[PATCH renderproto] Add floating point transforms

[Siarhei Siamashka]

On Tue, 19 Aug 2014 10:50:08 +0600
"Alexander E. Patrakov" <patrakov at gmail.com> wrote:

> 19.08.2014 03:02, Keith Packard wrote:
> > Siarhei Siamashka <siarhei.siamashka at gmail.com> writes:
> >
> >> Do you have a reproducible testcase for this problem? Being off by
> >> several pixels seems to be very wrong. Especially if this happens
> >> often.
> >
> > Non-affine transforms cause problems. I noticed this with RandR when
> > doing keystone correction.
> >
> > Here's a simple example:
> >
> > Desired matrix:
> >
> >   33.13915858	15.17037037	-16384.00000000
> >   0.00000000	23.73634938	0.00000000
> >   -0.00057170	-0.00182142	25.70348287
> >
> > Rounded to 16.16 fixed matrix:
> >
> >   33.13916016	15.17036438	-16384.00000000
> >   0.00000000	23.73634338	0.00000000
> >   -0.00056458	-0.00181580	25.70347595
> >
> > Actual bits:
> >
> >   { 0x00014dba, 0x000098c6, 0xfd7b7d45 },
> >   { 0x00000000, 0x0000ef09, 0x00000000 },
> >   { 0xffffffff, 0xfffffffb, 0x000102d9 },
> >
> > Take the point 2560,1600 and transform:
> >
> > desired:        4348.04, 1780.87
> > actual:         4342.50, 1778.60
> >
> > error:          5.99
> 
> Sorry, but I think that we have bigger problems. Please look at 
> https://bugs.freedesktop.org/show_bug.cgi?id=39949 (which was a blocker 
> for xserver-1.12 and makes mouse input on scaled displays unusable in 
> some cases). Since there was no manpower to review that bug for years, I 
> think that the best course for now is to prohibit all transforms that do 
> not amount to mere translation. You can change my opinion by reviewing 
> the patch in the bug.

Alexander, input handling is a different problem, which is not directly
related to the transform accuracy. But thanks for bringing it up.

Also I got an off-list e-mail about xrandr from another person. Which
clearly shows that there is some interest in it, but people might be
a little bit too shy to complain or remind about problems in public :-)

-- 
Best regards,
Siarhei Siamashka