Replicated textures

[Roger H. <rog...@mi...>]

I have been thinking about a problem we are having with multiple
objects having the same texture on them. They are gobbling up
all the logical address space and also causing thrashing on
Macs with less than 2GB of RAM.

At one time, when we read in objects, we would compare all
their textures with all existing textures and all their own other
textures. We would then make identical ones share the same
texture shader objects. This worked fine except we had to take
it out because users were complaining about the speed of
reading files.

The comparisons had the obvious speed ups of comparing
the size etc first before comparing the actual pixels. What I
am now thinking about is storing a hash of the pixels so
that most of the time I will only have to compare the hash.
When two identical hashes are found, I do not mind doing
the comparison because the chances are very good that
the textures really are the same and I will be saving memory.

The question is where to store the hashes. I could put them
in a custom attribute. This would be fine for me, but would
we be missing an opportunity. If they were stored in the
texture shaders or even the storage objects, would this
be of any use to either the renderers or the saving code
or anywhere else?

Roger Holmes.