1. A method that in use is performed by a computer animation and graphics generation system of the type including a processor, a 3D graphics processor coupled to said processor, and a memory coupled to at least the processor, said 3D graphics processor projecting 3D values onto a 2D viewing plane for display, said method for animating plural 3D moving objects and comprising: determining whether said plural 3D moving objects overlap in 3D space; if said plural 3D moving objects overlap, substituting use of at least one 2D imposter model common to said overlapping plural 3D moving objects in place of respective 3D models of said plural 3D objects; processing said 2D imposter model within a 3D world; and generating an image of said plural moving objects moving one object in front of another based on said 2D imposter model for display at least in part in response to said processing.