Precision hardware circular-arc generation for computer graphic-display systems using line-segment-data

For advanced graphics, it is required that both general and circular functions should be displayed, in addition to alphanumeric and line diagrams. For general functions, software is used, owing to the low frequency of occurrence of general functions on display diagrams. For circular functions, this is not the case, and there is a need for hardware generation with scaling, windowing and scissoring properties. Further, for precision, the circular arc should start and finish exactly on the m × m screen matrix, with points on the drawn arc within one increment of the true arc. This paper describes the generation of arcs by hardware, using successive line-segment data that satisfy the error equations. These errors are derived, and a computer simulation of the hardware logic design is used to analyse the errors and to determine the bit redundancy in the ¿¿2/2 registers. The final design is capable of generating circular arcs within the prescribed error limits at high generation speeds. The generator may be included in any display system that possesses accurate line-drawing facilities.