I don't believe that this is changeable at the moment - there are too many things hardcoded into the Linden Labs viewer. Hardcoding around 256 has probably also built up within OpenSim itself, so this would have to be resolved too.
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The 256 x 256 limit
Fri, 01/09/2009 - 21:24 — Justin Clark-Casey (not verified)I don't believe that this is changeable at the moment - there are too many things hardcoded into the Linden Labs viewer. Hardcoding around 256 has probably also built up within OpenSim itself, so this would have to be resolved too.