Polygon engine for updating computer graphic display employing compressed bit map data

A method of rendering a plurality of objects which form a computer graphic display into a frame buffer having a plurality of scan lines comprising the steps of:

• specifying the objects into a list for the next frame of the display, each object comprising a plurality of pixels, each pixel of the object having an identical color;
• converting each object of said list of objects into a list of spans, each span corresponding to a horizontal line of the display for the next frame, each span defining a group of horizontally adjacent pixels of a corresponding single object in terms of horizontal offset, pixel count, depth, and color;
• merging said list of spans for all objects of said list of objects into a single master list of spans, whereby each span for each object for a particular horizontal line appears in said master list of spans for that horizontal line;
• resolving the depth of said spans in said master list by choosing the color for each span of overlap from the overlapping span having the least depth value;
• converting said master list of spans into a set of run-length-encoded bit map lines for the next frame, each run-length-encoded bit map line defining all sets of horizontally adjacent pixels having the same color, each set including the number of pixels and the color for that set;
• and
• updating the frame buffer by writing each run-length-encoded bit map line into a corresponding scan line of the plurality of scan lines in the frame buffer.