Remote graphics over network

Harry123

Perhaps I'm looking at it too simplistically, but it seems to me that a graphical shell is not required to generate pure pixels in the program's memory. Qt has most of the required software, and if it may rely for some graphical operations on the operating system, existing open-source libraries can surely substitute.
Whatever graphical information Qt may require, such as screen size and resolution, can be communicated by the graphical client from its own environment.
Certainly some adjustments may be required in the core libraries of Qt, which is why I believe a more knowledgeable developer than myself is required.

@SGaist

VNC presents the desktop, while a Docker Windows container does not have a desktop. It may only have consoles, either Cmd or PowerShell. You may liken the Windows Server under Docker to a Linux server without X.

SGaist

I didn't talk about running a VNC server in a Windows docker.

I am talking about the Qt VNC backend which lets you connect a VNC client to your application to visualise its content.

Harry123

@SGaist

I don't understand - if the app is running in the Docker container, there's no graphical surface to visualize, or at least not one created by Windows. I don't think that VNC creates its own canvas, or otherwise it could support multiple sessions, while currently it only mirrors the desktop created by Windows.

SGaist

As I already wrote: not the VNC application. VNC doesn't require a physical display.

Harry123

@SGaist

I wasn't aware of VNC for headless servers, so I did some research.
For generic VNC, it seems like all the success stories were on Linux, and in addition required at least a display adapter and its installed driver, even if having no monitor.

For Qt, I have found The VNC Protocol and Qt for Embedded Linux which isn't helpful and anyway for Qt 4.8.
I have found references to the QVNCServer class, but none with doc later than Qt 4.8 and no file by that name in the sources of Qt 5.
But even if QVNCServer is no longer supported, this means that the project is easier than I thought.

Could you point me to any article for using Qt VNC on a Windows totally headless server using Qt of any version ?

Harry123

I have advanced some more and found VNC in Qt 5.9, but must say that there is almost no documentation and no samples.

Can anyone help ?

SGaist

No I don't have such an article at hand.

As for testing the VNC backend:

Download the Qt sources matching your version
Build the VNC platform plugin
Install it
Pass -platform vncas parameter of your application

Harry123

@SGaist

Isn't the VNC platform plugin an integral part of the distribution ?

I can find no documentation later than Qt 4.8, and that also is scarce.
The VNC code for Qt 5.10 is much more voluminous than that of 4.8 and is a total rewrite, but no documentation.

SGaist

It's back since 5.9 IIRC.

QPA Parameters:

port by default 5900
size=WidthxHeight logical size
mmsize=WidthxHeight physical size
depth (8, 16, 32)

All are optional.

Harry123

@SGaist

Thanks for the info.
I marked this as solved, although I'm not really too confident about using this very new software.
If only bug reports were better supported (of 3 bug reports none ever got solved).

SGaist

Which reports ?

Harry123

@SGaist

4 bug reports in order of nuisance:

QTBUG-60576
QTBUG-54119 (wrongly marked as solved)
QTBUG-53119
QTBUG-51624

SGaist

They don't seem to be related to the VNC plugin itself.

Harry123

@SGaist

No, but I'm not sure I will start with the new VNC software, being basically beta tester, without direct contact with the developer.
The bug report site does not inspire me with confidence.
I have launched a query on the Interest forum, and am still waiting for anyone to answer.