Basic Physics Shape Questions

[Pamela Galli]

Well I made a physics shape for my door and all went well so now am considering making them for the walls.

 

So I made planes that fit in the walls but then realized I would need more than 8 materials so I would have to break it up.  Then I start wondering, do I upload the house in pieces to match the physics shapes?  I can't upload a physics shape separately and stick it in the walls of the house like I would SL prims, can I?

So not sure what to do -- if the LI cost is not too high I might just use regular prims.

 

[Maeve Balfour]

Pamela: I am assuming that are you talking about breaking up your actual HOUSE INTERIOR WALLS into segments due to material shortages.

If so, just simply reshape your physics hull mesh to suit each individual segment. If the walls themselves are very basic plane meshes, you could even use those as the basis of your physics - personally, I would remove any tiny surface areas and leave it as purely large surfaces only (areas smaller than an AV can fit through, I would remove entirely). Doesn't have to be all joined up either (at least from my own experience with physics), and it doesn't need to look pretty at all LOL, just functional.
If the physics mesh only consists of flat planes (as per your walls), just ensure all the normals are pointing in the desired direction of interaction - if you are duplicating and disassembling an original wall for this, the normals should already be facing in the correct direction.

The MAIN consideration is that your bounding box volume matches that of the target mesh wall segment (so that they match up correctly).

If your physics mesh hull is already optimised as such, you simply point the uploader to it in the physics section - no analysis is needed.

Piece of cake overall though, especially once you have done it a couple of times. If you ensure your triangles in the physics have all the tiny triangles removed, the physics shouldn't have an bearing on your final LI count - the display cost etc will be higher. Definitely better than using separate shapes for the physics (less hassles) - trust me, I explored that route a while back, and doesn't save prim count at all (just matches it if anything). Less pieces for customers to lose too if they are pulling things apart! (You CAN use the physics mesh hull as a separate object inworld to achieve the physics (via invisibility) in a worst case scenario, but I don't recommend it for these reasons).

So yah, physics mesh hull WITH the main mesh component object is the best way to go, I think.

:matte-motes-smile:

[Drongle McMahon]

If you use invisible prim boxes linked to the walls for the physics shape, and set the wall mesh physics shape type to "none", the physics cost will be only 0.1 for each prim box. To get this low cost, they must have no distortions other than stretching along the main axes. (As long as that is the case, they can be treated as Havok primitives, which are the most efficient shapes.) This is probably the way to get the lowest physics weight. It has the slight disadvantage that, if it is mod, they user can accidentally unlink them, which could cause problems.

The same boxes uploaded with the mesh as a decomposed physics shape will cost 0.36 physics weight each. I have usually found I can get a wall physics cost lower than the download cost using a physics shape in the upload, either with boxes like that or using simple triangle-based (no "Analyze") shapes with no edges so that there are no small triangles. As long as it's lower than the download cost, it doesn't affect the land impact.

ETA - Yes, Maeve is right ... for walls, the triangle-based shape with small triangles removed, is usually cheaper than the decompsed shape.

[Pamela Galli]

Thanks Maeve and Drongle -- really appreciate it!

[Senkiya Zsun]

---

Pamela Galli wrote:

Well I made a physics shape for my door and all went well so now am considering making them for the walls.

 

I can't upload a physics shape separately and stick it in the walls of the house like I would SL prims, can I?

---

Of course you can. Just make a very simple, solid mesh with the same overall dimensions as your wall, add your physics shape with all the holes in, then make it invisible. Have I misunderstood something?

 

ETA: sorry just noticed Maeve says the same thing at the end of her reply.