Texture loading , some thoughts

Here's my two cents:

How about loading them beforehand but keeping them compressed in the RAM? When you would like to use them, you can just decompress them and bind. Then free the decompressed memory when you're done.

One thing you can do to reduce the memory overhead is to load all the textures, but only load the bottom few mipmaps of each of them. This is a big saving because the top mipmap level accounts for 75% of the data in a texture.

During gameplay you then load the more detailed textures for things that need them on another thread, and use them in place of the low detail ones when they are available. Ideally you would also look ahead a bit, and load what you will need 'soon' as well so the player doesn't see the switchover. Don't forget to unload the big textures that the player can no longer see as well.

However, before you go to all that trouble make sure you compress your textures with DXT1 (or DXT5 if they have an alpha channel). That will cut them down to 1/8th (1/4 for DXT5) of the uncompressed size. It will also make the game run quicker as it saves on memory bandwidth on the graphics card.

I'd suggest loading them all at once. You'd be surprised how many textures you can load for very little RAM. If you creating a level-based game there is virtually no reason not to have all textures loaded at once. Not to mention, RAM is cheap these days. Every decent PC has 1 Gig at least, 2 Gigs preferably if they have Vista, since Vista itself consumes a Gig. =(

Unless of course you are coding a "seamless world" engine. In that case, good luck. It is very hard to do. =)

Thank you all... It gave me some direction to look.