| 摘要 |
PROBLEM TO BE SOLVED: To make plotting processing fast and to enlarge and reduce a display picture at an arbitrary position and so on by improving a trapezoidal painting- out method. SOLUTION: Among intersections formed between a drawn segment and the border line of a display object area, an intersection formed when the plotting segment enters the display object area is specified as a 'incoming line point' and an intersection formed when the plotting segment exits from the display object area is specified as an 'outgoing line point'. For plotting processing including the right end, a 1st rule for drawing an auxiliary line for trapezoidal painting from the top part of the right end line to respective incoming/outgoing line points of the plotting segment on the right end line each time an incoming or outgoing line point appears is set. In the final stage of the plotting, a 2nd rule for selectively plotting a painting-out auxiliary line over the entire area of the right end line is set according to a specific rule based upon a combination of whether the incoming/outgoing line point at the top on the right end line is an incoming line point or outgoing line point and whether the total number of incoming and outgoing line points on the right end line is even or odd. |
