You’re going to have to draw the background again. The only real question is whether or not you have to draw it made from its individual elements.
On the assumption that your background is a tilemap (I’ll get into this asthetic issue in a moment), you have two options to speed up how fast it draws. You can render the tilemap, from the separate tiles, to a texture directly, using ARB_render_texture. Or, you can use glCopyTexSubImage to copy the framebuffer (containing just the tilemap background) to a texture. In both cases, you will need to render the texture to the framebuffer again, but you won’t need to do all of the texture swapping and so forth that rendering it from the tilemap will do.
BTW, unless your tilemaps are rather small (say, 32x32 tiles with a map being no larger than 128 tiles on any axis), this isn’t going to work very well. Mainly, because even a GeForce 4 can only have 4096x4096 textures, and 32*128=4096. So, you will not be able to render the entire tilemap into a buffer at once. Not only that, even if you did, you’d be taking up enormous ammounts of memory to do so.
In any case, a tilemap is not very complicated. I would guess, on modern cards (GeForce or better), you should be able to get at least 10 layers at 800x600 using 32x32 sprites drawn in OpenGL with quads. GL rendering is probably not going to be your performance bottleneck.
As such, my personal suggestion is to not bother. Just using OpenGL at all will give you plenty of performance, given the requirements of the game and so forth.
On an asthetic point: how can you possibly get away with this? Do none of your tilemaps support multiple layers where sprites can be in front of one layer while behind another (allowing sprites to be hidden by a tilemap)? Even if you don’t have layers in front of sprites, you can’t use paralax scrolling if you want to try this rendering method.
BTW, I hope, for your sake, you get more programmers on the project. An entire RPG is not a simple or trivial undertaking, even with the best design in the world.
Also, the game uses a VERY efficient engine I created that allows you to just put the data in to a matrix (can’t say too much, or I’d be leaking too much)
Sorry; doesn’t impress me. Of course, since you didn’t say anything about what the “data” in question might be (graphics, sound, plot, etc?) or what this “engine” does (graphics, sound, plot, etc?), how could it? I have no idea what you are referring to.
if you have an answer to this, please email me at firstname.lastname@example.org
Sorry, this is a public forum. If you want answers, you’ll have to come back to see them.