1. A method for computing plane equations for graphic primitives, comprising: computing a z plane equation for each one of the graphics primitives using z attributes of each vertex of a graphics primitive; rasterizing each one of the graphics primitives at a coarse level to produce coarse z values by evaluating the z plane equations; culling one or more of the rasterized graphics primitives based on the coarse z values to produce remaining graphics primitives; computing, after producing the remaining graphics primitives, a non-z plane equation for each one of the remaining graphics primitives using a different attribute of each vertex of the graphics primitive; and shading the remaining graphics primitives by evaluating the non-z plane equations to produce an image.