Hi
baptiste auguie wrote:
Dear all,
In an attempt to draw fill patterns in grid graphics, I have
encountered a behavior of grobX that I cannot understand from the
documentation. Consider this,
library(grid)
## gTree
g1 <- gTree(children=gList(
rectGrob(0.5,0.5, width=unit(0.8,"npc"),
height=unit(2,"cm")),
circleGrob(r=0.3)), vp=viewport(0.5,0.5))
## gList
g1 <- gList(rectGrob(0.5,0.5, width=unit(0.8,"npc"),
height=unit(2,"cm")),
circleGrob(r=0.3))
## loop over angles to map the boundary
gtheta <- function(g, theta){
sapply(theta, function(.t){
gx <- convertX(grobX(g, .t), "npc")
gy <- convertY(grobY(g, .t), "npc")
c(gx,gy)
})
}
angles <- seq(0,360,by=30)
p1 <- gtheta(g1, angles)
grid.newpage()
grid.draw(g1)
grid.points(p1[1,],p1[2,], gp=gpar(cex=0.2),
default.units="npc")
If I'm not mistaken, neither gList nor gTree seem to produce the
documented behavior,
"If the grob describes multiple shapes, the boundary value will either
correspond to the edge of a bounding box around all of the shapes
described by the grob (for multiple rectangles, circles, xsplines, or
text), or to a convex hull around all vertices of all shapes described
by the grob (for multiple polygons, points, lines, polylines, and
segments)."
That description is referring to a single *grob* object that draws
multiple shapes, something like ...
g1 <- circleGrob(x=1:3/4, y=1:3/4, r=.1)
... in your example.
The behaviour of gTrees is pretty much undefined, but the user is free
to slap a class on the gTree and write their own xDetails() and
yDetails() methods to achieve the outcome that they want. I have
wondered about supplying a default that makes some sort of union of the
boundaries of the children of a gTree, but have not yet implemented that.
The gList case has been explicitly coded to produce the result from the
last object in the gList, but I cannot recall why I ever thought that
might be a good default. Again, making the gList the children of a
gTree with a specific class provides the opportunity to control what
grobX() and grobY() return for yourself.
Paul
with gList, I observe that the boundary is only considered for the
first shape, whilst gTree ignores all children altogether.
It works fine for single shapes (e.g. g1 = circleGrob(r=0.3)).
The same behavior is observed with quartz(), pdf() and png().
Sincerely,
baptiste
sessionInfo()
R version 2.12.1 Patched (2010-12-30 r53895)
Platform: i386-apple-darwin9.8.0 (32-bit)
locale:
[1] en_GB.UTF-8/en_GB.UTF-8/C/C/en_GB.UTF-8/en_GB.UTF-8
attached base packages:
[1] grid stats graphics grDevices utils datasets
methods base
loaded via a namespace (and not attached):
[1] tools_2.12.1
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--
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x85392
p...@stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/
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