[To reply replace "Aaron.Sloman.XX" with "A.Sloman"]
On
> Date: 10 Dec 1999 00:55:03 GMT
I wrote about problems under linux (with a DEL laptop) using
> the version of David Young's popvision
> library available at the free poplog site
>
> http://www.cs.bham.ac.uk/research/poplog/popvision.tar.gz
> ...
> ... , rci_show and rc_array do not work when I use the laptop
> screen locally
> ...
> In both cases the mishap is 'Unable to allocate colour map entries'
> in the lconstant procedure getcrange.
>
> Looking at the code suggests that XpwAllocColorRange is not working
> (i.e. it always returns a false result),
I conjectured that this had something to do with the fact that
whereas lib popvision worked fine on an 8bit Sun colour display the
PC had more bits (I think it's 16).
Several people made useful comments including
> From: Tim Bradshaw <tfb@cley.com>
>
> X should be able to use as many bits as the screen has. I suspect the
> problem is a pseudocolour/truecolour. The default visual on the Sun
> (if it's old and has only 8 bit colour) will be pseudocolour, which
> will work. The default visual on the PC may well be truecolour, and
> I'm not at all sure that XAllocColorCells makes any sense for a
> truecolour visual (as there is no colourmap).
>
> You can find out what the default visual is by looking at xdpyinfo for
> the screen.
Right. This works
xdpyinfo | grep bit
> You can often set what the default visual is when the server starts.
> You should also be able to alter the program to make sure it gets a
> visual it can handle.
>
> The whole colour business under X is mysterious and difficult (I have
> a screen with some odd visuals and things like overlay planes, and
> many programs just break on it).
> From: ug55aes@cs.bham.ac.uk (Andrew E Sayers)
>
> > The Sun has an 8 bit colour display whereas the PC uses 24 bits (I
> > think). But I don't think that can be the cause of the problem.
> > (X uses only 8 bits anyway??)
>
> XFree86 (which Linux is probably using) can use non-8 bit colour, and
> some programs do complain at it for doing so.
>
> So long as you've got an 8-bit display mode set up, you can do `startx -
> --bpp 8` (I think it's - --, but it might be -- - or just --) to get it to
> start up in 8 bit mode; alternatively ctrl-alt-+ (on the number pad) will
> cycle through all the available modes while you're running X (is that
> XFree86-specific?)
Unfortunately the DEL laptop doesn't have a number pad.
However, with help from Jonathan Sloman I managed to undo the
default setup which started X with XDM when the machine boots, and
found that this command:
startx -- -bpp 8
does indeed start X running with only 8 bit colour. And then the
popvision library works fine on the linux machine.
This is obviously only a short term fix. We need to find out how to
modify the low level utilities so that they can display grey scale
images etc. on a screen with more bitplanes.
But it is nice to know that it is possible to get popvision working,
as it has lots of nice features for displaying and processing
images.
Aaron
==
--
Aaron Sloman, ( http://www.cs.bham.ac.uk/~axs/ )
School of Computer Science, The University of Birmingham, B15 2TT, UK
EMAIL A.Sloman AT cs.bham.ac.uk (NB: Anti Spam address)
PAPERS: http://www.cs.bham.ac.uk/research/cogaff/
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