[Plplot-devel] Dropped remaining use of pltr0f from our Fortran binding

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

Hi Arjen:

I have been looking at how we use pltr0(f) in both our old and new
Fortran bindings, where pltr0f differs from pltr0 by an offset of 1 in
the index transformation.

The pltr0f callback was used for PLCON07 and PLVEC07 (plcont and plvec
signatures without callback-related arguments (i.e., no trailing xg,
yg, tr, or callback arguments), but these overloaded versions of
plcont and plvect were not actually tested in our examples and were
not documented.  If anybody ever actually used that signature for the
old binding I believe they would find that offset of 1 on what, after
all, is the value of a C index is problematic since it means that the
Fortran plot results would be shifted by 1 unit from the corresponding
C results.

Since I view that offset of 1 used by pltr0f as problematic, I decided
to implement our plcont signature without callback-related arguments
using pltr0 rather than pltr0f some while ago, and I have now (commit
55a6de0) done the same for our plvect signature without
callback-related arguments.  The result is we no longer have use for
plplot_private_pltr0f so I have removed that routine from the
plplot_private_exposed module as of the same commit.

As part of that same commit, I have documented the backwards
incompatibilities for these particular plcont and plvect signatures in
README.release. However, I have also noted this is "for the record"
documentation because these signatures were unlikely to be used by
anybody since they were not documented or used in any of our examples.

To complete this story concerning signatures for the case of no callback-related
arguments, in our new Fortran binding we internally use a NULL C
callback for the case where the Fortran signatures of plshade,
plshades, and plimagefr have no callback-related arguments. To me this
approach (lack of Fortran arguments maps to NULL callback) just makes
sense philosophically.  Furthermore, the NULL C callback is a signal
to the C versions of plshade, plshades, and plimagefr to map the index
ranges of the results to the xmin, xmax, ymin, and ymax arguments of
those routines without bothering with using a callback to do this
mapping. (The plcont and plvect C routines have no xmin, xmax, ymin,
and ymax arguments so a NULL callback is not allowed for those two
cases.)

I have confirmed that our old Fortran binding also used a NULL C
callback for plshade and plshades (see PLSHADE07, and PLSHADES07), but
that binding used pltr0 rather than NULL for the plimagefr (see
PLIMAGEFR07) case.  In retrospect I think that was a mistake for our
old binding (although that mistake made no difference for our examples
because pltr0 applies an identity transformation to the index range of
x and y, and the xmin, xmax, ymin, and ymax arguments happen to
correspond to their index ranges in example 20 where this signature is
used).  As of commit 0258c58 I have documented this backwards
incompatibility in README.release.

Please let me know if you have any strong objections to the approach
I have taken for the case where the signatures of plcont, plshade,
plshades, plimagefr, and plvect have no callback-related arguments.

Alan
__________________________
Alan W. Irwin

Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).

Programming affiliations with the FreeEOS equation-of-state
implementation for stellar interiors (freeeos.sf.net); the Time
Ephemerides project (timeephem.sf.net); PLplot scientific plotting
software package (plplot.sf.net); the libLASi project
(unifont.org/lasi); the Loads of Linux Links project (loll.sf.net);
and the Linux Brochure Project (lbproject.sf.net).
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Linux-powered Science
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