[sldev] Reformatting Textures for the cache

Dzonatas dzonatas at dzonux.net
Thu Mar 22 20:36:43 PDT 2007

John Hurliman wrote:
> For the record I think some variation of a direct filesystem cache 
> will probably yield the best results, but I wanted to pitch in that a 
> lot of the overhead with using a filesystem is more than just finding 
> the file. The OS has to check if you have permission to access that 
> file, check if any other programs have an access lock on that file, 
> and do some bookkeeping work when you open and close the file. Working 
> with a single large file containing lots of data (like a VFS) can be 
> as simple as a malloc() and copying data in to memory.
mmap() and gnu malloc() that has been redirected to the mmap() segment.

I have other ideas to do a pretty fast cache, but it would not be easily 
portable. I've implemented it for another system a few years ago. We'll 
see if it is practical for this, and then I'll release more detail.

> To further the discussion about using the uncompressed filesize, there 
> are quite a bit of different potential dimensions of images in SL. the 
> valid dimensions that I am aware of are any combination of 8, 16, 32, 
> 64, 128, 256, 512, 1024, and 2048 (ridiculously huge for a real-time 
> 3D world). The valid number of layers are 1 (grayscale), 2 (grayscale 
> + alpha), 3 (rgb), 4 (rgba), and 5 (rgba + bump, used for avatar 
> bakes). It's been a while since I took statistics, but that's quite a 
> few different possible sizes of uncompressed image data. An avatar 
> bake texture is 512x512x5 (except for the eyes), 1.3MB and there are 
> three (or four if they have a skirt) of those for every avatar you 
> see. Reading almost 6MB from the disk for every avatar you encounter 
> seems like it would get out of control quickly. I can provide some 
> sample SL texture data in compressed JP2 and uncompressed TGA format 
> if people want to benchmark various compressors against it, let me know.
That is nice except SL has taken a step away from those formats and one 
into "materials." Those formats I'm sure will be still supported, but 
the cache cannot be just optimized only for those formats.

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