An approach to real-time scan conversion

Scan conversion—that is, the transformation of line segment endpoint coordinates into a collection of scanline segments suitable for raster display—is important because raster displays have many advantages over random-scan, or calligraphic, displays. The calligraphic displays require extensive special-purpose hardware to generate line segments, or "vectors," and to drive the beam deflection circuits of the CRT. Furthermore, by its very nature, the calligraphic display is subject to damage caused by software defects; a program which directs the beam to the same portion of the CRT face for too long can damage the phosphors, creating a permanent dark spot.