mesa: st_draw_feedback shaders broken
I've been trying to figure out an issue I've been having with shader lowering for a while: basically if I alter i/o in the wrong way, I end up failing the piglit rasterpos tests. Except these tests don't go through the running driver. Instead, they go through st_feedback_draw_vbo
, which binds the current shaders to the draw module, which has an entirely different set of expectations than every other driver. This is why many drivers end up failing tests which use it.
Anything from the mesa frontend which goes through the draw module needs to essentially NOT go through any driver-based lowering, and it needs to use all the pipe caps specific to llvmpipe. Anything else is prone to failure.