ABSTRACT
We have seen in Chapter 3 that image-based hard shadows are prone to aliasing. Recall that errors due to the discrete shadow-map sampling can be categorized into initial sampling errors (which happen when creating the shadowmap) and resampling errors (which happen when rendering using the shadow map). Chapter 4 showed several approaches to reduce initial sampling error (i.e., undersampling) by adapting the shadow-map resolution in various manners. In this chapter, we will discuss several ltering methods for shadow mapping,
which are mainly useful for reducing resampling error. Furthermore, ltering is also oŸen used to make undersampling artifacts less pronounced by smoothing or blurring the shadow boundaries. In fact, simple upscaling techniques for lowresolution images also rely on lters to remove the quad appearance induced by the pixels of the input image. At second glance, this becomes even more interesting because it results in shadow boundaries that resemble to some extent the appearance of physically based soŸ shadows at a much lower computational ešort. However, none of the followingmethods in this chapter give physicallymeaningful soŸ shadows-their main purpose is to address the aliasing problem e›ciently. In practice, most of the techniques presented in this chapter, as well as their
extensions, which we will discuss in Section 6.5.3, are standard solutions in game contexts and are of high practical value.e simplicity of the implementation, the relatively good performance, the simple tradeoš between performance and quality, and the reasonable outcome (at least for most congurations) make them usually a good choice. e interested reader is also referred to the talk byBavoil atGDC08 [Bavoil08a].
is talk summarizes many of the practical implementation aspects and serves as a good overview for the techniques that will be presented in this chapter. We will rst discuss why ltering shadow maps needs special attention (Sec-
tion 5.1), then show the applications of ltering (Section 5.2), namely blurring,
