A superior graphic processing device is provided that performs parallel and fast edge function processing for coverage calculations during an anti-aliasing process. The edge function for each sub-pixel of a pixel can be described separately for the base edge function Bef concerning pixel coordinates, and the sub-edge function Sef concerning sub-pixel references, and when the sum of the values for the edge functions Bef and Sef is substituted as a variable for evaluation function LineIOcheck, whether a sub-pixel is located above, below, or on an edge line can be determined. &Dgr;x