Soft Shadows with Soft Objects : a proof of concept

We propose a method to generate penumbrae (half shadows) in scenes that are composed of simple 3-D geometric primitives. Penumbrae occur when objects are illuminated by a light source with nite extent. Traditional methods to generate penumbrae are based either on extensive geometric reasoning or on signal processing (sampling and smoothing). In either way they have a high computational complexity. We propose a third alternative that is based on function evaluation, not unlike the way in which implicit surfaces are de ned by means of evaluating suitable eld functions. Our method starts from a physically correct model for the shape of penumbrae, and proposes some ways to compose the penumbrae for individual geometric primitives. We discuss the e ciency issues related to our method, and we indicate some restrictions for its application.