[sldev] Sculpties: Vacuum-Forming, Skittering, Zone Linking

[Philip Rosedale]

Hi Dale,

Some history, perhaps helpful... Sculpties (though not with the same 
name) were actually a broad idea we had first talked about way back at 
the beginning of LL - around 2001.  I was personally really interested 
in using wavelet compression (which is the kernel in JPEG2000) to 
compress fixed topologies (prims) as a way of creating arbitrary shapes 
that could be streamed to the viewer at a speed adequate to allow 
'flyover' of typical terrain/objects without falling behind.  While it 
is true that using lossy compression against fixed vertices results in a 
object type with weaknesses when compared to full mesh descriptions, the 
difference in terms of compression is really enormous.  Though I am not 
versed in the most recent forms of lossless arbitrary mesh compression, 
they are generally nowhere near the 10-100x compression that can easily 
be obtained with the lossy compressor/sculpties.  BTW, we didn't do 
sculpties back in 2001 because it was lots of work and the additional 
CPU load for decode seemed like a bad idea for machines at the time.  A 
great new developer (Karl) joined us recently and independently 
implemented something pretty identical and so we got the capability out 
there.

I would consider full mesh compression to be an idea for the future, and 
as you say one would need to carefully restrict use so as not to have 
the full mesh prims badly slow the loading of other objects.

Also, I think we need to work most on dramatically increasing the load 
time of scenes, which would make this disparity in download times all 
the more jarring.  We have some ideas about how to greatly speed the 
loading of objects so that those 'flyovers' we dreamed about back then 
actually work with the current density of objects and textures in SL.

Philip