| 摘要 |
<p>A clip circuit (17) of a CRT display unit clips off, by means of a simple operation, the portion of a polygon (5) protruding from the three-dimensional space (4) when the polygon (5) is partially inserted into the three-dimensional space. More specifically, a window register (175) stores therein the data on the primary to tertiary planes forming the three-dimensional space, respectively comprised of a pair of planes. A host computer (10) provides three-dimensional coordinate data representing the respective vertexes of the polygon. An ALU (177) first extracts from the vectors constituting the polygon, a line segment existing in a field bounded by a pair of primary planes, according to the three-dimensional coordinate data from the window-register and the three-dimensional plane data from the host computer. Then, from the above stated line segment, the ALU (177) extracts a line segment existing in a field bounded by a pair of secondary planes and further extracts from this line segment, a line segment existing in a field bounded by a pair of tertiary planes, so that the other portions excluding the extracted line segments are clipped off. Accordingly, the unnecessary portions of a polygon can be clipped off only by one processing operation for each pair of primary to tertiaty planes, which means that only three processing operations are required.</p> |
