Clip circuit of CRT display units

Claim 2

A clip circuit of a CRT display unit for clipping, out of a polygon, portions protruding from the three-dimensional space represented in the CRT screen at the time of inserting partially said polygon into said three-dimensional space, said clip circuit comprising: coordinate providing means (16) for providing three-dimensional coordinate data representing the respective vertexes of said polygon, three-dimensional plane data providing means (175) for providing data on the primary to tertiary planes forming said three-dimensional space, said primary to tertiary planes being respectively comprised of a pair of planes spaced by a predetermined distance, determining means (S2) for determining, based on the three-dimensional coordinate data from said coordinate providing means and the data from said three-dimensional plane data providing means, whether the respective vectors represented by said three-dimensional coordinate data and constituting said polygon exist between the pairs of said three-dimensional planes, first extracting means (S3) responsive to the determination of nonexistence of the vectors in the pairs of said three-dimensional plane by said determining means, for extracting from the respective vectors, a line segment existing in the pair of said primary planes based on the respective vectors and the data on the pair of said primary planes provided from said three-dimensional plane data providing means, so that coordinate data representing said line segment are provided as output and the other line segments excluding said line segments are clipped off, second extracting means (S7) responsive to the output from said first extracting means, for extracting a line segment existing in the pair of said secondary planes, from said line segment extracted by said first extracting means, and based on the data on the pair of secondary planes provided from said three-dimensional plane data providing means, so that the coordinate data representing said line segment are provided as the output and the other line segments excluding said line segment are clipped off, third extracting means (Sll) responsive to the output from said second extracting means, for extracting a line segment existing in the pair of said tertiary planes, from said line segment extracted by said second extracting means, and based on the data on the pair of tertiary planes provided from said three-dimensional plane data providing means, so that the coordinate data representing said line segment are provided as the output and the other line segments excluding said line segment are clipped off, and output means (S15) responsive to said first to third extracting means for providing the coordinate data representing said line segments extracted by said first to third extracting means.

Claim 3

A clip circuit of a CRT display unit in accordance with claim 1, wherein said first extracting means comprises: first vector calculating means (S21 to S27) responsive to the output from said determining means, for calculating, based on the respective vectors and connecting the vertexes of said polygons and the data on the pair of said primary planes, a vector extending from the outside of a field bounded by the pair of said primary planes into said field and a vector extending from the inside of said field to the outside, out of the respective vectors connecting the vertexes of said polygon. first intersection point calculating means (S31 and S39) responsive to the output from said first vector calculating means, for calculating, based on said calculating vectors and the data on the pair of said primary planes, intersection points at which said calculated vectors cross either of the pair of said primary planes and primary polygon extracting means (S32, S33, S35 to S37 and S40 to S42) responsive to the output from said first intersection point calculating means, for extracting, based on said calculating intersection points and the data on the pair of said primary planes, a polygon represented by the line segments connecting said calculated intersection points and the vectors existing in the field bounded by the pair of said primary planes, said second extracting means comprises: second vector calculating means (S21 to S27) responsive to the output from said primary polygon extracting means, for calculating, based on said respective vectors and the data on the pair of said secondary planes, a vector extending from the outside of a field bounded by the pair of said secondary planes into said field and a vector extending from the inside of said field to the outside, out of the vectors connecting the vertexes of said polygon extracted by said primary polygon extracting means, second intersection point calculating means (S31, and S39) responsive to the output from said second vector calculating means, for calculating, based on said calculated vectors and the data on the pair of said secondary planes, intersection points at which said calculated vectors cross either of the pair of said secondary planes, and secondary polygon extracting means (S32, S33, S35 to S37 and S40 to S42) responsive to the output from said second intersection point calculating means, for extracting, based on said calculated intersection points and the data on the pair of secondary planes, a polygon represented by the line segments connecting said calculated intersection points and the vectors existing in the field bounded by the pair of said secondary planes, and said third extracting means comprises: third vector calculating means (S21 to S27) responsive to the output from said secondary polygon extracting means, for calculating, based on said respective vectors and the data on the pair of said tertiary planes, a vector extending from the outside of a field bounded by the pair of said tertiary planes into said field and a vector extending from the inside of said field to the outside, out of the vectors connecting the vertexes of said polygon extracted by said secondary polygon extracting means, third intersection point calculating means (SS1 and S39) responsive to the output from said third vector calculating means, for calculating, based on said calculated vectors and the data on the pair of said tertiary planes, intersection points at which said calculated vectors cross either of the pair of said tertiary planes, and tertiary polygon extracting means (SS2, S33, S35 to S37 and S40 to S42) responsive to the output from said third intersection point calculating means, for extracting, based on said calculated intersection points and the data on the pair of said tertiary planes, a polygon represented by the line segments connecting said calculated intersection points and the vectors existing in the field bounded by the pair of said tertiary planes.

Claim 4

A clip circuit of a CRT display unit in accordance with claim 2, wherein said first vector calculating means comprises means (S24 to S27) for determining, based on the differences between the coordinates data representing the respective vertexes of said polygon and the data representing the respective planes of the pair of said primary planes, whether the vectors connecting the respective vertexes exist in the field bounded by the pair of said primary planes or extend from the inside of said field to the outside or extend from the outside into said field, said second vector calculating means comprises means (S24 to S27) for determining, based on the differences between the coordinate data representing the respective vertexes of said polygon extracted by said primary polygon extracting means and the data representing the respective planes of the pair of said secondary planes, whether the vectors connecting the respective vertexes exist in the field bounded by the pair of said secondary planes or extend from the inside of said field to the outside or extend from the outside into said field, and said third vector calculating means comprises means (S24 to S27) for determining, based on the differences between the coordinate data representing the respective vertexes of said polygon extracted by said secondary polygon extracting means and the data representing the respective planes of the pair of said tertiary planes, whether the vectors connecting the respective vertexes exist in the field bounded by the pair of said tertiary planes or extend from the inside of said field to the outside or extend from the outside into said field.

Claim 5

A clip circuit of a CRT display unit in accordance with claim 2, wherein said primary polygon extracting means comprises means (S5) for substituting any one of said calculated intersection points for the first start point coordinates and the final end point coordinates in case where the first start point coordinates and the final end point coordinates of said extracted polygon do not exist in the field bounded by the pair of said primary planes, said secondary polygon extracting means comprises means (S9) for substituting any one of said calculated intersection points for the first start point coordinates and the final end point coordinates in case where the first start point coordinates and the final end point coordinates of said extracted polygon do not exist in the field bounded by the pair of said secondary planes, and said tertiary polygon extracting means comprises means (S13) for substituting any one of said calculated intersection points for the first start point coordinates and the final end point coordinates in case where the first start point coordinates and the final end point coordinates of said extracted polygon do not exist in the field bounded by the pair of said tertiary planes.