[R] grob questions

[Gabor Grothendieck]

On 10/4/05, Paul Murrell <p.murrell at auckland.ac.nz> wrote:
> Hi
>
>
> Gabor Grothendieck wrote:
> > On 10/4/05, Paul Murrell <p.murrell at auckland.ac.nz> wrote:
> >
> >>Hi
> >>
> >>
> >>Gabor Grothendieck wrote:
> >>
> >>>If I run the following example from:
> >>>http://www.stat.auckland.ac.nz/~paul/grid/doc/grobs.pdf
> >>>
> >>>
> >>>
> >>>>grid.newpage()
> >>>>pushViewport(viewport(w = 0.5, h = 0.5))
> >>>>myplot <- gTree(name = "myplot", children = gList(rectGrob(name = "box",
> >>>
> >>>+ gp = gpar(col = "grey")), xaxisGrob(name = "xaxis")))
> >>>
> >>>
> >>>>grid.draw(myplot)
> >>>>grid.edit("myplot::xaxis", at = 1:10/11)
> >>>>grid.edit("myplot::xaxis::labels", label = round(1:10/11, 2))
> >>>>grid.edit("myplot::xaxis::labels", y = unit(-1, "lines"))
> >>>
> >>>
> >>>then
> >>>
> >>>
> >>>
> >>>>str(myplot$children$xaxis)
> >>>
> >>>
> >>>lists 'at' but not the 'labels'.
> >>>
> >>>yet if I do this then the labels are listed:
> >>>
> >>>
> >>>
> >>>>xx <- xaxisGrob(name = "myX", at = 1:10)
> >>>>childNames(xx)
> >>>
> >>>[1] "major"  "ticks"  "labels"
> >>>
> >>>
> >>>1. How do I get to labels in the first case?
> >>
> >>
> >>First, if the xaxisGrob has at=NULL then it calculates its tick-marks at
> >>drawing time (based on the viewport it gets drawn in).  So it does not
> >>store any labels (it doesn't know what they are until it gets drawn). If
> >>you specify a non-NULL 'at' then the axis creates labels.
> >>
> >>Second, grid grobs are standard R objects (copy-on-modify) so the object
> >>'myplot' is not the same object that is being modified by the calls to
> >>grid.edit().  grid.edit() destructively modifies a copy of the grob that
> >>grid has stored on its display list;  you refer to the appropriate grob
> >>via its name (not via an R object).  By comparison, editGrob() takes a
> >>grob and returns a modified copy of the grob, for example ...
> >
> >
> > Just one clarification.  What is the scope of names?
> > In a recent post
> >
> >   https://www.stat.math.ethz.ch/pipermail/r-help/2005-October/078653.html
> >   https://www.stat.math.ethz.ch/pipermail/r-help/2005-October/078656.html
> >
> > it seems that one had to use absolute paths and that seems to be the
> > case here too where as mkondrin pointed out earlier in this thread
> >
> >   https://www.stat.math.ethz.ch/pipermail/r-help/2005-October/078635.html
> >
> > that get.grid("myplot::xaxis::labels")$label works.
> >
> > Its not clear to me whether names:
> >
> > - must be in absolute paths
> > - can be relative to some position under some conditions
> > - are global across all grob names in use and can be referred to directly
> > as long as they are unique among all grobs defined so far.
> >
> > It seems absolute path names work but I am not sure whether the
> > other possibilities can work under some conditions too.
> >
> > Also what the scope of viewports?   Absolute path? Relative path?
> > Global names?  Does it work the same way?  I think at least
> > absolute and relative paths are avalable here but could you confirm
> > my understanding and whether the situation is the same for
> > viewports and grobs?
> >
> > (In the Windows, and analogously in UNIX, file system one can write
> > \usr\myname or position oneself to \usr using cd and then refer to
> > myname in a relative way:
> >
> > cd \usr
> > dir myname
> > )
>
>
> The distinction is not between "relative" or "absolute" paths, but
> between "strict" and "not strict" paths.
>
> Matching a path always *starts* from your current "position" (so in that
> sense it is always "relative" and never "absolute").  When working with
> viewports, there is a current viewport tree and it is possible to be in
> different positions within that tree --- via [push|down|up]Viewport()
> --- so a path may have different meanings depending on where you are.
> (The seekViewport() function is sort of absolute because it always
> starts from the root of the viewport tree, but a non-strict
> seekViewport() [see below] behaves quite differently from an absolute
> filesystem directory path.)  When working with grobs, you tend to always
> be at the "top" or "root".  You are either: working off-screen with a
> single specific grob (gTree) so you are always at the top of that gTree;
>  or working with the grid display list, in which case you have a list
> of grobs and gTrees, which are searched one after the other.
>
> The functions that take paths for grobs, such as grid.edit(), and for
> viewports, such as downViewport(), have an argument 'strict' which
> controls whether the path should be matched from the current position or
> whether the search can start from the current position and we'll match
> the path if it occurs anywhere below the current position.  (There are
> also 'grep' and 'global' arguments so you can get multiple matches where
> it makes sense.)
>
> In some cases, grid has to make use of a path on its own, without
> knowing explicitly whether the path is strict (e.g., when you specify a
> path in a 'vp' slot).  In those cases, grid interprets the path as
> strict (so that, for example, grid has some chance of undoing the
> navigation down to a viewport).
>
> Regarding uniqueness of names, all viewports *which share the same
> parent viewport* must have unique names (same for grobs).  You can,
> however, have several grobs with the same name on the display list.
> i.e., the following produces two separate grobs on the display list
>
> grid.rect(name="rect")
> grid.rect(name="rect")
>
> Does that make things any clearer?
>


That certainly helps although some examples would be nice.

1. I understand that in the original example:

	grid.newpage()
	pushViewport(viewport(w = 0.5, h = 0.5))
	myplot <- gTree(name = "myplot",
	  children = gList(rectGrob(name = "box", gp = gpar(col = "grey")),
		  xaxisGrob(name = "xaxis")))
	grid.draw(myplot)
	grid.edit("myplot::xaxis", at = 1:10/11)
	grid.edit("myplot::xaxis::labels", label = round(1:10/11, 2))
	grid.edit("myplot::xaxis::labels", y = unit(-1, "lines"))

we can do this:

	grid.get("myplot::xaxis::labels")$label

and without specifying complete paths it can be done like this:

	get.grid("labels")$label

so I am ok on this one.


2.  But going back to:

 https://www.stat.math.ethz.ch/pipermail/r-help/2005-October/078653.html
 https://www.stat.math.ethz.ch/pipermail/r-help/2005-October/078656.html

I see you mention that vp= is always strict so is there a way to
do this somehow:

library(grid)
vp <- vpTree(
	viewport(layout=grid.layout(2,2), name="layout"),
	children=vpList(
		viewport(layout.pos.col = 1, layout.pos.row=1, name="tl"),
		viewport(layout.pos.col = 2, layout.pos.row=2, name="br")
	)
)

grobs <- gList(
	rectGrob(vp=vpPath("layout","tl")),
	textGrob("Top left", vp=vpPath("layout","tl")),
	textGrob("Bottom right", vp=vpPath("layout","br"))
)

grid.draw(gTree(childrenvp=vp, children = grobs))

without repeating "layout" three times in the definition of the
grobs object?