an apparatus is disclosed for displaying arbitrary forms on a raster - scanned cathode ray tube converting the analog x and y deflection voltages of the raster signal directly into a digital ttl level blanking signal . the circuit designer , utilizing cartesian or polar coordinates , specifies a desired shape and its location utilizing the appropriate formulas . in this manner , a number of raster cut - out circuits are readily coupled to define a desired number of arbitrary shapes on a raster scanned cathode ray tube .