An image generator including a visible edge encoder which receives information defining the visible surfaces of a two-dimensional projection of a three-dimensional world and provides encoded two-dimensional visible edges which are x-ordered and are ready for transmission to a plurality of display terminals. The information received by the visible edge encoder defines the x and y intercepts, in successive planes which include the observer's eye and successive scanlines, of all three-dimensional edges which would be visible to the observer. The information provided by the visible edge encoder is edges which represent a two-dimensional projection of three-dimensional objects, each edge defined by its intended position on a two-dimensional screen and by attributes for a portion of the screen adjacent the edge, such as color, brightness, shading and the like. The edges which are provided by the visible edge encoder and are transmitted to the display terminals, where they are decoded into video raster points, are a highly compressed representation of a video raster; hence, the communication link between the image generator and the terminals can have a relatively low capacity, and the same image generator can service a substantial number of display terminals.
Image generator for a multiterminal graphic display system