On Tuesday, December 29, 2015 6:42:58 PM PST Marek Olšák wrote: > On Mon, Dec 28, 2015 at 11:28 PM, Kenneth Graunke <kenn...@whitecape.org> wrote: > > Unigine Heaven 4.0 and Valley 1.0 use dual color blending but don't > > specify which fragment shader output is which, so there's at best a > > 50/50 chance of us guessing it correctly. This is invalid. > > > > Unigine fixed this in 4.1 and 1.1 versions over a year and a half ago, > > but hasn't actually released them for whatever reason. So, add the > > workaround back so that it works for most people. > > > > Fixes Heaven 4.0/Valley 1.0 rendering on Ivybridge. For whatever > > reason, Broadwell worked. 4.1 and 1.1 have always worked. > > > > Signed-off-by: Kenneth Graunke <kenn...@whitecape.org> > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92233 > > Cc: mesa-sta...@lists.freedesktop.org > > Cc: Marek Olšák <marek.ol...@amd.com> > > Hi Ken, > > We've never had a problem with this in gallium, but if it's just luck, > I suppose it's okay to add the workaround. > > In Gallium, the second color output is the same as gl_FragData[1], so > it doesn't matter how the location is specified as long as it's clear > which output goes second. > > How difficult is it to be unlucky here? Does it depend on IR node ordering? > > Reviewed-by: Marek Olšák <marek.ol...@amd.com> > > Marek
Their shader has two ordinary user-defined outputs: out vec4 s_frag_data_0; out vec4 s_frag_data_1; But they don't call glFragDataLocationIndexed() to define which output variable is color 0 and which is color 1. Nor do they use a layout qualifier. So, both variables end up with var->data.index == 0. Which means they've told us both outputs are SRC0, and there isn't a SRC1. We could guess based on the variable ordering - s_frag_data_0 happens to be first (unless we reorder the IR nodes for some reason). Or, we could guess based on the variable names. It's been 2.5 years since I first debugged this, so I don't recall what the location field was set to. If they set it to N and N + 1, we could assume that they meant color index 0/1 based on that. If it's the same, we're out of luck. (In GL, location is *supposed* to mean the render target index, because you can in theory do MRT and dual source blending together. But, nobody's hardware does, AFAIK.) --Ken
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