[Algorithms] Skeletal Character Animation with Mesh Interplation?

[Bass, G. T. <gt...@ut...>]

List folks,

	I know two common forms of character mesh animation are quake-style
mesh interpolation in which each animation keyframe is stored as a complete
set of vertices, and half-life-style skeletal animation in which only the
bone transforms are stored per keyframe.  I'm guessing most skeletal systems
interpolate a skeletal pose from the nearest two keyframes every time an
animation frame is rendered, but I'm curious if there may be a cheaper
alternative that combines the best features of both methods.  I'm not sure
if the following is a widely used technique, but it just occurred to me, so
I thought I'd suggest it to the list.

	Consider this: every few frames, perhaps every 1/10 second, the
skeletal system is used to create a complete target mesh for the next
skeletal keyframe, then as each frame is rendered the output mesh is
interpolated nearer the keyframe mesh until they are the same, then a new
target mesh is created for the next skeletal keyframe.  This would double
the storage needed for each output mesh as compared to a pure skeletal
approach, but the per-frame computations could be far less, and there
wouldn't be nearly the kind of memory demand one sees with pure mesh
interpolation.

	Obviously there are some downsides to this.  If you only generate
target meshes once per keyframe, then you can only mix multiple skeletal
animations on exact keyframe boundaries, although some skeletal solutions
may already have this limitation.  Obviously the system becomes less
efficient if you need to switch animation sets between keyframes, though
perhaps still more efficient than pure skeletal animation except in the
unlikely worst case scenario in which the animation set changes every single
frame.

	Anyway, I thought this idea may help reduce CPU usage when
simulating environments with large numbers of skeletal system characters.
As usual the price of reduced CPU usage is more memory usage.  Any comments
on this?  Is anyone already doing this?

Regards,
Garett Bass
gt...@ut...