[Mesa-dev] [PATCH v4] i965/aa: fixing anti-aliasing bug for thinnest width lines - GEN6

[Predut, Marius]

> -----Original Message-----
> From: mesa-dev [mailto:mesa-dev-bounces at lists.freedesktop.org] On Behalf Of
> Ian Romanick
> Sent: Thursday, March 19, 2015 9:35 PM
> To: Predut, Marius; mesa-dev at lists.freedesktop.org
> Subject: Re: [Mesa-dev] [PATCH v4] i965/aa: fixing anti-aliasing bug for
> thinnest width lines - GEN6
> 
> On 03/19/2015 01:23 PM, Marius Predut wrote:
> > On SNB and IVB hw, for 1 pixel line thickness or less, the general
> > anti-aliasing algorithm give up - garbage line is generated.
> > Setting a Line Width of 0.0 specifies the rasterization of the
> > “thinnest” (one-pixel-wide), non-antialiased lines.
> > Lines rendered with zero Line Width are rasterized using Grid
> > Intersection Quantization rules as specified by bspec section 6.3.12.1
> > Zero-Width (Cosmetic) Line Rasterization.
> >
> > v2: Daniel Stone: Fix = used instead of == in an if-statement.
> > v3: Ian Romanick: Use "._Enabled" flag insteed ".Enabled".
> >     Add code comments. re-word wrap the commit message.
> >     Add a complete bugzillia list.
> >     Improve the hardcoded values to produce better results.
> >
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=28832
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=9951
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=27007
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=60797
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=15006
> >
> > Signed-off-by: Marius Predut <marius.predut at intel.com>
> > ---
> >  src/mesa/drivers/dri/i965/gen6_sf_state.c |   22 +++++++++++++++++++---
> >  1 file changed, 19 insertions(+), 3 deletions(-)
> >
> > diff --git a/src/mesa/drivers/dri/i965/gen6_sf_state.c
> > b/src/mesa/drivers/dri/i965/gen6_sf_state.c
> > index f9d8d27..91b46d9 100644
> > --- a/src/mesa/drivers/dri/i965/gen6_sf_state.c
> > +++ b/src/mesa/drivers/dri/i965/gen6_sf_state.c
> > @@ -367,9 +367,25 @@ upload_sf_state(struct brw_context *brw)
> >        float line_width =
> >           roundf(CLAMP(ctx->Line.Width, 0.0, ctx->Const.MaxLineWidth));
> >        uint32_t line_width_u3_7 = U_FIXED(line_width, 7);
> > -      /* TODO: line width of 0 is not allowed when MSAA enabled */
> > -      if (line_width_u3_7 == 0)
> > -         line_width_u3_7 = 1;
> > +
> > +      /* Line width of 0 is not allowed when MSAA enabled */
> > +      if (ctx->Multisample._Enabled) {
> > +         if (line_width_u3_7 == 0)
> > +             line_width_u3_7 = 1;
> > +      } else if (ctx->Line.SmoothFlag && ctx->Line.Width <= 1.49) {
>                                                                ^^^^ Based on
> the previous version of the patch, isn't that supposed to be 1.0?  Does this
> really not cause any piglit regressions?

No I don’t detected regression here.
(for line greater than this value we have the same situation like before and for lines thickness than 1.49 we are on the bugs)

> 
> > +         /* For lines less than 1 pixel thick, the general
> > +          * anti-aliasing algorithm gives up, and a garbage line is
> > +          * generated.  Setting a Line Width of 0.0 specifies the
> > +          * rasterization of the "thinnest" (one-pixel-wide),
> > +          * non-antialiased lines.
> > +          *
> > +          * Lines rendered with zero Line Width are rasterized using
> > +          * Grid Intersection Quantization rules as specified by
> > +          * bspec section 6.3.12.1 Zero-Width (Cosmetic) Line
> > +          * Rasterization.
> > +          */
> > +         line_width_u3_7 = 0;
> > +      }
> >        dw3 |= line_width_u3_7 << GEN6_SF_LINE_WIDTH_SHIFT;
> >     }
> >     if (ctx->Line.SmoothFlag) {
> >
> 
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