I have an unusual request. I'm updating an isometric 2D game with a 3D engine (Sauerbraten), but keeping the game 2D for now (using orthographic projection), a decision which I don't intend to debate in this thread. There are a lot of existing sprites which the update will continue to use. However, the engine renders models, not sprites. To render the sprites, I would like to be able to convert them to animated models. These models would obviously be just flat quads. They would need to be in a standard animated format that is easily converted to most other formats. I was thinking there might be some way to use skeletal animation to achieve the effect of sprite animation using flipping and folding of polygons so that at any one time only one quad is visible. Is there any tool out there that will perform such a conversion, or is this requirement just so unusual that I would have to do this by hand, thereby making it more time-effective to attempt to hack sprite rendering into the engine's pipeline?

Thanks b3rs3rk. I searched the engine source for billboard and found some comment indicating that explosions use billboards. So now I have something to investigate that may lead to a solution.