Problem with Cygwin/X from remote Linux

Problem with Cygwin/X from remote Linux

[Chris Carlson]

I've been using Cygwin on a Windows 7 laptop for a few years as an X
server from my Fedora Linux system.  I "ssh -X" to my Linux system and
run various X programs (thunderbird, chrome, nautilus, etc.) with very
few issues.

Every now and then, I will upgrade Cygwin_64 just to get the latest
changes.  I hope that the few issues I have will be cleared up.  I
believe the one issue I have with Thunderbird may be Thunderbird, not
Cygwin/X.

Anyway, over the past weekend, I upgraded again.  The upgrade seemed to
go well.  No surprises until...

One of the things I've been doing is learning OpenGL.  I'm converting a
sample program that I acquired while working at SGI to OpenGL (it was
written in gl, the original SGI graphics language). For the past few
months, all of my OpenGL programs have worked fine over the network.
Suddenly, with the latest version of Cygwin/X, it doesn't.

     Welcome to the XWin X Server
     Vendor: The Cygwin/X Project
     Release: 1.16.1.0
     OS: CYGWIN_NT-6.1 grover 1.7.32(0.274/5/3) 2014-08-13 23:06 x86_64
     OS: Windows 7 Service Pack 1 [Windows NT 6.1 build 7601] (Win64)
     Package: version 1.16.1-1 built 2014-09-29

     XWin was started with the following command line:

     X :0 -multiwindow

I discovered there are no visuals available to remote X connections that
support OpenGL double buffering.  There used to be, but no longer.
There are visuals available to direct connections, but not for remote.

I tried looking through the FAQ for answers, but I didn't see anything.
Is this something that has intentionally changed?  Where would I find it
if it is (for future reference so I don't bug you)?

Thanks,
Chris Carlson



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Re: Problem with Cygwin/X from remote Linux

[Jon TURNEY]

On 02/10/2014 04:53, Chris Carlson wrote:
> I've been using Cygwin on a Windows 7 laptop for a few years as an X
> server from my Fedora Linux system.  I "ssh -X" to my Linux system and
> run various X programs (thunderbird, chrome, nautilus, etc.) with very
> few issues.
>
[...]
>
>      Welcome to the XWin X Server
>      Vendor: The Cygwin/X Project
>      Release: 1.16.1.0
>      OS: CYGWIN_NT-6.1 grover 1.7.32(0.274/5/3) 2014-08-13 23:06 x86_64
>      OS: Windows 7 Service Pack 1 [Windows NT 6.1 build 7601] (Win64)
>      Package: version 1.16.1-1 built 2014-09-29
>
>      XWin was started with the following command line:
>
>      X :0 -multiwindow
>
> I discovered there are no visuals available to remote X connections that
> support OpenGL double buffering.  There used to be, but no longer.
> There are visuals available to direct connections, but not for remote.

Thanks for reporting this problem.  Unfortunately, I can't reproduce it.

Please can you attach the output of 'X -multiwindow -logverbose 3', so I 
can see what visuals the server thinks should be available, and the 
output of running 'glxinfo' on your remote system.

Can you give the version of Fedora you are using, and the version of the 
libGL package you have?

> I tried looking through the FAQ for answers, but I didn't see anything.
> Is this something that has intentionally changed?  Where would I find it
> if it is (for future reference so I don't bug you)?

No, this is not intentional.

I guess this is an unintended consequence of a change.  It would be 
useful in tracking down that change if you could identify the last X 
server release which worked correctly.

The release announce mails are a hopefully accurate summary of intended 
changes (e.g [1])

[1] https://cygwin.com/ml/cygwin-xfree-announce/2014-09/msg00004.html

-- 
Jon TURNEY
Volunteer Cygwin/X X Server maintainer

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Re: Problem with Cygwin/X from remote Linux

[Chris Carlson]

Hello, Jon.

