| 摘要 |
A start point (x'0,y'0) and an end point (x'm,y'm) of a sub-line are obtained from a start point (x0,y0) and an end point (xm,ym) of a main line, and coordinate data of the start point (x'0,y'0) and the end point (x'm,y'm) are supplied to a DDA, so that a point array of the sub-line can be generated from the DDA. The main line is shifted along the x- or y-axis by one dot to obtain the sub-line. Intensity information from an intensity modulation circuit is noninverted/inverted in accordance with the main line/sub-line mode so as to provide a complementary relationship between the main line and the sub-line. A vector direction from the start point (x0,y0) to the end point (xm,ym) is detected to belong to one of the four areas obtained by dividing the x-y coordinate plane by lines y=x and y=-x when the start point (x0,y0) is defined as the origin of the coordinate system. In accordance with this detection, the start point (x0,y0) and the end point (xm,ym) are shifted by one (+1 or -1) along the x- or y-axis. These shifted points are used as the start point and the end point for interpolation and are supplied to the DDA. The DDA generates the sub-line obtained by shifting the main line by one dot in the upper direction (positive direction along the y-axis), the lower direction (negative direction along the y-axis), the left direction (negative direction along the x-axis), or the right direction (positive direction along the x-axis).
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