Abstract: A method of filling a polygonal region enables a polygon of any shape to be filled with pixels with a simple algorithm. A display memory area and a working area each having a plurality of addresses correponding to all the pixels on a display screen are provided. A minimum rectangular area including the polygon is determined in accordance with all the polygon vertices, and the minimum rectangular area within the working area is cleared. A straight line (or an edge) connecting each pair of adjoining vertices of the polygon is described to the display memory area with predetermined values. The edges are also described to the working area but in accordance with three rules. Under Rule 1, when a constituent dot of the edge is described to the corresponding address, the data in the address is inverted. Under Rule 2, a start constituent dot of each edge is described only when the edge to be described has an inclination different in polarity from the precedingly described edge.