The version of Fedora I'm running is:
Linux rolf 3.9.10-100.fc17.x86_64 #1 SMP Sun Jul 14 01:31:27 UTC 2013 
x86_64 x86_64 x86_64 GNU/Linux

I thought the two logs that you requested were a bit large for this 
e-mail, so I put them on my web site.  You can access them as:
http://beachware.org/Cygwin/glxinfo.cygwin
http://beachware.org/Cygwin/X.log

Believe it or not, I just so happen to have an XWin.0.log from my old, 
old, old version of Cygwin.  It was:

Welcome to the XWin X Server
Vendor: The Cygwin/X Project
Release: 1.15.1.0
OS: CYGWIN_NT-6.1 grover 1.7.30(0.272/5/3) 2014-05-23 10:36 x86_64
OS: Windows 7 Service Pack 1 [Windows NT 6.1 build 7601](Win64)
Package: version 1.15.1-2 built 2014-05-06

XWin was started with the following command line:

X :0 -multiwindow

Let me know if there's anything else I can provide.

Chris Carlson



On 10/2/2014 5:05 AM, Jon TURNEY wrote:
> On 02/10/2014 04:53, Chris Carlson wrote:
>> I've been using Cygwin on a Windows 7 laptop for a few years as an X
>> server from my Fedora Linux system.  I "ssh -X" to my Linux system and
>> run various X programs (thunderbird, chrome, nautilus, etc.) with very
>> few issues.
>>
> [...]
>>
>>      Welcome to the XWin X Server
>>      Vendor: The Cygwin/X Project
>>      Release: 1.16.1.0
>>      OS: CYGWIN_NT-6.1 grover 1.7.32(0.274/5/3) 2014-08-13 23:06 x86_64
>>      OS: Windows 7 Service Pack 1 [Windows NT 6.1 build 7601] (Win64)
>>      Package: version 1.16.1-1 built 2014-09-29
>>
>>      XWin was started with the following command line:
>>
>>      X :0 -multiwindow
>>
>> I discovered there are no visuals available to remote X connections that
>> support OpenGL double buffering.  There used to be, but no longer.
>> There are visuals available to direct connections, but not for remote.
>
> Thanks for reporting this problem.  Unfortunately, I can't reproduce it.
>
> Please can you attach the output of 'X -multiwindow -logverbose 3', so 
> I can see what visuals the server thinks should be available, and the 
> output of running 'glxinfo' on your remote system.
>
> Can you give the version of Fedora you are using, and the version of 
> the libGL package you have?
>
>> I tried looking through the FAQ for answers, but I didn't see anything.
>> Is this something that has intentionally changed?  Where would I find it
>> if it is (for future reference so I don't bug you)?
>
> No, this is not intentional.
>
> I guess this is an unintended consequence of a change.  It would be 
> useful in tracking down that change if you could identify the last X 
> server release which worked correctly.
>
> The release announce mails are a hopefully accurate summary of 
> intended changes (e.g [1])
>
> [1] https://cygwin.com/ml/cygwin-xfree-announce/2014-09/msg00004.html
>


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Re: Problem with Cygwin/X from remote Linux

[Jon TURNEY]

On 03/10/2014 05:19, Chris Carlson wrote:
>>> I discovered there are no visuals available to remote X connections that
>>> support OpenGL double buffering.  There used to be, but no longer.
[...]
> I thought the two logs that you requested were a bit large for this
> e-mail, so I put them on my web site.  You can access them as:

Thanks.

So, this is the set visuals that the X server supports.

