Re: [Plplot-devel] Re: Updates to plarrows

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

On 2004-02-11 11:47-0000 Andrew Ross wrote:

>
> Just to update you, I've commited another patch to add a fill option to
> the new plsarrow function. x22c.c now demostrate this too. There is also
> now an equivalent C++ example x22.cc.

A minor issue is the colours.  For example, I believe red labels and box and
yellow vectors on a black background would look better than the current red
on black.

The other issue is the API.  The last time this was discussed on list, the
definitive comment was Maurice's, I believe.

*************
It would be a whole
different API.  Right now we have:

void
plarrows(PLFLT *u, PLFLT *v, PLFLT *x, PLFLT *y, PLINT n,
         PLFLT scale, PLFLT dx, PLFLT dy)

I'd change this to input 2 quantities (Ax_ij, Ay_ij) using the usual function
evaluator approach.  I think a single function pointer but different client
data for each is sufficient.  I'd drop the dx,dy stuff and instead have it
do a pre-pass to determine what the maximum vector length should be so that
vectors don't overlap, taking into account possible coordinate
transformations.  Then the internal entry point would look something like:

plvecf_int(PLFLT (*plf2eval) (PLINT, PLINT, PLPointer),
       PLPointer plf2eval_data1, PLPointer plf2eval_data2,
       PLINT (*defined) (PLFLT, PLFLT, PLPointer),
       PLPointer defined_data,
       PLINT nx, PLINT ny, PLFLT scale,
       void (*pltr) (PLFLT, PLFLT, PLFLT *, PLFLT *, PLPointer),
       PLPointer pltr_data);

where defined() here includes the new client data pointer syntax.

It'd need a nice front-end to it with a suitably picked function evaluator
similar to in pl*cont* and pl*shade*.

Looks like some work.
*************

To substantially simplify this, I would drop the defined part of it (which I
brought up in the first place for the previous thread).  Right now we don't
have "defined" API for plcont, and I really don't think we need it for this
API. But we do need the overall function evaluator stuff.  Somebody will
immediately want to be plotting vector fields for polar coordinates or
irregularly shaped x,y regions, and plcont handles those cases with ease
because of its function evaluator approach.

Andrew, I have got to say that your example 22 already looks pretty good so
I hope we can settle the API issue then extend that and example 22 (with
colour changes and possibly adding a page with a vector field for polar
coordinates) to all the language interfaces.  I would be willing to do all
of that latter project for python, java, fortran, and tcl, but I would leave
to you doing the internal changes to implement the function evaluator
approach along the lines of what Maurice suggested and also the required
changes to the C++ interface and x22.cc.

Alan
__________________________
Alan W. Irwin
email: ir...@be...
phone: 250-727-2902

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

Programming affiliations with the PLplot scientific plotting software
package (plplot.org), the Yorick front-end to PLplot (yplot.sf.net), the
Loads of Linux Links project (loll.sf.net), and the Linux Brochure Project
(lbproject.sf.net).
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