Alphatest vs Blend

[DaViper]

I was wondering if anyone could tell me if

glEnable(GL_ALPHA_TEST);
glAlphaFunc(GL_EQUAL, 1.0);

is faster than

glEnable(GL_BLEND)
glBlendFunc(GL_ONE_MINUS_DST_ALPHA,GL_ZERO);

in my application both calls have similar effects, so i would like to know which one is faster.

Chris

[DFrey]

Generally the alpha test will be a bit faster if blending is disabled.

[MikeC]

IIRC, in the SGI software renderer for Win32 (and possibly in the MS one too) alpha blend is on the fast path and alpha test isn't, so in software you might see alpha blend running faster. In general though, as DFrey says, testing should be faster. Blending requires a read-modify-write round trip to the framebuffer whereas testing doesn't, so theoretically alpha test requires only half the memory bandwidth.

[DaViper]

thx for the replies, both of you confirmed what i thought