Transparent grid lines

Question

I want to create transparent lines with the grid package.

This works (only for horizontal and vertical lines):

require(grid)
grid.newpage()
grid.rect(x=0.5, y=0.5, width=0, height=0.5, gp=gpar(col=rgb(1, 0, 0, .4)))

However, this doesn't:

grid.newpage()
grid.lines(x=c(0.5, 0.5), y=c(0.25, 0.75), gp=gpar(col=rgb(1, 0, 0, .4)))

I tried this both in RStudio v0.97.237 and in RGui 2.15.2.

UPDATE: when I put this second code chunk in a function, such as in the dothegrid() in the first answer below, it does work in RStudio, but only after a restart, of after clicking "Clear All" in RStudio's plot device pane.

UPDATE2: now we're getting somewhere: It only works when clicking on "Clear All" in RStudio, followed by the grid.lines statement (WITHOUT the grid.newpage() statement)

Answer 1

I don't think the proble is due to newpage command.

I play with units :

this doesn't work

 grid.newpage()
 grid.lines(x,y,   gp=gpar(col='red'),default.units = "npc")

But when I change the default units this work :

 grid.newpage()
 grid.lines(x,y,   gp=gpar(col='red',alpha=0.4),default.units='naif')

Notice that that naif is used when you pass the functions a numeric vector without any associated units.

Answer 2

Not an answer, just some details

require(grid)

dothegrid <- function(){
  grid.newpage()
  grid.lines(x=c(0.5, 0.5), y=c(0.25, 0.75), gp=gpar(col=rgb(1, 0, 0, 0.2)))
  grid.lines(x=c(0.4, 0.4), y=c(0.25, 0.75), gp=gpar(col=rgb(1, 0, 0, 0.6)))
}

# Window 7
# Make sure to restart RStudio/R before running this
dothegrid() # Rstudio: ok, nothing in RGui
# run again
dothegrid() # makes the lines disappear

pdf("a.pdf")
dothegrid()
dothegrid() # lines stay
dev.off()

png("a.png")
dothegrid() #lines stay
dev.off()

R version 2.15.2 (2012-10-26) Platform: x86_64-w64-mingw32/x64 (64-bit)

locale: [1] LC_COLLATE=German_Germany.1252 LC_CTYPE=German_Germany.1252
[3] LC_MONETARY=German_Germany.1252 LC_NUMERIC=C
[5] LC_TIME=German_Germany.1252

attached base packages: [1] grid stats graphics grDevices utils datasets methods base