Rendering optimal solar shadows using 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 feature of the proposed method is that the precision of the shadows can be preserved to be superior than that of any visible surface by using the appropriate number of plural shadow buffers; it gives a fairly satisfactory trade-off between computation time and quality of shadows. By using the shadow buffers, before calculating solar illuminance we can divide visible surfaces into three types of fragments, that is, bright regions, umbra regions, and the remaining penumbra regions. Thus, we can efficiently render a daytime landscape with sufficient precision of penumbrae because the algorithm can set the calculation points of solar illuminance variably, with their number depending on the type of region they belong to