http://bugs.winehq.org/show_bug.cgi?id=18227
--- Comment #1 from Tobias Jakobi liquid.acid@gmx.net 2009-04-26 11:42:22 --- MSDN entry about vertex tweening: http://msdn.microsoft.com/en-us/library/bb206340%28VS.85%29.aspx
This looks surprisingly easy! Looks just like ordinary linear interpolation of vertex position and normal - I though "tweening" to be a bit more sophisticated...