I believe these guys are actually going straight from SQL to "GPU instruction code" (so AIUI the SQL query execution is not some hack that is layered on top of

I believe these guys are actually going straight from SQL to "GPU instruction code" (so AIUI the SQL query execution is not some hack that is layered on top of the programmable shader pipeline [which is what's responsible for the "here is a list of vertices now draw me a 3d scene part" you mentioned] or something like that but runs directly on the more or less general purpose processor in the graphics card) I understand the part where they "map the result set to opengl primitives" as that they write the output/result set of the sql query into some datastructure that allows them [after executing the query] to easily use it from opengl to render pretty stuff. This part shouldn't be much different from other texture/vertex data that you'd bring in e.g. from files on disk or a MySQL database into opengl specific buffers so that you can subsequently use it for drawing in your program.