[sldev] Texture caching

[Jason Giglio]

Alex Suter wrote:
> 
> Usually because of disk space issues, in that you can rapidly fill it 
> all up.
> 
> Could be a slick alternative implementation... trade disk space for speed.
> 

It doesn't have to be an alternative.

We can have a three level cache, each level maintaining its own 
replacement list, discard policy, and size.

Memory
Uncompressed Disk
Compressed Disk
Network

A request would filter down through them.

-Jason