Re: [ferret_users] Running ferret on a Linux machine through a VNC server

Hi Ned,

I cannot say whether this is a Chicken of the VNC problem or a Ferret problem, but it is clearly a problem of the interactions between the two. The way that the Ferret command, FRAME/FORMAT=GIF, works is that Ferret (running on the host machine -- the "X client") asks the X-windows display server (the machine displaying the graphic) to please (it always says "please") send back a pixmap of the color indices. That is the process that is hanging for you.

Thinking out loud ...
When you are running Chicken of the VNC, Ferret and X both "think" they are running locally on your Redhat Linux machine. Yet the conversation between X server and X client -- something that works on the Redhat display screen -- is not working through the C.o.t.VNC connection. In order for it to work, CotVNC has to have logic in itself that allows it to send back a pixmap. Easy to imagine that particular code logic may be untested/faulty/non-existent in CotVNC, as it would rarely be used.

Assuming that this is NOT a bug in CotVNC, an area to look at (based upon past problems we have experienced with FRAME/FORMAT=GIF) is the configuration of the color model. For example, how does CotVNC cope if the Linux display were set to 16 bit indexed color, whereas the Mac were set to TrueColor? The FRAME/FORMAT=GIF command can work with indexed color, but not with TrueColor. (Maybe X hangs when a TrueColor X server is asked to give back an indexed color map ... I don't recall.) I would suggest trying experimentally playing with combinations of color configuration settings between, Redhat/Linux, CotVNC and Mac. It is understandably messy, since 3 different color model configurations may effect the results. (Kevin is familiar with the Linux configuration of the X color model.)

sorry I cant be more specific - Steve

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E. D. (Ned) Cokelet wrote:

Background: On land I run ferret on a networked Linux computer running the Red Hat operating system, but I do it through X-windows on my networked Macintosh. I open one or more X-windows on my Mac, and run ferret within those with no problems. I can produce plots and make gifs of them using the FRAME/FORMAT=GIF command.

Our group also goes to sea. There I am often the only user of the Linux computer, and I sit at its console running ferret within an X-window within the Red Hat GUI. That GUI has some nice graphical tools that I can take advantage of.

Back on land, it has been pointed out to me that I could have the "look and feel" of the Red Hat GUI on my Mac if I run a VNC (virtual network computer) server on the networked Linux machine and a VNC client on the Mac. I downloaded "Chicken of the VNC" - the favored, free, Mac VNC client to my Mac - and it really does work. It's just like sitting at the Linux console with all the Red Hat GUI tools available. I can open X-windows there and run ferret. BUT there is a problem. The ferret graphical display window looks the same as ever, but I cannot capture the graphic with the FRAME/FORMAT=GIF command. Ferret just hangs without responding.

Questions: Has anyone captured a graphic as a gif successfully with a VNC client? On a Mac or any other machine? Is the problem that ferret cannot capture a gif through a VNC? If so, can that be worked around? Or is it a Mac problem? Or is it a Chicken of the VNC problem?

P.S. We thought it might be a backing store issue, and we've installed the latest VNC server on Red Hat. It supports X-window backing store. When I overlap a ferret graphics window with a text window and then uncover it again, the graphics window repaints, so backing store seems to be working.

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Edward D. (Ned) Cokelet, Ph.D. Oceanographer

NOAA/PMEL off: (206) 526-6820

7600 Sand Point Way NE fax: (206) 526-6485

Seattle, WA 98115-6349

Edward.D.Cokelet@xxxxxxxx

The contents of this message are mine personally and do not necessarily reflect any position of the Government or the National Oceanic and Atmospheric Administration.

-- 
Steve Hankin, NOAA/PMEL -- Steven.C.Hankin@xxxxxxxx
7600 Sand Point Way NE, Seattle, WA 98115-0070
ph. (206) 526-6080, FAX (206) 526-6744

"The only thing necessary for the triumph of evil is for good men
to do nothing." -- Edmund Burke