Rendering of shadows with hand-painted appearance

Shadows are rendered automatically with a hand-painted appearance. The shadow region is divided into a core and a penumbra. A core perturbation zone is defined between the core and penumbra and a penumbra perturbation zone is defined between the penumbra and an unshadowed region. Within each perturbation zone, a texture is applied to each pixel to map the pixel as being inside or outside the core or penumbra boundary, thereby defining a displaced core boundary and a displaced penumbra boundary. The displaced boundaries can be non-linear and discontinuous. When shadows are rendered using the displaced boundaries, a hand-painted appearance can result. An additional texture can be applied in the penumbra to further enhance the painted appearance.