Wednesday, February 6, 2013

Why Are My Builds Using So Many Prims!

If you have built something in Second Life with, say, ten prims in the linked object (i.e. LINK_SET) and you have then seen that the land properties for the sim suddenly jump to show you're using, say, three hundred then you have discovered the problem that has been perplexing me for some days.  For an exhaustive and excellent discussion on this matter, read Prims, Prim Equivalent, Land Impact... a too-long guide by Jenni Darkwatch.  If you are seeing the problem I have described then read her article as my purpose is to write a summary of how it applies to my situation rather than to repeat her work.

The answer to the problem is that some prims, for example a torus, are very expensive in terms of sim overhead while a prim such as a simple box is not.  To reduce the overhead in defining the physics of such prims you can go to the Features tab within Edit to see a PRIM PHYSICS pulldown menu that lets you set any individual prim in your build to PRIM, NONE, or CONVEX HULL.

PRIM is what you have always known when you have edited but today there may be more land impact from that prim than you realise.  In other words, it may appear to you as one prim but for for land impact it may be accounted at many more than that.

NONE is functionally the same as setting the prim to PHANTOM except the rest of the object will not turn Phantom when you link it.  The additional benefit is that setting the prim to NONE means it is removed from land accounting.  Note that it still counts as a prim but its land impact is eliminated and this is the crucial point.  For an object such as a torus the land impact can be huge.

CONVEX HULL is used to define mesh prims but that discussion goes beyond the scope of my purpose and you will need to read Jenni's article to understand how this setting applies to you.

The consequence to using NONE for the prims in your build is there is no longer a collision detected by the physics engine which means you can walk through doors, walls, etc.  If you care about that then it's not a big concern as setting those prims back to PRIM is not expensive, they are usually made from box prims and therefore do not have much land impact.

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