Re: [Plplot-devel] plGetCursor() return value (was Should plgetpos ...)

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

Thanks, Maurice, for your comment below which inspired me to look further at
the code and documentation.  As my previous posts have shown, I was confused
about the differences between (sub-)pages, viewports, and windows.  But now
I have looked again at the advanced section of the documentation, and it is
all clearly layed out there.

Each (sub-)page can have more than one (possibly overlapping) viewport, and
each viewport can have various windows superimposed by repeated calls to
plwind (with data registered for each plwind call with plP_swin).  The
windows for a given viewport only differ in the world coordinates of their
minimum and maximum x and y values so multiple windows allow you the option
of making single viewport plots with multiple sets of world coordinates. If
you do have multiple sets of world coordinates for a single viewport, the
data for each plwind call are registered with plP_swin with an ascending
windows index.

Note that in normal use there is only one window per viewport and the
viewports don't physically overlap.  But in the most general case we have
overlapping viewports with multiple windows each. Note in c_plcalc_world I
continue to use Paul Casteel's trick of searching backwards through the
windows indices.  Thus, the code finds the last possibly overlapping defined
viewport and last window defined for that viewport that contains the
relative device coordinates.  This completely answers my concern (Maurice
answered it as well) over what happens with multiple viewports per sub-page.
However, the windows (incorrectly named subpage) index currently returned is
something with a very special internal meaning.

Now that I understand this index, I don't see much public use for it. Does
Joao need this index just for extra information for human consumption?  It
won't make much sense unless you repeat all the ifs, ands, and buts from
above in the documentation. Alternatively, if it is meant to be used to
index some information from plplot, I am not aware of any public (much less
common) API that uses this index.

I am now leaning toward changing c_plcalc_world to just return a status in
the argument list and drop the idea of returning the windows index
altogether. That's what I will probably do unless I hear some good arguments
to keep it (especially from Joao since he probably had some specific use in
mind when he originally brought up the possibility of returning this index).

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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On Thu, 28 Feb 2002, Maurice LeBrun wrote:

> I looked at the dox & code, and all looks cool.
>
> My only nit is that the references to "subpage" should be replaced by
> "window".  I like the more general term better since the code should work fine
> even if not using the usual PLplot subpage model.  In fact I originally wrote
> the window registration code with a completely different windowing front-end
> in mind.
>
> --
> Maurice LeBrun    mj...@ga...
>
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