Commit 0d4aa5f55f introduced the watermark to optimize the guardband
state changes and always computed new_distance as MAX2(distance,
watermark).
That is correct for point/line paths where distance > 0, but it keeps a
non-zero discard distance alive when the next draw sets distance = 0
(triangles). This leaks wide point/line clip-discard state into later
triangle draws and can clip away large parts of geometry (as observed in
Sauerbraten). Only apply the watermark when distance > 0 and reset it to
zero otherwise so triangle draws disable clip-discard as intended.
Fixes: 0d4aa5f55f ("r300: pop-free clipping")
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/14959
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40223>
ce33f82f83