Method and apparatus for automatically determining the x-y intersection

Abstract

A method and apparatus for determining the X--Y coordinates on the raster of the intersection of two curves one of which is stored in the display system raster refresh buffer. The second curve is generated by a curve generator or some other source of sequential X--Y coordinate data defining the X--Y coordinates on the raster where the second curve would lie. As each X--Y coordinate is generated by curve generator it is translated into a buffer address and the contents of that address in the buffer memory are accessed and a determination is made to see if said first curve exists at that address. If an element of the first curve is found to exist in the buffer store at the generated address location, it is known an intersection point has been found and the appropriate X--Y address is gated from the system to utilization means. According to a further feature of the invention, if a plurality of intersection points are found for two particular curves, averaging means are provided for at least approximating the midpoint of the actual intersection of the two curves and said midpoint address is gated out of the system as the intersection point. A method and means are also provided for determining if two curves have a point of tangency when they exist on two adjacent raster lines but do not actually intersect.