Abstract: A vector generator (11) for a computer graphics system of the type in which the beam (26) of a CRT (13) is deflected by analogue deflexion signals to form an image comprised of a plurality of discrete vectors each defined, in each of two, orthogonal deflexion axes, the first and second digital words respectively defining the initial position and the length of the vector. The vector generator (11) includes circuitry (43, 44) that ensures that each vector is drawn with substantially uniform brightness regardless of the length of the vector. Additional circuitry (42, 54) is furnished so that an instantaneous indication may be obtained of a light pen (19) strike or the occurrence of edge violations. This circuitry (42, 54) also yields continuous digital information concerning the current beam position.