[Rd] Buggy trellis.focus() with xyplot ?

[Deepayan Sarkar]

On Wed, Nov 19, 2008 at 8:55 AM, Daniel Kornhauser
<dkor at northwestern.edu> wrote:
> Hi:
>
> (Tried to find a bug report about this issue, but was unable to find it, let
> me know if this is a known issue)
> I have been working on an interface to highlight xyplot panels on mouse
> overs in JavaGD but I have stumbled with what seems to be a bug in
> trellis.focus.
> I am using R 2.8 with lattice 0.17-15
>
>
> *** To replicate the bug:
> 1.- display an xyplot. For example, from the xyplot help page:
> library(lattice)
> require(stats)
> EE <- equal.count(ethanol$E, number=9, overlap=1/4)
> ## Constructing panel functions on the fly; prepanel
> xyplot(NOx ~ C | EE, data = ethanol,
>       prepanel = function(x, y) prepanel.loess(x, y, span = 1),
>       xlab = "Compression Ratio", ylab = "NOx (micrograms/J)",
>       panel = function(x, y) {
>           panel.grid(h=-1, v= 2)
>           panel.xyplot(x, y)
>           panel.loess(x,y, span=1)
>       },
>       aspect = "xy")
> 2.- resize to window be rectangular and have large margins in the left hand
> and right hand side.
> 3.- run trellis.focus() and try to select the first or last panel, you
> should observe that it does not select the right one.
>
> sidenotes:
> There are other problems with the focus in JavaGD but I just wanted to
> include a simple self contained example in this mail.
> If you make the window smaller, trellis.focus() works fine, you have to make
> it bigger than the initial size.
>
>
> *** To Fix the bug:
> I tried to fix this bug in interraction.R but I was unsuccesful.
>
> The problem should stem from the a bad calculation of the pads in the
> follwoing lines :
>        leftPad <-
> convertX(sum(glayout$page.layout$widths[1:(colRange[1]-1)]), "npc",
> valueOnly = TRUE)
>        rightPad <-
> convertX(sum(glayout$page.layout$widths[(colRange[2]+1):layCols]), "npc",
> valueOnly = TRUE)
>        topPad <-
> convertY(sum(glayout$page.layout$heights[1:(rowRange[1]-1)]), "npc",
> valueOnly = TRUE)
>        botPad <-
> convertY(sum(glayout$page.layout$heights[(rowRange[2]+1):layRows]), "npc",
> valueOnly = TRUE)
>
> I was succesful in tweaking the follwing lines adding arbitrary constants to
> make it work for a particular instance of a xyplot with a particular size of
> a window
>       clickXScaled <- (as.numeric(clickLoc$x) - leftPad + Danielconstant1)
> / (1 - leftPad - rightPad  + Danielconstant1)
>        ....
>        clickYScaled <- (as.numeric(clickLoc$y) - botPad + Danielconstant2)
> / (1 - botPad - topPad + Danielconstant3)
> This is of course a useless fix, since you want the fix to work for any plot
> with any window size, but I might be valuable information.
>
>
> *** Questions:
> - Is this a real bug ?
> - Any suggestions for fixing it ?
> - If it can't be fixed, is there a way around this bug ?
> (For example, setting the margins to be zero and set a fixed size for the
> xplot)

It appears that the conversions used in the current implementation
(contributed by Felix Andrews) don't work when aspect != "fill"
(probably leading back to the use of 'respect = TRUE' in grid.layout).
The right way to do this is to first go down to the subregion
containing just the panels, and then locate the click location within
it. But this requires a suitable viewport to be predefined.

I have changed print.trellis to create such a dummy viewport
(accessible by trellis.focus("figure")), and modified trellis.focus()
to use it. I will test it a bit more before uploading a new version
(and also give Felix a chance to see if this breaks anything in
playwith etc.). To see if the fix works, you can try the svn copy at

https://svn.r-project.org/R-packages/trunk/lattice

-Deepayan