[Mesa-dev] [PATCH] i915g: fix incorrect gl_FragCoord value

[Stéphane Marchesin]

On Thu, Sep 22, 2016 at 8:40 AM, Emil Velikov <emil.l.velikov at gmail.com>
wrote:

> Hi Nicholas,
>
> On 26 August 2016 at 00:31, Nicholas Bishop <nbishop at neverware.com> wrote:
> > From: Nicholas Bishop <nicholasbishop at gmail.com>
> >
> > On Intel Pineview M hardware, the i915 gallium driver doesn't output
> > the correct gl_FragCoord. It seems to always have an X coord of 0.0
> > and a Y coord of the window's height in pixels, e.g. 600.0f or such.
> >
> > I believe this is a regression caused in part by this commit:
> > afa035031ff9e0c07a2297d864e46c76f7bfff58
> >
> > The old behavior used the output at index zero, while the new behavior
> > uses actual zeroes. In the case of gl_FragCoord the output at index
> > zero happened to be the correct one, so the behavior appeared correct
> > although the code already had a bug.
> >
> > Fixed by checking for I915_SEMANTIC_POS when setting up texCoords. If
> > the generic_mapping is I915_SEMANTIC_POS, look for the
> > TGSI_SEMANTIC_POSITION instead of a TGSI_SEMANTIC_GENERIC output.
> >
> > https://bugs.freedesktop.org/show_bug.cgi?id=97477
> > ---
> >  src/gallium/drivers/i915/i915_state_derived.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/src/gallium/drivers/i915/i915_state_derived.c
> b/src/gallium/drivers/i915/i915_state_derived.c
> > index 177b854..dbfbc84 100644
> > --- a/src/gallium/drivers/i915/i915_state_derived.c
> > +++ b/src/gallium/drivers/i915/i915_state_derived.c
> > @@ -145,7 +145,12 @@ static void calculate_vertex_layout(struct
> i915_context *i915)
> >        uint hwtc;
> >        if (texCoords[i]) {
> >           hwtc = TEXCOORDFMT_4D;
> > -         src = draw_find_shader_output(i915->draw,
> TGSI_SEMANTIC_GENERIC, fs->generic_mapping[i]);
> > +         if (fs->generic_mapping[i] == I915_SEMANTIC_POS) {
> > +            src = draw_find_shader_output(i915->draw,
> TGSI_SEMANTIC_POSITION, 0);
> > +         }
> > +         else {
> > +            src = draw_find_shader_output(i915->draw,
> TGSI_SEMANTIC_GENERIC, fs->generic_mapping[i]);
> > +         }
>
> Personally I'm unfamiliar with the i915g driver, so I've Cc'd Roland
> (the author of the commit 'breaking' this) and Stéphane (the author of
> this driver).
>
> Gents, any input on the above ?
>

It seems correct at a quick glance, but I'd like to investigate more. I
will do so when I'm back from vacation next week :)

Stéphane


> That said, please drop the unneeded brackets and add the following
> line in the commit message for v2.
> Cc: mesa-stable at lists.freedesktop.org
>
> Thanks,
> Emil
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> mesa-dev at lists.freedesktop.org
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>
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