Efficient tile-aware bounding-box overlap test for tile-based rendering

Tile-based rendering appears to be a promising technique for low-cost, low-power 3D graphics platforms. This technique decomposes a scene into tiles and renders the tiles independently. It requires, however, that the primitives are sorted into bins that correspond to the tiles, which can be very time-consuming and may require a lot of memory bandwidth. The most often used test to determine if a primitive and a tile overlap is the bounding box test. This test checks if the 2D axis aligned bounding box of the primitive overlaps the tile and comprises four comparisons in the worst case. In this paper, we show that the efficiency of the bounding box test can be improved significantly by adaptively varying the order in which the comparisons are performed, depending on the position of the current tile. Experimental results obtained using several 3D graphics workloads show that the dynamic bounding box test reduces the average number of comparisons per primitive by 26% on average compared to the best performing static version in which the order of the comparisons is fixed.