An Approach to Global Illumination Calculation Based on Hybrid Cone Tracing

For 3D geographic information systems (GIS) or video game systems, global illumination (GI) effect can greatly improve the understanding of the volumetric structure and the spatial relationships of objects in the scene. However, GI effect is computationally expensive. It requires not only complex visibility computations between arbitrary points but also the integration computation over a large number of directions. These two computations become extremely difficult tasks for the real-time or interactive algorithms of the dynamic scene. This paper proposes a lightweight GI calculation approach built upon a hybrid cone tracing algorithm with which to approximate the GI effect of the open world scene in real time. First, the 3D scene is divided into two types: complex meshes and height-field meshes. Second, the corresponding lightmaps of the two meshes are generated and mipmaped, respectively. GPU hardware acceleration technology is used to do the calculation efficiently. Finally, a hybrid cone tracing method is performed on the GPU to gather the indirect lighting information for each shaded point. The method first carries out the cone-scene intersection test and then carries out the light sampling and accumulation calculation. All tracing calculations are based on the hybrid lightmap representation. In addition, the experiment results show the effectiveness of our method. Compared with the 3D texture VCT method, memory consumption can be reduced by up to 80% in our experiment.