Bresenham’s line algorithm is a line drawing algorithm that determines the points of an n-dimensional raster that should be selected in order to form a close approximation to a straight line between two points. - wikipedia / HN / pdf

see also

• Line drawing on a grid (redblog)
• Midpoint circle algorithm - Bresenham’s circle algorithm is derived from the midpoint circle algorithm.
• Bresenham or Fixed point ? - search in page
• How to draw ugly lines really fast - subpixel coordinates drawing and Bresenham enhancement discussed.