Using 8 bit Web on Linux

1. INSTALLATION

   The following assumes that you have loaded and installed installed Web as described in: Web: Installation on GNU/Linux

Web_linux uses a 8 bit pseudo-color visual. With some graphics drivers, on some GNU/Linux distributions, there is a problem running 8 bit pseudo-color visuals when the workstation's visual depth is set to 24 bits. Some implementations do not even provide a 8 bit pseudo-color display in their default X configuration file. There here are three ways to get 8 bit Web to run. First ensure that you have an 8 bit "Display" available:

If the file: /etc/X11/XF86Config/xorg.conf or /etc/X11/xorg.conf (location depends on your Linux distribution) lacks a SubSection "Display" with depth: 8 then you will have to add such a SubSection.

Add words in red italics under: Section "Screen" (Your monitor may not be capable of all these size modes. If not, delete the offending size mode(s)).

SubSection "Display"

Depth 8 Modes "1920x1200" "1900x1200" 1600x1200" "1400x1050" "1280x1024" "1280x960" "1152x864" "1024x768" "800x600" "640x480"

EndSubSection

Now that you have ensured the availibility of the necessary display depth you can use one of the following methods.

1. Switch your default display depth to 8 bits.

   E.g. if you are using SUSE
   

   'Start up YAST' --
   'Under: Hardware' --
   'Under: Graphics Card & Monitor' --
   'Change colors to 256 (8 bits)'
   You may have to login as root to do this.

This will mean that applications which require a 24 bit depth will not be usable. If you do not wish to change your default display to 8 bits you can try one of the following methods.

2. Create additional X server at 8 bits

   Create two X servers running in different virtual consoles switched with the F7 and F8 Function keys:
   

   <Ctrl-Alt-F7> Default depth display

   <Crtl-Alt-F8> 8 bit display

   Most GNU/Linux istallations start several virtual consoles which are accessible by pressing <Ctrl-Alt-F1>, .. <Ctrl-Alt-F*> while you are running inside your Window Manager. Normally <Ctrl-Alt-F8> lacks any connection to a Terminal or an X Server and can be used for an additional X session.

   In a regular xterm window start an additional X server, this one in 8 bit mode, using the following command:
   startx -- : 1 -depth 8 vt8 &2>/dev/null &
   This will bring up a new session on display: 1 with depth:8 where you can start: web_linux.

   You can now switch back and forth between the two X servers using <Ctrl-Alt-F7> (original Truecolor X server on :0) and <Ctrl-Alt-F8> (8 bit Pseudocolor X server on :1).

   NOTE: Some older Nvidia graphics drivers may corrupt display or lock up the system (requiring rebooting) when quickly switching consoles, so this method may not work on such systems.
   

3. Use vnc (Virtual Network Computing) to create a virtual display.

   Most GNU/Linux distributions include vnc in their default installation which can be used to create a virtual display in a window on your current desktop.
   When vnc is installed:

   vncserver -cc 3 -depth 8
   Provide a password if prompted.
   

   Returns "New 'X' desktop is hostname:number"
   e.g.: "New 'X' desktop is green:1"
   

   vcnviewer :1
   Provide a password if prompted.
   

   Opens new desktop within a window
   Here you can start web_linux normally or you can start it automatically by editing your vnc viewer startup file: ~/.vnc/xstartup

   vncserver -kill :1
   Kills the vnc server.
   

4. Testing Web.

   Use your web command to start Web.

   If Web runs and but the other windows on the screen have strange colors when the Web window is in use (has focus).

   • This is expected.

     Web installs its own colormap so that it can use private colormaps for intensity display. This is an old (and powerfull) technique for visualization which is disappearing these days but still exists in Web.




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Source: web8onlinux.html     Updated: 30 Oct. 2007     ArDean Leith