Texturing Best Practices

I'm starting a thread on Best Practices in the realm of Texturing, since I can't seem to find its equivalent anywhere else.

I'd start with some questions:

Does anyone know how textures are loaded into SL?

Specifically:

does loading an alpha-channel for transparencies slow things down? what's the slowage difference between 100% clear, vs., translucent?

what about creating a "texture sheet" as in this example here -- does each piece that uses the same sheet has to load up the whole same sheet, or is only part of the texture zone loaded?

what about using alpha-channels in a "texture sheet" as above; what are the performance issues, then?

The files that contain an alpha channel are slightly bigger, since it contains now the 3 RGB channels plus 1 transparency information. But its not much of an issue, since when you actually need transparent textures, there is not much choice.

There is no difference in size between clear and translucent. Its just a variable like colour. Red doesn't take up more space than blue, right?

However, since it goes through some sort of jpg compression, the complexity of the transparency information matters more than the actual intensity of the alpha channel. Complexity meaning, if the alpha channel looks contains mostly large swathes of more of the same, it compresses more.

But when it gets loaded on your graphics card, it occupies the same amount of memory.



When a texture is accessed, it needs to be translated into an OpenGL format before your graphics card can display it on your screen. The whole texture sheet will have to be loaded into memory before the GPU can display it for you. So basically, it makes no difference if you use part or whole of the texture.



Same thing. Just more RAM needed. You'll only notice much of a difference when you run out of video RAM. For those with 256Mb or 512Mb cards, this seldom happens. More likely, you'll get bored of the place first before you finish loading up all the textures needed to fill 256Mb worth.

One little thing missed out there... sometimes you see apparently solid textures that give alpha-sort problems. I guess if it's one one element on a sheet that uses the alpha's for everything else I'd go for it too. If it's the whole texture and you're saving it at 32-bit you're wasting memory in the graphics card and you're giving yourself fun and games with building in world unnecessarily.