Skinning Cubic Bezier Splines and Catmull-Clark Subdivision Surfaces

Smooth space deformation has become a vital tool for the animation and design of 2D and 3D shapes. Linear methods, under the umbrella term of "linear blend skinning", are the de facto standard for 3D animations. Unfortunately such approaches do not trivially extend to deforming vector graphics, such as the cubic Bezier splines prevalent in 2D or subdivision surfaces in 3D. We propose a variational approach to reposition the control points of cubic Bezier splines and Catmull-Clark subdivision surfaces-or any linear subdivision curves or surfaces-to produce curves or surfaces which match a linear blend skinning deformation as closely as possible. Exploiting the linearity of linear blend skinning, we show how this optimization collapses neatly into the repeated multiplication of a matrix per handle. We support C-0; C-1; G(1), and fixed-angle continuity constraints between adjacent Bezier curves in a spline. Complexity scales linearly with respect to the number of input curves and run-time performance is fast enough for real-time editing and animation of high-resolution shapes.