[Rd] seekViewport error

[Gabor Grothendieck]

On Jan 23, 2008 9:38 PM, Paul Murrell <p.murrell at auckland.ac.nz> wrote:
> Hi
>
>
> Gabor Grothendieck wrote:
> > Why does the seekViewport at the bottom give an error?
>
>
> Because the viewport is popped after GRID.cellGrob.84 is drawn.
>
> grid.ls() shows the viewport because it recurses down into the legend
> frame grob.  Compare your output with (grid-generated numbering differs)
>  ...
>
>  > grid.ls(recurs=FALSE, view=TRUE)
> ROOT
>   GRID.rect.28
>   plot1.toplevel.vp
>     plot1.xlab.vp
>       plot1.xlab
>       1
>     plot1.ylab.vp
>       plot1.ylab
>       1
>     plot1.strip.1.1.off.vp
>       GRID.segments.29
>       1
>     plot1.strip.left.1.1.off.vp
>       GRID.segments.30
>       GRID.text.31
>       1
>     plot1.panel.1.1.off.vp
>       GRID.segments.32
>       GRID.text.33
>       GRID.segments.34
>       1
>     plot1.panel.1.1.vp
>       GRID.points.35
>       GRID.points.36
>       GRID.points.37
>       1
>     plot1.panel.1.1.off.vp
>       GRID.rect.38
>       1
>     plot1.legend.top.vp
>       GRID.frame.9
>       1
>     plot1.
>       1
>     1
>
> If you look at what viewports are actually available, via
> current.vpTree(), you'll see that GRID.VP.24 is not there.
>
> The problem (see also
> https://stat.ethz.ch/pipermail/r-help/2008-January/151655.html) is that
> cellGrobs (children of frame grobs) use their 'vp' component to store
> the viewport that positions them within the parent frame.  This means
> that the viewport is pushed and then popped (as per normal behaviour for
> 'vp' components).
>
> A possible solution that I am currently trialling uses a special
> 'cellvp' slot instead so that the cellGrob viewports are pushed and then
> "upped".  That way they remain available after the cellGrob has drawn,
> so you can downViewport() to them.
>
> The disadvantage of this approach is that the viewports no longer appear
> in the grid.ls() listing (because grid.ls() has no way of knowing about
> special components of grobs that contain viewports).  This effect can
> already be seen by the fact that the viewport for the frame grob
> (GRID.frame.70) is not shown in the grid.ls() output.  On the other
> hand, the viewports will be visible via current.vpTree()  ...

Perhaps some convention could be adopted which, if followed, would
let grid.ls know?  If that worked at least for graphics generated from
lattice and ggplot2 that would likely satisfy a significant percentage
of uses.