pixel format is out of sync, after refreshing and suddenly changing pixel format

[Anon Sricharoenchai]

This problem doesn't exist in VNC non-free edition?

On 12/12/07, James Weatherall <jnw "at" realvnc.com> wrote:
> Hi Anon,
>
> This is a know limitation of the Refresh Screen option in VNC Free Edition &
> VNC Free Edition-based software, which isn't "safe" to use if the VNC Viewer
> might be changing pixel format at a later point.  You shouldn't need to use
> Refresh Screen, in general.
>
> Cheers,
>
> --
> Wez @ RealVNC Ltd
>
>
> > -----Original Message-----
> > From: vnc-list-admin "at" realvnc.com
> > [mailto:vnc-list-admin "at" realvnc.com] On Behalf Of Anon Sricharoenchai
> > Sent: 12 December 2007 12:25
> > To: vnc-list "at" realvnc.com;
> > vnc-tight-devel "at" lists.sourceforge.net; anon.hui "at" gmail.com
> > Subject: pixel format is out of sync, after refreshing and
> > suddenly changing pixel format
> >
> > Hi,
> >
> > I'm not sure to call this a bug in vncviewer, or a bug in VNC
> > protocol.
> >
> > Anyhow, this bug apply to realvnc 4.0 to 4.1.1.  The bug may
> > demonstrate the flaw in VNC protocol, which don't have any
> > mechanism to ensure the synchronization of the pixel format
> > between client and server.
> >
> > Let's see how to reproduce this bug first, and then see how
> > pixel format is out of sync.
> > (To view this bug in a clear formatted text, visit
> > http://opensource.wikia.com/wiki/Bugs:realvnc4/pixel_format_is
> > _unpredictable_after_refreshing_and_suddenly_changing_pixel_format
> > )
> >
> > == How to reproduce ==
> > Run the following command in some terminal, "terminal1", in
> > this example,
> >
> >    terminal1 $ Xvnc :1 -nolisten tcp -auth /dev/null
> > -localhost -SecurityTypes=None -geometry 800x600 -depth 24 &
> >    terminal1 $ DISPLAY=:1 xterm -e perl -e '$|=1;
> > for(;;){print"."; select(undef,undef,undef,0.001); }' &
> >
> > Then open another terminal, "terminal2", run vncviewer,
> >
> >    terminal2 $ vncviewer :1 -shared -AutoSelect=0 -ViewOnly=1
> > -FullColor
> >
> >    VNC Viewer Free Edition 4.1.1 for X - built Jan  6 2007 00:46:26
> >    Copyright (C) 2002-2005 RealVNC Ltd.
> >    See http://www.realvnc.com for information on VNC.
> >
> >    Fri Dec  7 20:11:20 2007
> >     CConn:       connected to host localhost port 5901
> >
> >    Fri Dec  7 20:11:21 2007
> >     CConnection: Server supports RFB protocol version 3.8
> >     CConnection: Using RFB protocol version 3.8
> >     TXImage:     Using default colormap and visual,
> > TrueColor, depth 24.
> >     CConn:       Using pixel format depth 24 (32bpp)
> > little-endian rgb888
> >     CConn:       Using ZRLE encoding
> >
> > Switch back to "terminal1", suspend the Xvnc,
> >
> >    terminal1 $ killall -TSTP Xvnc
> >
> > Then switch to vncviewer x11 window, refresh screen, and
> > change colour level,
> >
> >    vncviewer x11: press F8 --> select "Refresh screen"
> >    vncviewer x11: press F8 --> select "Options..." --> select
> > "Very low (8 colours)" in "Encoding and Colour Level:" --> click "Ok"
> >
> > Switch to "terminal1", resume Xvnc,
> >
> >    terminal1 $ killall -CONT Xvnc
> >
> > vncviewer will then fail like this,
> >
> >    terminal2 $ vncviewer :1 -shared -AutoSelect=0 -ViewOnly=1
> > -FullColor
> >    <--cut-->
> >    ...
> >    <--cut-->
> >     CConn:       Using ZRLE encoding
> >
> >    Fri Dec  7 20:11:45 2007
> >     CConn:       Using pixel format depth 3 (8bpp) rgb111
> >    vncviewer: ../rfb/zrleDecode.h:196: void
> > rfb::zrleDecode8(const rfb::Rect&, rdr::InStream*,
> > rdr::ZlibInStream*, rdr::U8*,
> > rfb::CMsgHandler*): Assertion `len <= end - ptr' failed.
> >    Aborted
> >
> >
> >
> > == Cause ==
> > This is because the client and server fail to synchronize the
> > pixel format, which is depicted as follow,
> >
> >                              server send FramebufferUpdate0
> >                              server is suspended
> >    client receive FramebufferUpdate0
> >    client send FramebufferUpdateRequest1:incremental=true
> >
> >    user request refresh screen
> >    client send FramebufferUpdateRequest2:incremental=false
> >    user change colour level
> >
> >                              server is resumed
> >                              server receive
> > FramebufferUpdateRequest1:incremental=true
> >                              server send FramebufferUpdate1
> >    client receive FramebufferUpdate1
> >    client change its internal pixel format to new pixel format
> >    client send SetPixelFormat
> >    client send FramebufferUpdateRequest3:incremental=false
> >               (non-incremental since pixel format changed)
> >    client is now expecting new pixel format from server
> >                              server receive
> > FramebufferUpdateRequest2:incremental=false
> >                              server send FramebufferUpdate2
> > with old pixel format
> >    client receive FramebufferUpdate2 with old pixel format
> >    client interprete FramebufferUpdate2 as new pixel format
> >    client mis-interprete pixel format, and then fail
> > _______________________________________________
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> >
>
>