Re: [ gnuplot-Feature Requests-927249 ] Allow filledcurve color to based on whether above/below axis

[Ethan M. <merritt@u.washington.edu>]

I'm switching this to the mailing list because it's much more convenient
for discussion than using the SourceForge  interface. 

On Friday 30 April 2004 10:52 am, Petr Milulik wrote:
>
> > 'set style function filledcurve'.
>
> No, this I would not support, currently you cannot use
> "using" for functions.
> However,
>    'a.dat' using 1:2:(sin($1))
> would work.

But currently you can do
	plot sin(x) with filledcurve y1=0.5

The existing patch extends this to
	plot sin(x) with filledcurve below y1=0.5

I had in mind a further extension to allow both
	plot sin(x) with filledcurve below y1=f(x)
	plot 'data' using 1:2 with filledcurve above y1=f(x)

But your suggestion above is a better idea, at least for 
the data case, because it uses existing function evaluation
code:
	plot 'data' using 1:2:(f($1)) with filledcurve

That leaves a few questions:

Do we allow "above" and "below" in this case?
I think it reasonable that
	plot 'data' using 1:2:(f($1)) with filledcurve above
would fill only those areas where $2 > f($1) 

What exactly should be filled if f(x) is undefined at a given x?
Or in the case of two datasets, what if one of the datasets
has a missing value?

> > By contrast, drawing a filled region bounded by two
> > arbitrary curves requires storing twice as much information
> > for the plot.
>
> I don't think that's difficult.

I agree.  I said it would be fairly easy. My only reservation was 
that it requires code changes in more places than the simpler
case of a bounding line.

	Ethan



> At graphics.c:1832:
>  for (i = 0; i < plot->p_count; i++) {
> there is
> 	x = map_x(plot->points[i].x);
> 	y = map_y(plot->points[i].y);
> so plotting wrt 3 columns would have
> 	y2 = map_y(plot->points[i].z);
> ...I think that parser for plotting wrt 3 columns puts the
> 3rd column number into z.
>
> Then the INRANGE/OUTRANGE cases would have to go in between
> crossing points in between those 2 curves using max(y,y2),
> and make a circle -- i.e., instead of finish_filled_curve(),
> it should do the 2nd round back using values min(y,y2).
>
>
> ----------------------------------------------------------------------
>
> Comment By: Ethan Merritt (sfeam)
> Date: 2004-04-30 16:06
>
> Message:
> Logged In: YES
> user_id=235620
>
> Petr wrote>
>
> > I would propose to submit it to cvs, as it is a valuable
> > feature for the curretion version of gnuplot.
>
> Hold off a bit. Steve claims to have found a case where my
> patch gets the sidedness wrong, although so far I have not
> been able to reproduce the problem. We're pursuing the
> discrepancy in private Email.
>
> >Another great enhancement would be
> >   plot 'a.dat' using 1:2:3 with filledcurve
> >where the filled area would be in between
> > y-points of columns 2 and 3.
>
> The ability to fill an area between two curves has been
> requested a number of times before. I thought there was an
> existing RFE here on SourceForge, but I can't see it now.
> Anyhow, this would be a much more extensive change than the
> simple bounding-line patch I gave here. The code to draw
> filled polygons bounded by a line was already present.  All
> I had to do was make sure that any line segment crossing the
> bounding line is broken into two pieces so that no single
> polygon ever spans both sides of the boundary.
>
> By contrast, drawing a filled region bounded by two
> arbitrary curves requires storing twice as much information
> for the plot.  As you show, it requires an additional input
> column. Or, I suppose, two bounding equations in the case of
> 'set style function filledcurve'.  This means that it is
> effectively a new plot style, and would require adding new
> code in a lot of places.  I think this would be fairly easy,
> but still it would be a bigger project than my simple patch
> here. Certainly it goes way beyond what could be considered
> a bug-fix for version 4.0
>
> So yeah, I agree it would be a very nice, fairly
> straightforward addition. But it can wait until the next
> round of development.
>
> ----------------------------------------------------------------------
>
> Comment By: Petr Mikulik (mikulik)
> Date: 2004-04-30 10:00
>
> Message:
> Logged In: YES
> user_id=31505
>
> I like this patch!
>
> I would propose to submit it to cvs, as it is a valuable
> feature for the curretion version of gnuplot.
>
> Another great enhancement would be
>    plot 'a.dat' using 1:2:3 with filledcurve
> where the filled area would be in between y-points of
> columns 2 and 3.
> Could you please try to implement this as well?
>
>
> ----------------------------------------------------------------------
>
> Comment By: Ethan Merritt (sfeam)
> Date: 2004-04-29 22:00
>
> Message:
> Logged In: YES
> user_id=235620
>
> Heh.  A minor, but dramatic, oversight on my part. Here's a
> revised patchset that might actually work.
>
> ----------------------------------------------------------------------
>
> Comment By: Steve Weiss (sweiss_1966)
> Date: 2004-04-29 15:11
>
> Message:
> Logged In: YES
> user_id=939458
>
> It's different, but not correct.  it looks like you figuring out
> the bounding area to fill, you draw a line from the current
> point to the previous data point as opposed to the current
> point to the previous point where the x-axis was crossed (if
> that makes sense).
>
> I have attached a sample image for you to look at.  Please let
> me know if you need a copy of my test script.
>
> Thanks for all the help!
> Steve
>
> ----------------------------------------------------------------------
>
> Comment By: Ethan Merritt (sfeam)
> Date: 2004-04-29 06:26
>
> Message:
> Logged In: YES
> user_id=235620
>
> Give this patchset a try. It adds new modifiers "above" and
> "below" to the filledcurve style. They apply only to the
> case of explicit bounds. For example:
>   plot 'data' with filledcurve above y1=3.4
>
> I have not done much testing of this code.  Please check
> whether it does what you want, and if so give it a thorough
> workout. In particular I did not do anything special for
> curves that go out of range. It may just work, or it may
> need special-case code added.
>
> ----------------------------------------------------------------------
>
> Comment By: Petr Mikulik (mikulik)
> Date: 2004-04-08 09:56
>
> Message:
> Logged In: YES
> user_id=31505
>
> Make your graph by plotting the same curve twice, and
> probably with this trick:
>
>   plot (f(x)>g(x) ? f(x) : 1/0)
>
>
> ----------------------------------------------------------------------
>
> You can respond by visiting:
> https://sourceforge.net/tracker/?func=detail&atid=352055&aid=927249&grou
>p_id=2055

-- 
Ethan A Merritt       merritt@u.washington.edu
Biomolecular Structure Center
Mailstop 357742
University of Washington, Seattle, WA 98195