[Mesa-dev] [PATCH] i965/gen8: Fix antialiased line rendering with width < 1.5

[Iago Toral]

On Thu, 2015-06-11 at 00:18 -0700, Kenneth Graunke wrote:
> On Thursday, June 11, 2015 09:03:37 AM Iago Toral Quiroga wrote:
> > The same fix Marius implemented for gen6 (commit a9b04d8a) and
> > gen7 (commit 24ecf37a).
> > ---
> >  src/mesa/drivers/dri/i965/gen8_sf_state.c | 22 ++++++++++++++++++++--
> >  1 file changed, 20 insertions(+), 2 deletions(-)
> > 
> > Ken, I don't have gen8 hardware available to test this so it would
> > be nice if someone else verifies that this fixes the piglit tests you
> > mentioned.
> 
> Oh, sorry - I was hoping we could include this in the helper function,
> since it's the exact same code for Gen6/7/8...

Ah right, you did mention that, sorry I forgot about it. I'll send a new
version shortly.

Iago

> > diff --git a/src/mesa/drivers/dri/i965/gen8_sf_state.c b/src/mesa/drivers/dri/i965/gen8_sf_state.c
> > index 83ef62b..22c1c4a 100644
> > --- a/src/mesa/drivers/dri/i965/gen8_sf_state.c
> > +++ b/src/mesa/drivers/dri/i965/gen8_sf_state.c
> > @@ -156,8 +156,26 @@ upload_sf(struct brw_context *brw)
> >     /* _NEW_LINE */
> >     float line_width = brw_get_line_width(brw);
> >     uint32_t line_width_u3_7 = U_FIXED(line_width, 7);
> > -   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 < 1.5) {
> > +      /* For 1 pixel line thickness or less, 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;
> > +   }
> > +
> >     if (brw->gen >= 9 || brw->is_cherryview) {
> >        dw1 |= line_width_u3_7 << GEN9_SF_LINE_WIDTH_SHIFT;
> >     } else {
> >