Re: [R] transforming output of grid.locator() to coordinates of a leaf viewport

From: Wittner, Ben, Ph.D. <Wittner.Ben_at_mgh.harvard.edu>
Date: Tue, 03 Jun 2008 08:43:01 -0400

Paul,

Thanks very much! Your example code below shows exactly how to do what I wanted.

-Ben

p.s., For the record,
transRight <- current.transform()
after the second call to pushViewport() seems to have gotten deleted from you example code below, but that was obvious.

> -----Original Message-----
> From: r-help-bounces_at_r-project.org [mailto:r-help-bounces_at_r-project.org]
> On Behalf Of Paul Murrell
> Sent: Monday, June 02, 2008 10:05 PM
> To: Wittner, Ben, Ph.D.
> Cc: r-help_at_stat.math.ethz.ch
> Subject: Re: [R] transforming output of grid.locator() to coordinates of a
> leaf viewport
>
> Hi
>
>
> Wittner, Ben, Ph.D. wrote:
> > Hadley, In my application the leaf viewports will not overlap, but I
> guess that
> > would not necessarily be the case for all applications. In any event, do
> you
> > happen to know how to transform coordinates in the top-level viewport to
> > coordinates in another viewport in the tree? Thanks. -Ben
>
>
> current.transform() transforms from *inches* within the current viewport
> to *inches* on the overall device. Sounds like you need the inverse
> transform.
>
> If you are in a position to be able to enumerate all of your leaf
> viewports, then this may be a possible approach:
>
> - for each leaf viewport, visit the viewport and record the
> current.transform() for each leaf viewport. Also record the size of the
> current viewport (in inches).
> - capture a click on the device (current viewport should be ROOT) in
> *inches*, then iterate through the leaf viewports to determine which one
> was clicked in.
> - to determine whether the click was within the viewport, use something
> like the following function (and check whether both new locations are
> positive and smaller than the size of the viewport (in inches)):
>
> newloc <- function(loc, trans) {
> temploc <- c(loc, 1) %*% trans
> (temploc/temploc[3])[-3]
> }
>
> Here's a simple example:
>
> # two "leaf" viewports
> # (one on the left half of the device, one on the right)
> grid.newpage()
> pushViewport(viewport(x=0, width=.5, just="left", name="left"))
> transLeft <- current.transform()
> sizeLeft <- c(convertWidth(unit(1, "npc"), "inches", valueOnly=TRUE),
> convertHeight(unit(1, "npc"), "inches", valueOnly=TRUE))
> # Draw a rect for visual reference
> grid.rect(gp=gpar(fill=hcl(240, 60, 80)))
> upViewport()
> pushViewport(viewport(x=.5, width=.5, just="left", name="right"))
> sizeRight <- c(convertWidth(unit(1, "npc"), "inches", valueOnly=TRUE),
> convertHeight(unit(1, "npc"), "inches", valueOnly=TRUE))
> heightRight <- convertHeight(unit(1, "npc"), "inches", valueOnly=TRUE)
> grid.rect(gp=gpar(fill=hcl(120, 60, 80)))
> upViewport()
>
> # Get a click
> # (current viewport is the ROOT viewport)
> click <- grid.locator(unit="inches")
>
> # For each leaf viewport, calculate where the click was
> leftClick <- newloc(unlist(click), solve(transLeft))
> rightClick <- newloc(unlist(click), solve(transRight))
>
> # Which one was it in ?
> all(leftClick > 0 & leftClick < sizeLeft)
> all(rightClick > 0 & rightClick < sizeRight)
>
>
> Does that help ?
>
> Paul
>
>
>
> > ________________________________
> >
> > From: hadley wickham [mailto:h.wickham_at_gmail.com]
> > Sent: Sun 6/1/2008 3:24 PM
> > To: Wittner, Ben, Ph.D.
> > Cc: r-help_at_stat.math.ethz.ch
> > Subject: Re: [R] transforming output of grid.locator() to coordinates of
> a leaf
> > viewport
> >
> >
> >
> > Ben,
> >
> > What if the click occurs over multiple viewports?
> >
> > Hadley
> >
> > On Mon, Jun 2, 2008 at 6:50 AM, Wittner, Ben, Ph.D.
> > <Wittner.Ben_at_mgh.harvard.edu> wrote:
> >> Short form:
> >>
> >> How do I transform the output of grid.locator() (or
> >> grid.locator(unit='npc')) to the native (or npc) coordinates of a
> viewport
> > other
> >> than the top-level viewport?
> >>
> >> Thanks in advance. -Ben
> >>
> >> Long form:
> >>
> >> I would like the user to be able to click anywhere on
> the R
> >> graphics window. I would then like to figure out which leaf viewport
> the user
> >> clicked in and compute the native coordinates in that leaf viewport of
> the
> >> user's click.
> >>
> >> I saw a 2005 response by Paul Murrell to a post by Gabor
> >> Grothendieck roughly on this topic in which Paul suggested looking at
> >> trellis.focus(). I've looked at trellis.focus() and
> trellis.clickFocus(), but
> >> they don't appear to do what I want in that a) it would appear that my
> user
> >> would have to click twice, once to specify which leaf viewport and then
> again
> > to
> >> specify which point in that viewport and b) trellis.clickFocus()
> appears to
> > use
> >> lots of information from the trellis package, which I'm not using.
> >>
> >> So I decided to try to figure out the native coordinates
> of the
> >> click in each leaf viewport, to a) see whether the click is within the
> > plotting
> >> region for that viewport and b) use those coordinates to take the
> appropriate
> >> action if it is. But I don't seem to be able to figure out how to
> translate
> > from
> >> the top-level viewport coordinates to those of a leaf viewport. I tried
> >> interpreting the 3X3 matrix returned by current.transform() as an
> affine
> >> transformation in the x,y plane in homogeneous coordinates, but could
> make no
> >> sense of what I was getting.
> >>
> >> Thanks for any help. -Ben
> >>
> >>
> >>
> >>
> >> The information transmitted in this electronic
> communica...{{dropped:16}}
> >>
> >> ______________________________________________
> >> R-help_at_r-project.org mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> >> and provide commented, minimal, self-contained, reproducible code.
> >>
> >
> >
> >
> > --
> > http://had.co.nz/
> >
> >
> >
> > The information transmitted in this electronic
> communica...{{dropped:16}}
> >
> > ______________________________________________
> > R-help_at_r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> > and provide commented, minimal, self-contained, reproducible code.
>
> --
> Dr Paul Murrell
> Department of Statistics
> The University of Auckland
> Private Bag 92019
> Auckland
> New Zealand
> 64 9 3737599 x85392
> paul_at_stat.auckland.ac.nz
> http://www.stat.auckland.ac.nz/~paul/
>
> ______________________________________________
> R-help_at_r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-
> guide.html
> and provide commented, minimal, self-contained, reproducible code.

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