Fast Radiosity Repropagation For Interactive Virtual Environments Using A Shadow-Form-Factor-List

Abstract

The radiosity method became a very important tool in order to enable photorealistic rendering in virtual reality systems. Based on the geometric description of a scene, the view-independent illumination is computed in a preprocess and colors are assigned to each patch vertex. These virtual environments look very impressive, but any interaction with the scene geometry or its materials results in a time expensive recalculation of the radiosity simulation. This leads to the common phrase:

Radiosity scenes are like museums, you may look around, but do not touch anything!

In this paper, a new algorithm is presented to overcome this problem. The algorithm is based on the fact that most of the information needed for the radiosity repropagation after any scene modification was already computed during the radiosity preprocess. Therefore, the radiosity method is extended by storing shadow- and form-factor-information in an efficient data structure, the so-called shadow-form-factorlist (SFFL). We describe how the SFFL can be used to minimize the recomputation time after any scene modification. Moreover, very important information about scene coherence is included within the SFFL. Thus, an efficient traversal of the SFFL helps to repropagate radiosity only in those parts of the scene, that are affected by the model change.