A basic scan conversion for straight line and two developed algorithms are proposed in this paper. Different from other proposed algorithms, the basic algorithm is constructed with controlling iterations directly by residuals rather than intermediate measures. This makes the algorithm easier to be derived, and easier to be developed to an integral antialiasing drawing algorithm. Furthermore, a kind of simple and efficient run-length algorithm for scan conversion of line is derived. These algorithms are not only with a high speed for drawing a line, but also are easy to be derived and understood. All these algorithms are highly suitable for teaching too.