Extended shadow maps

The most popular methods for interactive hard shadows rendering are shadow volumes and shadow maps. Shadow volumes generate precise shadows but require high fill rate. Due to excessive fill rate requirements, shadow maps are probably the most widely used means for generation of shadows, despite their well known aliasing problems. In this paper, Extended Shadow Maps are introduced, as a means to reduce required shadow map resolution and enhancing visual quality of shadows by encoding additional information about silhouette edges into the shadow map by drawing quads for silhouette preservation. Recent algorithms using this technique were not suitable for computer games due to their hardware requirements, because in this types of applications, high frame rate is required. Our algorithm, Extended Shadow Maps creates anti-aliased shadows using fast fixed-point pixel shaders version 1.4. For shadowing detection only 4 arithmetic instruction slots and 3 texture pipes are used. Also, all geometry required to render anti-aliased hard shadows using our new method can be stored in static vertex and index buffers on graphics accelerator. Additionally, using one dp3 instruction, arbitrary attenuation function can be implemented.