Re: [Plplot-devel] Implementing locate mode for all bindings and interactive devices and implementing plmergeopts for all bindings

[Jerry <lan...@qw...>]

On Mar 24, 2014, at 3:18 PM, Alan W. Irwin <ir...@be...> wrote:

> Hi Arjen:
> 
> Thanks for responding to Moez' question on plplot-general concerning
> interative Fortran possibilities.  I think we are all agreed with the
> two goals you stated of having interactive support for all our
> language bindings and each of our interactive devices.  And it is also
> pretty clear we need to implement plmergeopts for all our bindings. So
> I would like to start discussion here of all three of those topics.
> 
> 1. Interactive support for all our language bindings.
> 
> The fundamental issue here is the argument of plGetCursor is a pointer
> to a PLGraphicsIn struct, and C structs like that are not supported by
> most languages we support now.  For example, although plGetCursor does
> appear to have a binding for the Octave case, that function is
> completely ignored for the rest (Python, Java, and Lua) of our
> swig-generated bindings, and I assume it is also ignored for most/all
> of our bindings that are not generated by swig.

FWIW, Ada implements this.
Jerry

> 
> So I think the best way forward here is to define a (c_)plgcursor function
> which wraps plGetCursor and whose arguments are a list of PLINT and
> PLFLT pointers to all the kinds of information currently contained in
> the PLGraphicsIn struct.  If everybody is in agreement on that general
> approach, then it should be straightforward to propagate the proposed
> (c_)plgcursor function to all our language bindings.
> 
> 2. Interactive support for the PLESC_GETC escape code for each of our
> interactive devices.
> 
> I did my own survey of our important interactive devices, and (in
> agreement with what you said on plplot-general) I think the only important
> interactive device missing this capability is the wingcc driver.
> 
> @Argen: does the Windows API used for the wingcc device support the
> possibility of returning cursor information?  If so, getting this
> device up to speed with the remaining interactive devices should be
> straighforward.
> 
> 3. Implementation of (c_)plmergeopts and propagating it to all bindings
> 
> Topics 1 and 2 discuss the changes needed to support the locate mode
> in example 1 for all bindings and for each of our interactive devices.
> But that brings up a related issue which is that we should also have
> complete language bindings for plMergeOpts (renamed to (c_)plmergeopts
> as appropriate for a function in our public API).  This would allow us
> to use the -locate option for example 1 in any language.
> 
> This should be straightforward except for one issue which is that both
> the first and 3rd arguments to plMergeOpts are currently arrays of
> _either_ pointers to strings _or_ NULL. Languages support NULL
> arguments in a wide variety of ways (if they support them at all).  So
> I think a much better thing to do would be to drop that second
> alternative and instead use the empty string (a concept supported by
> all languages) for the same purpose as the current NULL.
> 
> Question for those here who are familiar with use of plMergeOpts, and
> all the argument parsing.  Is there any reason not to use the empty
> string this way?  For example, would an empty string have a normal use
> which would preclude using it as a substitute for the current NULL
> which is used to mark holes in the options table as well as the final
> array element.
> 
> In any case, once we arrive at consensus on how to deal with this
> issue, the implementation should be straightforward.
> 
> 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).
> __________________________
> 
> Linux-powered Science
> __________________________
> 
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