mesa/st: Lowering for clip distance
When PIPE_CAP_CLIP_PLANES
is 0, mesa/st automatically lowers user clip planes to clip distance writes via nir_lower_clip_vs
. However, drivers are unconditionally expected to handle clip distance, despite mobile hardware typically requiring clip distance lowered as well (via nir_lower_clip_fs
). Gallium should introduce a PIPE_CAP_CLIP_DISTANCE
cap, and if the CAP is 0, mesa/st should automatically call lower_clip_fs on relevant frag shader variants.
See !8953 (comment 799548) for context.