[Plplot-devel] Should plgetpos be part of the common API or plP_gvpd and plP_gvpw?

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

Alexandre Gobbo and friends have suggested some python API as follows:

static char doc_getpos[]="transforms window coordinates into graphic coordinates";

static PyObject * pl_getpos(PyObject *self, PyObject *args)
{
	PLINT x,y;
	PLINT inside=1;
	PLFLT xmin,xmax,ymin,ymax;
	PLINT w,h;
	PLFLT posX, posY;
	PLStream *pls;

	PyObject *result;
	TRY (PyArg_ParseTuple(args, "iiii", &x,&y, &w,&h));
	plgpls(&pls);   // pls points directly to a structure PLStream

	xmin=pls->vpdxmi*(PLFLT)w;
	xmax=pls->vpdxma*(PLFLT)w;
	ymin=pls->vpdymi*(PLFLT)h;
	ymax=pls->vpdyma*(PLFLT)h;

	if      ((x < xmin)||(x > xmax)||(y < ymin)||(y > ymax)) inside=0;

	if      (x < xmin)	x=(PLINT)xmin;
	else if (x > xmax)	x=(PLINT)xmax;
	if      (y < ymin)	y=(PLINT)ymin;
	else if (y > ymax)	y=(PLINT)ymax;

	posX=  pls->vpwxmi + (((PLFLT)x-xmin)*(pls->vpwxma-pls->vpwxmi)/(xmax-xmin));
	posY=  pls->vpwyma - (((PLFLT)y-ymin)*(pls->vpwyma-pls->vpwymi)/(ymax-ymin));


	result = Py_BuildValue(PL_ARGS("(idd)", "(iff)"),inside, posX, posY);
	return result;
}

w, and h (width and height from the pyqt GUI environment) and x and y are
supplied, and the flag "inside" and  posX and posY are returned.

I want to discuss some alternatives to this approach here because I am
allergic to special PLplot API for each individual front end.

So here is one question I would like you to consider.  Would this general
functionality be useful for the common API for other GUI's?  If so, I would
strip all the python stuff out and make it generally available as common API
and then add a python wrapper to this new common API so Gobbo et al.
would have access to it from python.

If not generally useful, then I will suggest they do this logic in python
using the values of pls->vpdxmi, etc., and pls->vpwxmi, etc. returned from
the PLplot environment.

Before looking at how to retrieve the values, I have looked carefully at how
these values are set for the PLplot environment.  pls->vpdxmi, etc. are
generated in either c_plsvpa (called from c_plenv) and c_plvpor, and
pls->vpwxmi, etc. are generated by c_plwind (called on its own or from
c_plenv).

These values are retrieved from the PLplot environment using the plP_gvpd
and plP_gvpw functions.  Currently these functions are part of the public C
API, but are meant for internal PLplot use and are not currently part of the
common API.

So if some overall functionality like the C part of the code above does not
become part of the common API with a python wrapper, then instead I would
convert plP_gvpd and plP_gvpw to common API, and provide python wrappers.

Which choice is better?

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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