Z² traversal order for VR stereo rendering on tile-based mobile GPUs

With increasing demands of virtual reality (VR) applications, efficient VR rendering techniques are becoming essential because VR stereo rendering requires increased computational costs to separately render views for the left and right eyes. To reduce the rendering cost in VR applications, we present a novel traversal order for tile-based mobile GPU architectures, called the Z² traversal order. In tile-based mobile GPU architectures, a tile traversal order that maximizes spatial locality can increase the GPU cache efficiency. For VR applications, our approach improves the traditional Z-curve order; we render two screen tiles in the left and right views by turns or simultaneously, as a result, we can exploit spatial locality between the two tiles. To evaluate our approach, we conducted a trace-driven hardware simulation using Mesa and a hardware simulator. The experimental results show that the Z² traversal order can reduce external memory bandwidth requirements and can increase rendering performance.