It turns out that BLEND_MIN and BLEND_MAX in Utgard take blend factors
into account. My guess is that actual equation looks like:
OP(As * S + Ad * D, Ad) for alpha, and
OP(Cs * S + Cd * D, Cd) for color.
So we have to set S factor to 1 and D factor to 0 to be compliant with
GL spec.
Fixes following piglit tests:
spec@!opengl 1.4@blendminmax
spec@arb_blend_func_extended@arb_blend_func_extended-fbo-extended-blend
(with patch my for ES2_compatibility and EXT_blend_func_extended)
Reviewed-by: Andreas Baierl <ichgeh@imkreisrum.de>
Reviewed-by: Erico Nunes <nunes.erico@gmail.com>
Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13873>