convert textGrob to imageGrob/rasterGrob? - r

Question

Apologies if this is very straightforward. Actually I hope it will be!
I am trying to dynamically create images from text which I can then resize and plot (either stretched or squashed) to produce a motif-type graph.
I started out using images (which I'd generated using png() and ggplot()) and plotting them as annotation_custom()
require(ggplot2)
require(grid)
require(gridExtra)
qplot(c(0,10),c(0,10)) +
annotation_custom(rasterGrob(image=readPNG("1999.png"),x=0,y=0,height=1,width=1,just=c("left","bottom")),
xmin=0,xmax=5,ymin=0,ymax=7.5)
to produce:
This is fine, but it's awkward to create the images dynamically if they are not the same size, using png(), plus it's clunky to persist them to file, so I tried to see if I could use a textGrob:
myText<-"1000"
myTextGrob<-textGrob(myText,just=c("left","bottom"),gp=gpar(fontsize="100",col="red",fontfamily="Showcard Gothic"))
qplot(c(0,10),c(0,10))+annotation_custom(myTextGrob,0,0,0,0)
and got this, which is fine, except....
...it doesn't seem possible to stretch & skew it in the same way as a rasterGrob so my question is - is it possible to create the textGrob and coerce it to a rasterGrob? Or is there another solution which will let me skew/stretch the textGrob?
Thanks in advance!

Answer 1

It doesn't seem easy without creating temporary files. Instead of raster files, you might use vector paths with the grImport package. There are two options to import text,
as a path; it works (example below), but there's no obvious way to bypass the ps to xml conversion step with intermediate files
as a text string; the xml is much shorter in this case, and could be created directly from R, but unfortunately I couldn't find a way to transform the two axes independently.
library(grImport)
scale_text <- function(text="hello world", scale=4, tmp=tempfile()){
tmp.ps <- paste0(tmp, ".ps")
tmp.xml <- paste0(tmp, ".xml")
string.ps <- paste0('%!PS
/Courier % name the desired font
20 selectfont % choose the size in points and establish
% the font as the current one
1 ', scale, ' scale % scale axis
72 500 moveto % position the current point at
% coordinates 72, 500 (the origin is at the
% lower-left corner of the page)
(', text, ') show % stroke the text in parentheses
showpage % print all on the page
')
cat(string.ps, file=tmp.ps)
PostScriptTrace(tmp.ps, tmp.xml)
readPicture(tmp.xml)
}
hello <- scale_text()
grid.newpage()
grid.picture(hello)