We demonstrate here the different uses of the Direct Acyclic Graph (DAG) refiner structure.
The most common refiner used in hierarchical radiosity is called the "BF refiner". It chooses wether the current hierarchical level is sufficient or if one element should be subdivided by using a simple threshold on a bidirectionnal estimation of the energy exchange. This already existing refiner has been redevelopped using the DAG structure. The BF-DAG is defined like that :
The BFA refiner is a BF-like refiner which takes into account the area of the elements. It was created to be used with special elements (like Sun & Sky). There is not a lot of difference between the algorithm but the way to compute energy exchanges. This BFA refiner has been redevelopped too with the graph structure, taking advantage of sharing nodes with the BF one. For example the Visibility estimation node is the same between BF and BFA, it is not necessary to create a new tool, just reuse the BF one. The BFA-DAG is defined like that :
The difficulty and the bottleneck of the refinement is the visibility estimation. BF is quite quick because the visibility is very strongly estimated. Using the graph structure it is possible to replace the visibility estimation tool of the BF-DAG by a more precise visibility tool. We use a combination of ray-casting and shaftculling in a new BF based refiner we called BFV.
This refiner reuses the Energy tool of the BF-DAG refiner, only the visibility part has been changed. It has been used to create complex images with a lot of indirect shadowing. It is a possible refiner of the "Virtual reality users" application scenario defined in WP3, because it creates images that are beautiful for the human eye and also for an immersed human. Here are some results :