Pseudo colour displays

As I mentioned in section  you can use VNC as another way around the problems with Pseudocolor applications on Truecolor displays. Effectively you use VNC to display a self-contained 8-bit Pseudocolor X display on your desktop, programs which require such a display will then run happily in that window, and colour hungry applications which can run in True color can run outside it.

With VNC installed on your system, and the binaries in your PATH, to start a Pseudocolor window on any X display you must first start a VNC server using:

% vncserver -cc 3 -depth 8

        New 'X' desktop is mypc:1

        Starting applications specified in /home/aa/.vnc/xstartup
        Log file is /home/aa/.vnc/X.log

The first time you do this, you will be asked for a password for protecting your VNC sessions. This can be the same or different from the password you use for logging in on that computer. Choose it in the same way as you would a normal Unix password.

You must then start a VNC viewer using the display numebr reported by the preceeding command:

% vncviewer :1
        vncviewer: VNC server supports protocol version 3.3 (viewer 3.3)
        Password:

At this point type in the password you gave when you first ran vncserver. A window will now pop up on your screen, this is a new X Windows desktop. Run Starlink programs from xterms in that window, and they will pop up as sub-windows in that window and run without problem. Outside that window, the X display will carry on working as normal.

When you have finished with the pseudocolour desktop, close down the windows as in a normal X session and terminate the server, using the display number again:

% vncserver -kill :1

Figure: VNC displaying a pseudo colour desktop on a true colour display.

Figure  illustrates several aspects of the VNC system. Here we show a Pseudocolor VNC X Windows desktop (1024$\times$768 pixels) running the twm window manager on a DEC Alpha using KAPPA to display a CCD image. The VNC desktop is being displayed ontop of a True colour X Windows desktop (1280$\times$1024 pixels) running the WindowMaker window manager on a Linux PC.

You can customise the size of the pop up desktop by using the command line option -geometry, e.g.

% vncserver -cc 3 -depth 8 -geometry 1024x768
        New 'X' desktop is mypc:1

        Starting applications specified in /home/aa/.vnc/xstartup
        Log file is /home/aa/.vnc/X.log

While the applications automatically started along with the vncserver can be customised from the $\sim$/.vnc/xstartup script (created the first time vncserver is run) in your home directory. By default this script starts one xterm and the twm window manager. By editing $\sim$/.vnc/xstartup this behaviour can be modified; by copying or symbolically linking your .xsession or .xinitrc to it the VNC window can be given the same behaviour as your normal X session.

Additionally, it is not necessary to kill the VNC server at the end of a session, or indeed ever; the only important thing is not to leave an ever increasing number of unused servers running on the system. If it's more convenient, you can simply close the VNC viewer window at the end of a session, and next time you wish to use it start vncviewer again, without having to rerun vncserver, and your desktop will be exactly as you left it.