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Intel SNA vs. UXA On Ivy Bridge (July 2012)

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  • #16
    Well SNA enabled triggers more often the xserver crash with debian wheezy when kde 4 effects are turned off/on. As i still need that to get teerfree video i would like to know what patches are needed for the xserver - best force em to be added to the debian wheezy xserver...

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    • #17
      Originally posted by ickle View Post
      Well, I've obviously completedly failed if you haven't noticed any of your common tasks improved by SNA. So what is your common workload?
      Maybe I'm just bad at noticing these things

      Generally on this laptop I don't do anything too heavy, web browsing, videos, music, text editing.

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      • #18
        Ok, I definitely notice firefox seems a lot snappier with sna enabled

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        • #19
          So for the first time after a long while, I used my Ironlake machine full-time today. And I had this weird feeling all the time as if the display is out of focus. In trying to figure it out, I switched from SNA back to UXA. And what do you know, the feeling was gone immediately. So I took some screenshots.

          Here a toolbar button with UXA:

          The same toolbar button with SNA:


          Note in particular the right edge. You might think that the difference is very small, but it's enough to give me the weird feeling.

          Versions of relevant packages are xf86-video-intel-2.20.3, cairo-1.12.2, gtk2-2.24.11, the theme being rendered is Clearlooks. Such a tiny thing, but you know what, I'll stick with UXA for the time being. I'm very sensitive to such things. For example, I use the lcdlegacy freetype filter for fonts, because what the lcddefault filter renders is way too blurry for my eyes.

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          • #20
            Originally posted by Gusar View Post
            So for the first time after a long while, I used my Ironlake machine full-time today. And I had this weird feeling all the time as if the display is out of focus. In trying to figure it out, I switched from SNA back to UXA. And what do you know, the feeling was gone immediately. So I took some screenshots.

            Here a toolbar button with UXA:

            The same toolbar button with SNA:


            Note in particular the right edge. You might think that the difference is very small, but it's enough to give me the weird feeling.

            Versions of relevant packages are xf86-video-intel-2.20.3, cairo-1.12.2, gtk2-2.24.11, the theme being rendered is Clearlooks. Such a tiny thing, but you know what, I'll stick with UXA for the time being. I'm very sensitive to such things. For example, I use the lcdlegacy freetype filter for fonts, because what the lcddefault filter renders is way too blurry for my eyes.
            That turns out to be a bug in cairo...

            commit e41dffb329e4a6fcb4e75fb501843838a499c4c8
            Author: Chris Wilson <chris@chris-wilson.co.uk>
            Date: Mon May 14 17:46:32 2012 +0100

            stroke: Don't drop clockwise==0 lines

            If the join indicates the pair of edges are parallel, we may be
            considering the final segment of the spline with a different tangent
            vector than the slope of the final edge and so lead to false dropping of
            an edge. This has the effect that the line segments between 'arc arc arc
            arc' (a rounded rectangle) are no longer horizontal or vertical. As path
            construction tries to eliminate joins between colinear segments, this
            optimisation should not be required anyway.

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            • #21
              Originally posted by ickle View Post
              That turns out to be a bug in cairo...
              Thanks for that. I recompiled 1.12.2 with the fix, then switched back to SNA. Now I got something different from both previous ones



              Looks sharp though, so I'll stick with it.

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              • #22
                Originally posted by Gusar View Post
                Thanks for that. I recompiled 1.12.2 with the fix, then switched back to SNA. Now I got something different from both previous ones



                Looks sharp though, so I'll stick with it.
                Cairo asks for Imprecise rendering by default, so the driver is allowed to take a few shortcuts and avoid the overhead of enforcing an 15x17 sampling grid for trapezoidal rasterisation, but still has to obey various rules to ensure that rendering a set of trapezoids is still deterministic. Hopefully I have chosen a good compromise between speed and quality, it should still be higher quality than using skia for example ;-)

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