| 摘要 |
The system forms displays as an array of picture elements each of which can have more than two possible intensities (e.g. a grey scale). The circle generator derives the intensities for elements in and near an arc of a circle to be drawn. The intensity for an element is determined by the closest distance d from the element to an ideal circle characterizing the arc in such a way as to give a smoothed appearance. The distance d is obtained from a distance accumulator (39) and applied, adjusted for the width of the arc, to a sample table (42) holding the intensities. A step sequencer (40) causes the circle generator to execute scans along lines of picture elements across the arc. At each step d is changed by a distance increment or decrement obtained from one or both of two increment accumulators (36) and (37). These in turn are changed at each step by a constant amount obtained from a register (38) and equal to the step size divided by the radius of the ideal circle. Arcs are bounded by radial lines and may be abutted. |
