Thursday, June 26, 2014

Freeing up the Prims

Unless you've been hiding under a rock (which I pretty much have been), you know the Lindens no longer calculate a region's capacity for objects based upon the number of prims. Instead, they use something called land impact.

Land Impact is calculated by use of an algorithm, which is a Greek word meaning the Lindens have made up a new scheme for land use out of whole cloth.

Prims, whether regular or sculpted, still count for one, if the Physics Shape Type (you'll find it in the Features tab of the Edit menu) is set to Prim. Mesh, however, affects the land based upon the already mentioned algorithm. Thus, one mesh object may and usually will consume more than one unit of land impact. How many depends upon number of vertices, size, physics shape, and level of detail. To see those numbers when editing an object, click More Info just below the Land Impact number.

Here's a page about calculating land impact, and here's a longer explanation.

Because of the large amount of prim-based content, the Lindens have retained simple prim count-- one prim counts as one prim-- in addition to a parallel way of counting for mesh. Linksets can be switched from one to another Physics Shape Type in the Features tab of Edit. There are three choices: Prim, Convex Hull, and None. I'm not sure about the last; whenever I select it it tells me the root prim can't be set to none,

The happy thing I learned from reading about land impact is it's possible to reduce land impact for some prim linksets by changing the Physics shape from Prim to Convex Hull. There are some caveats, the primary one being mesh and sculpts can't be part of the linkset. Prims with high render cost-- torii, for example, can count for more than one when set to Convex Hull-- but simple prims like cubes, when linked, can count for less than one land impact unit per prim. In fact, they can ring in at only 50%. That means a linked set of 100 cubes will count only 50 for land impact!

Rounding is always up, which means a three-prim Lilith Heart plant will count as two in land impact when set to Convex Hull-- but two linked three-prim Lilith Heart plants will reduce to just four prims. A 30-prim house might ring in at 17; the amount of reduction depends upon the complexity of the shape. In some cases there might not be a reduction, and in some cases, the land impact might be greater.

Hollowed prims act as if they were solid when they're set to Convex Hull. That means you can't pass into a house if the doorway is a hollowed prim. However, if offending prims are removed from the linkset and set to Prim physics shape, the remainder of the linkset can be set to Convex Hull, leading to a reduction in land impact.

This was big news to me and great for Whimsy. I spent a couple of days changing the physics shape of linksets from Prim to Convex Hull. In some cases I found myself unable to pass through space which I had always been able to walk through because I hadn't noticed a hollow prim. When that happened I just changed the linkset back to the Prim shape; in a few cases, I made a separate linkset from the hollow prims and set the remainder of the linkset to Convex Hull.

When I was finished I had free up more than 700 prims on our homestead Whimsy Kaboom, and more than 2000 on Whimsy!

Bam! My torii gate went from 20 LI to 10! Bob the giant drinking bird went to only 16. The little tiki house Melissa Yeuxdoux lives in went from 43 to 22!

When the issue of the out of control PG Den of Iniquity is settled, we will have more than 4000 prims free on Whimsy.

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