ABSTRACT
This chapter explains how to reduce the number of hardware-accelerated percentage closer filtering (PCF) texture operations for conventional shadow map filtering. Conventional shadow filtering works by directly filtering binary visibility results obtained from a depth-only shadow map. Most games still make use of conventional uniform shadow filters. The chapter explores the various conventional shadow filtering techniques, and presents two exemplary techniques that use a filter matrix with nonseparable weights. These techniques reduce the number of necessary PCF texture operations from (N -1) × (N -1) to (N/2) × (N/2) for uniform (*) and separable shadow filters. The chapter Illustrates an algorithm to implement box filters with nonseparable unique weights in only (N 1) × (N/2) instead of (N 1) × (N 1) PCF texture operations. In order to achieve physically plausible shadows, percentage closer soft shadows (PCSS) were introduced as a real-time method to achieve contact hardening shadows.
