[Plplot-devel] New cgm driver

[Alan W. I. <ir...@be...>]

Andrew has recently contributed a cgm driver to plplot.  Frankly, I had
never heard of cgm so I checked it out with google and apparently that
graphics format is used quite a bit by the military and in the oil
business.  Also, it is a vector format rather than bitmapped.  Thus,
for those two reasons I am glad he added this capability to plplot.

The downside of the cgm format is its weak support under Linux.  (Wild
speculation: perhaps the "throw-money-at-it" style of software development
for oil businesses and the military reduced or delayed the pressure to
develop free software that works with the cgm format.) Andrew did manage to
find libcd (see cgm.c for a reference), an unmaintained but working free
library upon which he based his driver.  (This is also available from the
cgmdraw rpm from SuSe, and to be absolutely sure this library does not
disappear on us, I have put a copy of the tarball into our file release
area.)

Another aspect of the weak support for cgm under Linux is the lack of tools
to display cgm results. The only free package I could find to do this is
ralcgm.  Again, this package is unmaintained. Furthermore, in its raw (1995)
form it does not configure under Linux. Fortunately, I was able to get a
linux patch by deconstructing a Linux source rpm that has been made of this
package.  With that patch applied and one workaround, ralcgm configured and
built on Linux.  If anybody else here wants to use this package to view the
cgm results, I can give you the necessary cookbook to make it work.

I have just now put changes into cvs so that Andrew's cgm driver can be built
either dynamically or statically under Linux.  I have run plplot-test.sh
with the cgm driver both for the dynamic and static version of the cgm
driver, and there are no segfaults or other fatal errors.  Furthermore,
identical files are produced in both cases.

These test results did indicate some colour problems. For example for the
5th page of x08c there were lots of error messages about:

Problem setting cmap1 in CGM driver
Problem setting cmap0 in CGM driver.

Also, the gray shading on the 3D shaded plot result seems to be more
non-uniform (more missing triangles) than usual.  I assume it has something
to do with the large number of different grey scales in this example.
Andrew, will you try x08c -dev cgm -fam on your system to see if you get the
same errors for the fifth page?

I also noticed background colour problems.  The X driver output from ralcgm
was OK (i.e., had the black background), but the postscript results from
ralcgm had a white background.  I looked further into this with the
particularly simple x02c example.  I used ralcgm to produce a clear text
version of the x02c cgm, and that had no mention of background colour or
filling.  Andrew, if you have tools to convert from cgm to other formats
such as the clear text version of cgm or postscript, I would appreciate your
confirmation of this problem.  I notice you have done something special with
the background colours in cgm.c, and there may be some logic you need to
change there.

Once these colour problems are sorted out, I should be able to look a bit
closer at the remaining large number of results produced by plplot-test.sh
for the cgm driver.  But so far it looks promising (i.e., no segfaults which
is a big plus as far as I am concerned!)

Andrew, please give my changes a try (if they have any affect in your
environment) and also please run the bug confirmations I have asked for.

Alan

email: ir...@be...
phone: 250-727-2902	FAX: 250-721-7715
snail-mail:
Dr. Alan W. Irwin
Department of Physics and Astronomy,
University of Victoria, P.O. Box 3055,
Victoria, British Columbia, Canada, V8W 3P6
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