On Fri, Oct 10, 2008 at 2:33 PM, Maurice LeBrun <[EMAIL PROTECTED]> wrote:
> On Friday, October 10, 2008 at 09:10:59 (-0400) Hezekiah M. Carty writes:
>  > On Fri, Oct 10, 2008 at 12:09 AM, Maurice LeBrun <[EMAIL PROTECTED]> wrote:
>  > >  > What do you think of this as a compromise?  Nothing has to be
>  > >  > propagated to other language bindings, and the plgvpw functionality
>  > >  > becomes (I think) more intuitive.
>  > >
>  > > I have to admit to being a little bothered by this change.  The plP_gvpw
>  > > private function is a good way to shield internal workings from this 
> change,
>  > > but begs the larger question: what should plgvpw() actually return?  I 
> can see
>  > > three classes of opinion on the topic:
>  > >
>  > >  1. plgvpw() MUST return exactly what I specified in plwind()
>  > >  2. plgvpw() MUST return exactly what the plot library's actually using
>  > >  3. either is "good enough"
>  > >
>  > > There are good arguments for both 1 & 2.  (2) is what we're using now, 
> moving
>  > > to (1) is the proposal.  The people in category (1) could reverse the 
> delta
>  > > easily enough, as long as it was documented & didn't change.  The people 
> in
>  > > category (2) could do the same, on old code that's long since been 
> forgotten
>  > > about.  The vast majority in (3) will never notice.
>  > >
>  > > As a user, I'm in category (3), and don't *really* care either way.  But 
> be
>  > > aware you are introducing a change that has the potential to change 
> existing
>  > > code behavior.
>  >
>  > Maurice,
>  >
>  > Thank you for your feedback on this.
>  >
>  > My extra argument for position (1) is that, for some viewport
>  > dimensions, the delta is not cleanly reversible due to floating point
>  > rounding errors.  Adding the delta to get the (2) case does not have
>  > this floating point rounding problem so the values for (2) are always
>  > retrievable if the values from (1) are still available.
>
> Ah.. right.  OK, seems a good enough reason to proceed with (1).
>
>  > The proposal is certainly a change to plgvpw's prior behavior.  But
>  > being able to retrieve the case (1) information from PLplot is, I
>  > think, quite important as it relieves the user from having to track
>  > this information which leaves less for the user to keep track of on
>  > their own, and hopefully less room for user error.  It will also make
>  > adding new PLplot-related functions (such as legends or interactions
>  > with external Cairo surfaces) much cleaner since these functions can
>  > retrieve the user-provided information directly from PLplot.
>  >
>  > If it is too close to the 5.9.1 release to consider a change like
>  > this, perhaps it could be reconsidered after 5.9.1 is released?
>
> Maybe better to do it now, so that the issue is still fresh in case any issues
> arise.

Sounds good to me.  If this is acceptable to the rest of the core
PLplot devs then I am quite happy.  Please let me know when/if the
commit hits and I will test it further.

Hez

-- 
Hezekiah M. Carty
Graduate Research Assistant
University of Maryland
Department of Atmospheric and Oceanic Science

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