| 摘要 |
When a main figure coming on top and at least one sub-figure following the main figure are designated among superposed figures displayed on a screen, a processor is operated through a program control to find an intersecting point at which a figure element of the main figure intersects a figure element, such as line segment, of the sub-figure. When such an intersecting point exists, the figure element is divided at the intersecting point into sub-figure elements, and the hidden-line flag in the data on the sub-figure element behind the main figure is turned on. The hidden line processing is effected for the whole figure elements of the sub-figure. When the picture is reproduced the portions having hidden-line flags turned on are not produced or displayed on the display screen. When a figure element does not intersect any figure element of the main figure, it is checked whether a starting point of the figure element is inside or outside the main figure. When it is inside, the hidden-line flag of the element is turned on so that it is not drawn on the display screen. |
