Ian Romanick wrote:Roland Scheidegger wrote:
this new demo fails pretty horribly on r200. It seems to be caused
by the same bug as I reported here, http://marc.theaimsgroup.com/?l=dri-devel&m=107854279829216&w=2, something fundamental just doesn't work right with regard to
blending. Even if you never enable blending (or disable it
explicitly) in this blendminmax demo, the results are vastly
different to software rendering (blend equation seems to make a
difference even if blending is disabled for some reason).
You beat me to the punch. :) When I wrote that test I was 99% sure it would fail on R200 the same way it failed on i830. The problem is that the GL_MIN and GL_MAX modes do *NOT* use the values set by glBlendFunc (or glBlendFuncSeparate). If the blend equation is set to GL_MIN or GL_MAX, it is supposed to operate as if 'glBlendFunc(GL_ONE,GL_ONE)' was set.
Ah, missed that in the spec. Seems to be unnecessarily restrictive to
not have a weighting factor for GL_MIN/MAX, apparently common hardware could do it just fine (or maybe it doesn't make enough sense to allow it?).
Modern hardware can, but that extension is almost 10 years old. I don't think hardware was quite as orthogonal back then. :)
This does not explain though why the results are wrong if blending isn't enabled in the first place, since neither blend function nor blend equation should change anything if blending is disabled, I think.
Yeah, that's probably a different problem. :( The r200 may not have a way to actually disable blending. It might be that the hardware has to be set to an equation of GL_ADD and functions of GL_ONE and GL_ZERO. Dunno.
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