Ideas for X improvement.

Pat Kane pekane52 at
Thu May 26 05:34:41 PDT 2011

I like VNC and have built both loadable module and DDX version.

The main problem with the DDX version is that since VNC
has a GPL  license I can not merge the code into my Xorg
source tree.


On Wed, May 25, 2011 at 6:07 PM, David Jackson <djackson452 at> wrote:
> On Wed, May 25, 2011 at 4:36 PM, Glynn Clements <glynn at>
> wrote:
>> David Jackson wrote:
>> > A display driver that contains a VNC server. The problem with x11vnc is
>> > that
>> > it is slow, very slow. XVnc server, which is a X server that contains a
>> > VNC
>> > server but has no hardware drivers, is much faster since the VNC server
>> > is
>> > built directly into the X server,
>> What sample size does your analysis use? How many different hardware
>> configurations, and how many different applications?
>> x11vnc has the drawback that it's reading a framebuffer which is
>> typically in video memory, so the data has to be read over the bus.
>> The speed of this operation may vary significantly depending upon the
>> hardware being used. It may also vary depending upon the amount of
>> activity (i.e. if it has to wait for the outstanding rendering
>> operations to complete before it's allowed to read the framebuffer).
>> Xvnc has the advantage that the framebuffer is in system memory. But
>> this is also a drawback, as it means that all rendering is performed
>> in software. Try running an application which uses OpenGL to render
>> detailed scenes; you might want to reconsider your assertion about
>> Xvnc is fast.
>> IOW, it's a case of "choose your poison". x11vnc has fast rendering
>> but slow export, Xvnc has slow rendering but fast export. A similar
>> tradeoff exists for X11 verus VNC for remote display.
>> > however this does not allow one to export
>> > their main X display which is also displayed directly to video hardware.
>> > The
>> > solution here is to include a driver in the main server
>> > distribution
>> > for a VNC server that can be loaded into the X server. The VNC server
>> > driver
>> > should be able to be dynamically loaded while the server is running and
>> > the
>> > output of the server displayed simultaneously to VNC clients and to the
>> > local video hardware. This can be controlled from provided command line
>> > and
>> > GUI utilities.
>> Does the VNC driver read the framebuffer on the video card (which
>> suffers from the same performance issues as x11vnc), or does it
>> attempt to duplicate the framebuffer by emulating whatever video
>> hardware is installed? If it's the latter, the application will be
>> slowed to the speed of the VNC driver's software renderer (which will
>> be extremely complex, as it will have to mimic every feature which is
>> available in at least one hardware driver).
>> > One of the very severe problems I have been having is that Xvnc does not
>> > support Render extensions, and many applications no longer work without
>> > the
>> > Render extension. VNC driver with therefore must support the
>> > Render
>> > extension and other ones.
>> The main "other one" being OpenGL, for which a software implementation
>> will be much, much slower than a modern GPU.
>> > Dynamic runtime enabling and disabling, configuration and setup and
>> > removal
>> > of display output and input drivers while the server runs without server
>> > restart. this allows for instance, the user to have the X server display
>> > to
>> > a new target while the server runs, or display to many different display
>> > outputs at the same time This includes the VNC Server driver above, this
>> > allows a person to easily swtich the VNC on and off from displaying to
>> > certain outputs, such as they could turn off display to the local
>> > monitor
>> > and then turn it back on again, or turn on and off VNC display.
>> >
>> > Another feature that increases flexibility to the user would be to allow
>> > the
>> > user to direct display of a certain window or the entire root window and
>> > display over an X client connection to another server, or any number of
>> > other servers. This would also forward the windows children who would
>> > also
>> > be displayed on the remote server inside the parent window.
>> To do this at the protocol level requires a completely new protocol
>> and significant support from the toolkit. The X protocol exposes a
>> significant amount of implementation detail to the client. Much of
>> that information is required to remain constant for the lifetime of
>> the client.
>> E.g. if the client queries the list of OpenGL extensions, and starts
>> using some of them, there's no mechanism by which to inform the client
>> that an extension is suddenly unavailable, which would be required if
>> you were to "redirect" the window to a different server with different
>> hardware.
>> Even if such a mechanism existed, it's debatable how many applications
>> would support it. Reconstructing the current server-side state from
>> scratch is a lot of work, and toolkits can't always help (e.g. they
>> won't help reconstruct the server-side OpenGL state, as the toolkit
>> doesn't get involved in the rendering process).
>> > Many users, including myself, want to have many X servers running at the
>> > same time and then at run time be able to change to where these servers
>> > are
>> > being displayed, and as well when an app is started, to which server it
>> > is
>> > displayed with the -display option.
>> AFAICT, there are only two feasible approaches to window "mobility":
>> 1. VNC-like framebuffer sharing. The application connects to a
>> specific X server which performs all rendering. You have the option to
>> forward rendered images to other systems for physical display.
>> 2. Use GUI toolkits which offer an abstract, high-level interface to
>> the client. The toolkit has the ability reconstruct and clone windows
>> at will.
>> --
>> Glynn Clements <glynn at>
>> _______________________________________________
>> xorg at X.Org support
>> Archives:
>> Info:
>> Your subscription address: djackson452 at
> x11vnc is noticeably slower. I think the really annoying thing that makes it
> hard to use is that there is a longer delay when typing for characters to
> display on the screen than there is with Xvnc. I can notice this. When you
> are typing characters do display much more quickly to the screen on Xvnc.
> That is a big issue, because, it is really hard to type when you have a long
> delay of characters appearing when you type them.Perhaps this is due the
> polling of the framebuffer.
> The VNC driver could  do its own rendering, get the graphics commands from
> the application directly. Yes, you are correct that is slow for many complex
> operations. You are correct, the other alternative is to grab the
> framebuffer. You are correct it might be faster for those complex graphics.
> Grabbing the framebuffer inside the X server and feeding it out to VNC
> clients via a VNC server in the X server, might save a little bit of time by
> avoiding having to be sent over a socket to another process, but i do not
> know if that is true. It may be it might do all that being interrupted fewer
> or no times, where with x11vnc you are gauranteed a task switch and some
> time for x11vnc to get the CPU. I guess x11vnc asks for the framebuffer over
> an X connection, then wait for the X server to get the CPU to process the
> request, then wait again for x11vnc to get CPU and the data to be sent to
> VNC clients. if we have a framebuffer based VNC driver inside the X server,
> it may allow for tighter synchronisation and less delay. I cannot say how
> significant it would be.
> The other issue mentioned, about the window forward feature. You are
> correct. I have been thinking about these issues. It would be best for it to
> be invisible to clients. Ive been thinking about these problems.
> I am know C, however I know little about X internals or X protocol. Is there
> a good source of documentation that would give a person a full introduction
> and overview of how the X server works,including how it all fits together,
> and a tour of the system and documentation of the internals such as
> functions, variables etc? Basically everything need for a person who only
> knows C to learn all about how the X server works?
> _______________________________________________
> xorg at X.Org support
> Archives:
> Info:
> Your subscription address: pekane52 at

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