Scanline rendering is a rendering algorithm in 3D computer graphics
that works on a point-by-point basis rather than polygon-by-polygon basis. Some point in a line is calculated, followed by successive points in the line.
When the line is finished, rendering proceeds to the next line.
The asset of this method is that it is not necessary to translate the coordinates of all vertices from the main memory into the working memory area each time a new polygon is encountered -- it's probable that some of the vertices have already been loaded in memory from neighboring polygons. The main memory is often very slow compared to the link between the central processing unit and cache memory, and thus avoiding re-accessing vertices in main memory can provide a substantial speed-up.
This kind of algorithm can be easily integrated with the Phong reflection model and Z-buffer algorithm.
Scanline rendering is used by most modern graphics cards and is typically accessed by the programmer using some 3D API such as OpenGL or Direct3D.