xf86-video-intel: unexpected phenomenon on XV texture adapter with no scaling

[Jacques, Hugo]

Guys, I entered a defect in the Bugzilla regarding that issue.

https://bugs.freedesktop.org/show_bug.cgi?id=22370 

Maybe you want to add there too the information you have and the findings you make.

Regards,

Hugo

> -----Original Message-----
> From: Roland Scheidegger [mailto:sroland at tungstengraphics.com]
> Sent: Friday, June 19, 2009 20:12
> To: Krzysztof Halasa
> Cc: Jacques, Hugo; xorg at lists.freedesktop.org
> Subject: Re: xf86-video-intel: unexpected phenomenon on XV texture adapter
> with no scaling
> 
> On 20.06.2009 00:04, Krzysztof Halasa wrote:
> > Hi,
> >
> > "Jacques, Hugo" <Hugo.Jacques at verint.com> writes:
> >
> >> I get a strange phenomenon using the XV texture adapter in YV12 format
> >> on my 945G hardware and a 2.7.0 xf86-video-intel driver.
> >>
> >> I fill a rectangle with many 1 pixel-high horizontal lines. Odd lines
> >> are black and even lines are white.  I send this rectangle using
> >> XVShmPutImage to a window with the same size so that no scaling
> >> occurs.
> >>
> >> I would expect to see the black/white horizontal lines pattern. But I
> >> get a uniformly grey rectangle!
> >
> > I think we're then in some sort of Matrix. I just opened the xorg list
> > folder to write about precisely the same observation :-)
> >
> >> Same phenomenon appears on either VGA,
> >> DVI or CVBS-TV monitors: it doesn't seem to be monitor/video encoder
> >> issue-related.
> >
> > Yes. BTW the data in video memory is already "corrupted" - tested with
> > mplayer, playdv for simplicity, and verified with xwd.
> >
> > The same on i915 + git driver and on Radeon RV6xx with Fedora 11. The
> > effects are precisely the same, there is some averaging/filtering here.
> > But it only happens with Xvideo output - X11 and GL are fine. OTOH on
> > R300 it's different - textured XVideo output looks good (at least much
> > better, that's a high res display and individual pixels are hard to
> > see), but the XVideo overlay has the symptom (RV6xx has no overlay).
> 
> X11 doesn't do any scaling, so you will always get a 1:1 exact mapping.
> textured xv however uses bilinear texture filtering (some drivers can
> actually do better), it doesn't even know what a 1:1 mapping is. So if
> you have some half-pixel offset somewhere bilinear filter will produce
> exactly the same grey for all pixels if you have an alternating pattern
> of black and white lines in the source image.
> With a very quick look at the r600 code, I suggest trying out the
> attached patch to test my theory about half pixel offsets in hardware.
> This could mess though with EXA acceleration, so if you see a bit odd
> corruption don't be surprised :-).
> As said I'm not sure if (and if how) i915 can be tweaked for that (if
> not just add offset to the tex coords).
> Overlays are a bit a different matter, not only are they usually hard to
> set up really correctly but they may actually use filters where you
> can't get a basically unfiltered output even with a 1:1 mapping (not
> sure about this though), unless you'd switch filtering off (I guess
> could do that if we'd add detection for unscaled case).
> 
> Roland
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