Rendering optimal solar shadows with plural sunlight depth buffers

We propose a novel method, based on the two-pass Z-buffer algorithm, to calculate shadows with sufficient precision and efficiency for rendering a daytime landscape with solar penumbrae. The special feature of the proposed method is that the shadows can be preserved with a precision superior to that of any visible surface. We use the optimal number of plural shadow buffers to do this; it gives a fairly satisfying trade–off between computation time and quality of shadows.