Mega Prim

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A mega prim (also referred to as megaprim, mega-prim or huge prim) is a primitive with at least one side being greater than 10m. Their creation is not possible due to limitations.

History

In 2006, Resident Gene Replacement managed to tweak the viewer in a way that allowed him to create these objects despite their limitations, until Linden Lab fixed the security hole some time later. The mega prims were distributed and spread quickly across the grid, since Residents found many ways to use them in their builds. While Linden Lab didn't ban the objects completely, their policy was to return them if they were a "nuisance". In a Town Hall discussion at December 20th 2006, Linden Lab announced that they were going to allow the use of mega prims on private estates^[1]. After open sourcing the viewer, another bug exploit allowed the creation of mega prims for a limited time. Residents took the chance to create a variety of these objects in many different sizes, even those which covered multiple regions completely. Linden Lab announced and discussed plans on using methods to prohibit the use of mega prims greater than 256m in one dimension, but then decided to only limit them to 64,000m (64km), since they found legitimate use for them (for example in horizons and skies).^[2]

Mega Prim Pros and Cons

Prim density and lag

Using a mega prim instead of multiple regular prims (for a wall, a floor, etc), decreases the number of faces which need to be drawn by the viewer (or, depending on how "smart" is your graphic driver, the number of occlusions to calculate so to avoid drawing hidden faces) can be reduced dramatically. ^[3]

Draw distance and rendering

Very large mega prims will not be rendered at all sometimes by the Viewer. The only approach to fix this would be to increase draw distance, therefore increasing lag.

Land controls and parcel limits

Some problems with mega prims are obviously related to their huge size. They can reach far beyond parcel borders and disturb neighbors with their presence. Residents might not even recognize that it is a mega prim which is hindering them, since they might be inside the mega prim and therefor won't be able to see it.

Outdated Mega Prim Issues

Previously (prior to Havok 4) it was reported that the graphics engine wouldn't be able to work well with prims larger than 256 meter in any dimension.^[4]

Unsupported claims follow, see talk page It has been recently proven and tested that mega prims, in certain situations can be a large cause of sim performance, creating lag. It was hard to prove because the specific situations that megaprims cause problems is when avatars or objects are colliding with or standing on (also a collision) a megaprim. The amount of lag a megaprim will cause can also depend on its size. The larger a side that is being collided with, the higher the collision cost on the region appears to be. That being said, just one avatar and a few objects colliding with one megaprim on a quiet region will not cause much noticable problems. When combined with several megaprims floors in public busy places, the amount of sim degradation is extremely noticable. Estate owners and managers can monitor region collision debug screens to see the collision cost of megaprims are.

Building with Mega Prims

Mega prims can be edited like any other prim despite that it's not possible to edit their dimensions. The attempt to edit the dimension of a mega prim will result in all sides of the mega prim which are greater than 10m instantly switching back to the regular 10m limit. To be able to edit and move some huge mega prims, it is suggested to access the advanced menu (press Ctrl-Alt-⇧ Shift-D) and to toggle "Limit Select Distance" off, as well as "Disable Camera Constraints" on.

In order to support builders who'd like to use mega prims, many Residents made them and are providing them for free. You can find many mega prim packages inworld or at SL webstores.

Future of Mega Prims

While Linden Lab is still not supporting or endorsing the use of mega prims, developer Andrew Linden talked about^[5] future plans on what he called the "liberation" of mega prims. He is planning to

1. Allow parcel owners/managers to move (or maybe just return) objects that overlap their parcels.
2. Provide UI feedback to the Resident when moving their objects, indicating whether they overlap neighboring parcels.
3. Maybe provide real-time enforcement of parcel permissions. That is, allow parcel owners to set a paranoid bit “I don’t want anyone, or these specific people, from putting stuff on my parcel”

He noted that "once that is done then perhaps we will allow you to make prims/objects as large as you want as long as they fit on your parcel."

References

1. ^ Linden Lab allows use of mega prims on private estates (see at [14:55])
2. ^ Linden Lab doesn't ban 256m mega prims.
3. ^ Comment on VWR-1048: Raise sim prim limit of 15.000 to more.
4. ^ The big prim problem - Bugs with mega prims
5. ^ Read the 2008-04-09 and 2007-12-21 transcripts of Andrew Lindens Q&A sessions about the havok4 engine