Prims (Content Creation)

From Open Metaverse Wiki

Opensimulator: Content Creators: Models: Prims

Prims are procedural meshes, that is they are generated by the viewer from a (fairly simple) mathematical formula. The main advantage of this compared to polylist meshes is that a prim has much lower streaming cost. All the prim shapes currently supported are created from a set of only 15 parameters so the amount of data needed for even the most complex prim shape is only a fraction of what is required for transferring even the simplest (polylist) mesh. Prims also seem to be easier for most people to build with and they have turned out to have considerably lower effective render cost than similar shapes made from mesh (although this may be because the rendering pipeline was optimized for prims right from the start).

Faces

Depending on the shape a prim can have anything from one to nine faces.

Level of Detail

Unlike meshes and sculpts it is fairly easy for a computer to generate simplified LOD models for prims so this is usually not something the content creator has to worry about.

Physics

The physics of prims matches the visual model exactly. Hull physics are used whenever possible, triangle physics when no hull class matches the shape.

Most prim shapes have physics simple enough they shouldn't cause any significant load on the physics engines. There are some excepions though and it's always a good idea to set any objects that don't actually need physics to phantom or physics shape none and any objects that only needs a simple collision body to convex hull.

Exporting and Importing Prim Builds

Two of the most common viewers for OpenSim, Firestorm and Singularity, both have functions for exporting and importing single prims and linksets made from prims. Singularity uses an XML format which is also supported by some older viewers. Firestorm has its own oxp file format.

Prim builds can also be included in OAR and IAR files and be exported and imported that way.

Links

Documentation

How SL Primitives [Really] Work

Link to the WayBack Machine since the blog the article was originally posted on is long gone.

Avi Bar-Zeev was the inventor of the prim system that was adopted by Second Life in 2002 and later by opensim. In 2008 he started documenting his work. He never finished but what he did publish still contains a lot of valuable information.

Guides

Lag: Geometry (prims, meshes and sculpts)

A short article on the differences in lag caused by prims, meshes and sculpts.

Tutorials

The ultimate guide to prim twisting

Not exactly what the title claims but still a very good resource to learn some of the most common shapes that can be made from prims.

Prim twists

A few shapes not included in the ultimate guide.

Content Libraries

Online repositories for prim builds. Mostly as parts of OAR or IAR files but also some in Singularity's XML format.

Please note that all the content from these sites has already been uploaded several times to the hypergrid and it is recommended to use existing uploads whenever possible. There's no need to load the grid servers with more duplicates than necessary.

Ener Hax

  • Link: http://enerhax.com/ (confirmed 2023-05-29)
  • Content: All kinds
  • License: Various Creative Commons licenses - see individual items

Objects in XML format and complete OAR files.

Oligo Academy

  • Link: http://oligo.academy/my/ (confirmed 2023-05-29)
  • Content: All kinds
  • License:
    • Content from Zadaroo: CC0
    • Content from miltaryverse.org: CC BY-SA 4.0

OAR files from the now defunct militaryverse.org site and also an alternative source for Linda Kellie's OAR and IAR files.

OpenSim Archive

IAR/OARs, items, objects scripts and regular builds of OpenSim.

Outworldz

Collection of textures, meshes, objects, avatars and other items.

Zadaroo

Zadaroo is perhaps best known for hosting all of Linda Kellie's works after Kellie took down her own website but there is also some good classic content by the siteowner there.

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