1. A graphics processing subsystem operable to render a scene having a pixel represented by samples, comprising: a memory configured to store a geometry data structure associated with said pixel containing surface fragment coverage masks associated with said samples; and a graphics processing unit (GPU) configured to employ said surface fragment coverage masks to form a coverage matrix and carry out deferred shading on said pixel, wherein said GPU is further configured to rectify said coverage matrix such that said coverage matrix is symmetric before carrying out said deferred shading.