| 摘要 |
PURPOSE:To segment the part of a polygon in a display range at high speed by outputting a dot or side in a boundary and coordinate values at an intersection point in the boundary from the output code of a position deciding circuit outputting a code showing whether one side of the polygon lies within the boundary, outside the boundary or intersects. CONSTITUTION:The contents of the register 74 of the position deciding circuit 61 and those of a register 75 show the position relationship between the larger boundary and the side, and that between the smaller boundary and the side, respectively. Two types of four bit information of the registers 74 and75 are converted into two-bit code identifying whether the side lies within the display range, outsides said range or intersects with the aid of a decoder 76. Due to the output result of the decoder 76, a clipping processor 62 does not output the side outside the boundary, and omits it from a display subject. When the side lies within the boundary, including start and end points of the side, the processor 62 outputs the coordinates of the start point, stores them in the memory area of a data buffer 66 and clips the coordinates in the next coordinate axial direction. Eventially only vertex coordinates of the polygon clipped in X and Y directions are stored in the data buffer 66.
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