Re: [Plplot-devel] Problems with setting cmap0 and cmap1 for the xfig and png devices

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

On Wed, 10 Jul 2002, [iso-8859-1] Jo=E3o Cardoso wrote:

> the xfig file format stores colors at a fixed position (variable length)
> in the begining of the file; latter changes in the colors will thus
> overwrite the previous color setting, thus the observed results.

Thanks for investigating this case.  However, I don't see how the position
of where the colours are stored in the file matters so long as you are
allowed to add to the colours part way through a plot, and I assume your
variable length remark means you can do that for the xfig format.

Of course this is not a trivial fix.  What you have to do is to have an
additional mapping step to get from the PLplot colours to the xfig ones.  T=
o
take the cmap0 example a step further for the first sub-plot there are 16
PLplot colours which should be mapped to 16 xfig colours. However, when the
first colour index for PLplot cmap0 is changed from red to white for the
remaining sub-plots then there should be an additional 17th white colour
defined in the xfig system which the first cmap0 index for PLplot now maps
to.  But the red colour is still in the xfig colour map so the first
sub-plot with red box and scales should remain unaffected.

>
> I think the same happens for any file based format, and can't be fixed.

No, I don't believe you can generalize this way.  There is no such problem
with the postscript format.  Furthermore, I believe the idea of having a
transformation between the PLplot colour maps and the file device colour ma=
p
as above should solve the problem for all devices which allow you to add to
their colour map part way through a plot.  I believe from what you have
said above this should be possible for the xfig format, and that also seems
to be the case for the libgd format (upon which the png and jpeg devices
are based).

Of course it is easy to sit here and theorize about a solution that will
take considerable work on your part to implement, and I fully understand if
you (or Andrew) don't have time/inclination to deal with this now. But the
current situation is (I believe) that xfig and the libgd-based drivers make
the simplistic assumption that there is a constant one-to-one transformatio=
n
between the PLplot colour maps and the device colour map.  If you do the
work to remove this assumption as above, then the xfig and png plots for th=
e
octave, tcl, and python front ends (which do several examples at a time)
will not have the colour map cross-talk that now occurs.  This will bring
these devices' colour map behaviour finally into line with what occurs for
the psc device which would be a Good Thing....

Alan