This morning I will continue describing Mesa3D's Radeon200 driver with it's "span" methods. Which are attached to a dispatch table for the SoftWare RASTerizer (swrast).
To start the span renderer, it flushes any vertices to the GPU before memory mapping all textures, the framebuffer for the swrast, and maybe the read buffer.
Finishing the span renderer involves flushing the swrast (writing out these spans with reencodings) and unmapping all those textures.
Fin, until tonight.
For people who care about, support, or build Free, Libre, and Open Source Software (FLOSS).