Rasterization is the process of converting primitives like lines and triangles (already converted into window coordinates by the transformation stage) into updates to pixel values in the window's drawable frame buffer region. OpenGL's rasterization stage can be divided into four sub-stages: primitive decomposition, texturing, fog, and per-fragment operations.
Figure 3: Example of decomposing a smooth shaded polygon to spans, then
iterating across the span, interpolating depth and color between the
endpoints.