[Plplot-devel] Suggested API change for plpoly3

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

The current plpoly3 API is

c_plpoly3(PLINT n, PLFLT *x, PLFLT *y, PLFLT *z, PLINT *draw)

where abs(n) is the dimension of the x, y, z, and draw arrays.

The sign of n is used for an entirely different purpose, if positive, the
points are drawn in a clockwise way, if negative they are drawn
counter-clockwise way, and this direction of drawing combined with the point
data affects the choice of whether the 3D polygon is facing the viewer or
not and whether it will be drawn or not.

On general grounds, I would prefer to separate the two different purposes
(dimensions and clockwise flag) into two separate parameters.  Also, our
python, yorick, and java front ends carry the dimensions of vectors as part
of the array object, and those dimensions cannot be negative.  So in any
case I want to make a C function which is identical to plpoly3 except its
first argument is not allowed to be negative and it has an additional
(sixth) argument which is a clockwise flag.  This C function will be the
one wrapped for python (and presumably the other front ends with vector
objects).

That leaves the question of what to do with plpoly3, and I especially invite
Maurice and Geoffrey to discuss this.  Should we preserve it for a while as
a deprecated function that we will eventually drop? Or should we simply
change the argument list of plpoly3 so that it has the required 6 arguments?
If the latter, does that mean everybody would have to change any programme
that called plpoly3 or would a 5-argument call still work with the 6th
argument being taken as NULL? I am showing my complete ignorance of the
consequences of increasing the number of arguments for a shared library, and
I don't really know what compiler error (if any) or warning would result
from a 5 parameter call to a function which is declared in a header to have
6 parameters.  But I am prepared to be educated on these matters....;-)

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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