A Memory-Efficient Unified Early Z-Test

The Unified Early Z-Test (U-EZT) is proposed to examine the visibility of pixels during tile-based rasterization in a mobile 3D graphics processor. U-EZT combines the advantages of the Z-max and Z-min EZT algorithms: the Z-max algorithm is improved by the independently updatable z-max tiles and the use of mask bits; and the Z-min algorithm is improved by reusing the mask bits from the z-max test to update the z-min tiles after tile rasterizing. As a result, storage requirements are reduced to 3 bits per pixel, and simulations suggest that U-EZT requires 20 percent to 57 percent less memory bandwidth than previous EZT algorithms.