1. A method comprising: selecting, with a graphics processing unit (GPU), a rasterization mode for a graphics primitive from a set of at least two candidate rasterization modes based on a metric indicative of an area of the graphics primitive, the set of at least two candidate rasterization modes including a first candidate rasterization mode and a second candidate rasterization mode; performing, with fixed function scan conversion hardware of the GPU, scan conversion for the graphics primitive when the first candidate rasterization mode is selected as the rasterization mode for the graphics primitive; and performing, with a programmable shader unit of the GPU, scan conversion for the graphics primitive when the second candidate rasterization mode is selected as the rasterization mode for the graphics primitive, wherein the programmable shader unit is configured to scan convert multiple primitives in parallel.