Two-phase load distribution for rendering large 3D models on a graphics cluster

In this paper we address the problem of distributing rendering computations for real-time display of very large 3D models using a graphics cluster. With a programmable graphics processing unit (GPU) in each node, rendering computations are increasingly carried out in two phases using two separate GPU programs: a vertex shader program for vertex (geometry) processing and a fragment shader program for pixel (color) processing. With fragment shader programs becoming more and more time consuming for increased realism and special visual effects, distributing load solely based on geometry as is done in most contemporary systems can cause significant load imbalance. There is often only a weak correlation between geometry and pixel data distribution, due to multiple factors such as occlusion of objects behind, by objects in front. Clearly, load balancing for geometry processing or pixel processing alone is not optimal. In this paper, we present a novel in-frame two-phase load-balancing technique that distributes data first for geometry and then for pixel processing. The technique is implemented on a graphics cluster and experimental results demonstrate considerable improvements in rendering performance.