Rendering optimal solar shadows with plural sunlight depth buffers

We propose a novel method, based on the two-pass Z-buffer algorithm, to cal culate shadows with sufficient precision and efficiency for rendering a day time landscape with solar penumbrae. The special feature of the proposed me thod 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 tim e and quality of shadows.