Clip circuit for CRT display unit

Claim 1

A clip circuit for CRT display unit, in which portions outside a predetermined area displayed on the CRT screen are clipped from a line segment extending from the inside of said predetermined area to the outside of said area or from the outside of said area into said area, said clip circuit comprising: line segment data providing means (20) for providing data representing start point coordinates and end point coordinates of said line segment, area data providing means (21) for providing data representing border lines of said predetermined area, ratio calculating means (82) for calculating a ratio of a distance between the start point coordinates and the end point coordinates of said line segment to a distance between the start point coordinates or the end point coordinates and one of the border lines of said predetermined area, based on the line segment data provided from said line segment data providing means (20) and the data representing the border line provided from said area data providing means (21), determining means (SP24, SP26, SP54, and SP56) for determining whether or not the ratio calculated by said ratio calculating means (82) is larger than a predetermined value, coordinates setting means (SP32, SP35, SP37 and SP40) for setting new start point coordinates or new end point coordinates in the vicinity of a point of intersection . between said line segment and said border line of said predetermined area instead of said start point coordinates or end point coordinates of said line segment, in response to determination by said determining means that said ratio is larger than said predetermined value, and intersection point calculating means (SP27) for calculating a point of intersection between the line segment connecting said new start point coordinates and said end point coordinates or the line segment connecting said start point coordinates and said new start point coordinates and said border line of said predetermined area by a middle point division method, based on said new start point coordinates or new end point coordinates set by said coordinates setting means and the data representing the border line provided from said area data providing means (21).