Moment Shadow Mapping

Figure 1: Filtered hard shadows produced by various techniques. Moment shadow mapping provides a high quality heuristic for the result of percentage closer filtering using one shadow map sample per fragment and 64 bits per shadow map texel. Variance and exponential shadow mapping are faster requiring only 32 bits per texel but produce more artifacts (red arrows). Rendering without shadows takes 0.64ms. We present moment shadow mapping, a novel technique for fast, filtered hard shadows. Like variance shadow mapping it allows for the application of all kinds of efficient texture filtering and antialias-ing to its moment shadow map. However it is designed to provide a substantially higher quality. Moment shadow maps store four mo-ments of the depth within the filter kernel. Using this information, our efficient algorithm computes the sharpest possible lower bound as approximation to the shadow intensity. The choice to compute such a bound using four moments is based upon an automated eval-uation of thousands of alternatives and thus known to be optimal. To reduce memory and bandwidth requirements we present an opti-mized quantization scheme to allow 16-bit quantization of moment shadow maps. Our evaluation demonstrates that moment shadow mapping produces high quality results with a single shadow map sample per fragment using 64 bits per shadow map texel