Global Illumination using Imperfect Volumes

This paper introduces the concept of imperfect volumes, a fast one-pass point-based voxelization algorithm, and presents its applications to the global illumination problem. As often noted, diffuse indirect illumination has the characteristics of a low frequency function, consisting of smooth gradations. We exploit this by performing the indirect lighting computations on a rough approximation of the scene, the imperfect volume. The scene is converted on the fly to a dense point cloud, and each point is directly rendered to a volume texture, marking the corresponding voxel as occupied. A framebuffer reprojection scheme ensures that voxels visible to the main camera will get more points. Ray-marching is then used to compute the ambient occlusion or the indirect illumination of each voxel, and the results are stored using spherical harmonics. We demonstrate that the errors introduced by the imperfections in the volume are small and that our method maintains a high frame rate on scenes with high geometric complexity.