS.

* Back in Blender, moved vertices on the above collision mesh to more closely match my geometry. Exported with same settings into NIF then tested in game. SUCCESS.

It sits correctly on the furniture, and it collides perfectly with floors, light fixtures, NPCs, and everything else I threw it at. (My lovely wife, who is an inkle weaver, said she is no longer willing to weave on the test loom I threw down the stairs and off of a couple of balconies...)

Both of the above cases work correctly in the CS with the F key and with Havok simulation.

So, clearly, this has fixed the problem, for which I offer much thanks and a . Now I know that clutter items cannot be polyhedr boundary display, or at least not the way I was doing it. Suppose I needed to create a from-scratch collision, for really good optimization, or I had a very simple visual mesh and wanted simply to clone it to become its own collision geometry. Is there a way in Blender to completely unset the boundary display? Or is it simply a matter of using the convex hull as a starting point and being very careful to never select from that dropdown, ever?

Thanks again for your suggestion -- that seems to have fixed the problem!

[syscrusher]

Just wanted to say thanks again for the quick help, Trollf. My updated resource is RELz a little while ago, and you are mentioned in the credits for this version.