> GL_VERSION:     3.1.0 - Build 8.15.10.2455
> GL_VENDOR:      Intel
> GL_RENDERER:    Intel(R) HD Graphics Family
[...]
> pxf vis  fb                      render         Ste                     aux    accum        MS    drawable             Group/
> idx  ID  ID VisualType Depth Lvl RGB CI DB Swap reo  R  G  B  A   Z  S  buf AR AG AB AA  bufs num  W P Pb  Float Trans Caveat
> -----------------------------------------------------------------------------------------------------------------------------
>   1  51  42 TrueColor    32   0   y   .  .       .   8  8  8  8   0  0   0   0  0  0  0    0    0  y . y     .     .     2
>   2  52  43 TrueColor    32   0   y   .  y xchg  .   8  8  8  8   0  0   0  16 16 16 16    0    0  y . y     .     .     2
>   3  53  44 TrueColor    32   0   y   .  .       .   8  8  8  8  24  8   0   0  0  0  0    0    0  y . y     .     .     2
>   4  21  45 TrueColor    32   0   y   .  y xchg  .   8  8  8  8  24  8   0  16 16 16 16    0    0  y . y     .     .     2
>   5  54  46 TrueColor    32   0   y   .  .       .   8  8  8  8  16  0   0   0  0  0  0    0    0  y . y     .     .     2
>   6  55  47 TrueColor    32   0   y   .  y xchg  .   8  8  8  8  16  0   0  16 16 16 16    0    0  y . y     .     .     2
>   7  56  48 TrueColor    32   0   y   .  y copy  .   8  8  8  8   0  0   0  16 16 16 16    0    0  y . y     .     .     2
>   8  57  49 TrueColor    32   0   y   .  y copy  .   8  8  8  8  16  0   0  16 16 16 16    0    0  y . y     .     .     2
>   9  41  4a TrueColor    32   0   y   .  y copy  .   8  8  8  8  24  8   0  16 16 16 16    0    0  y . y     .     .     2
>  10  58  4b TrueColor    32   0   y   .  .       .   8  8  8  8   0  0   0   0  0  0  0    1    4  y . y     .     .     2
>  11  59  4c TrueColor    32   0   y   .  y xchg  .   8  8  8  8   0  0   0  16 16 16 16    1    4  y . y     .     .     2
>  12  5a  4d TrueColor    32   0   y   .  .       .   8  8  8  8  16  0   0   0  0  0  0    1    4  y . y     .     .     2
>  13  5b  4e TrueColor    32   0   y   .  y xchg  .   8  8  8  8  16  0   0  16 16 16 16    1    4  y . y     .     .     2
>  14  5c  4f TrueColor    32   0   y   .  .       .   8  8  8  8  24  8   0   0  0  0  0    1    4  y . y     .     .     2
>  15  5d  50 TrueColor    32   0   y   .  y xchg  .   8  8  8  8  24  8   0  16 16 16 16    1    4  y . y     .     .     2

The mesa software renderer on the remote host constructs the set of 
visuals the client gets offered by picking the visuals from the server's 
set of visuals which match one of it's visuals

> OpenGL renderer string: Gallium 0.4 on llvmpipe (LLVM 0x300)
> OpenGL version string: 2.1 Mesa 8.0.4
[...]
>     visual  x   bf lv rg d st  colorbuffer  sr ax dp st accumbuffer  ms  cav
>   id dep cl sp  sz l  ci b ro  r  g  b  a F gb bf th cl  r  g  b  a ns b eat
> ----------------------------------------------------------------------------
> 0x051 24 tc  0  32  0 r  . .   8  8  8  8 .  .  0  0  0  0  0  0  0  0 0 None
> 0x053 24 tc  0  32  0 r  . .   8  8  8  8 .  .  0 24  8  0  0  0  0  0 0 None

Unfortunately this set is small, and indeed doesn't contain any 
double-buffered visuals.

Workarounds are to use either start Cygwin X server with -nowgl (so it 
too uses the software renderer and will offer a set of visual which is 
probably exactly the same), or to run the client with the 
LIBGL_ALWAYS_INDIRECT env var set (so that indirect rendering is used 
and the remote client has access to the actual set of visuals the server 
supports)

I think the real fix to this is to fix the remote libGL, either so it 
matches visuals less precisely, or so it offers more visuals which can 
match, but this is not simple.

> Believe it or not, I just so happen to have an XWin.0.log from my old,
> old, old version of Cygwin.  It was:
>
> Package: version 1.15.1-2 built 2014-05-06

Now I can reproduce this, it seems that this can be an unfortunate 
side-effect of the "Improve visual matching with a remote libGL by not 
reporting pbuffer size limits" change in 1.15.1-3 [1], which was 
intended to have the opposite effect, if previously no visuals at all 
were matching, so the software renderer was disabled, and we were 
falling back to indirect rendering.

[1] https://cygwin.com/ml/cygwin-xfree-announce/2014-06/msg00002.html

-- 
Jon TURNEY
Volunteer Cygwin/X X Server maintainer

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