gen6+ uses _mesa_base_format_has_channel() to check for the alpha
channel, while gen4-5 use ctx->DrawBuffer->Visual.alphaBits. By using
_mesa_base_format_has_channel() here we keep the same behavior accross
all gen.
While initially both ways of checking the alpha channel seemed correct
to me, this change also seems to fix fbo-blending-formats piglit test on
gen4.
Signed-off-by: Rafael Antognolli <rafael.antognolli@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Rafael Antognolli
5246d3eb83