I sent this to R-Help and the listed maintainer of cairoDevice, I hope that
was the right thing to do.

For some reason, Cairo_png puts a box around a figure when you call
plot.new. It looks like box was called with black and a transparent
background. Example:
> library(cairoDevice)
> Cairo_png('cairo.png')
> plot.new()
> dev.off()
null device
          1

The boarder is narrow, so it's hard to see with a stand-alone image viewer.
If you paste the png onto a white background it's quite clear.

Admittedly, the default for par("bg") is transparent, par("bty") is "o" and
par("col") is black. However, this behavior is not consistent with other
devices (such as png in grDevices even if I set par(bg="white")). Also,
Cairo_png draws the box even when par(bty="n").

I just tested this on Debian with version 2.6 of cairoDevice. I've also
observed this behavior on Windows and it's not a new problem.

The only workaround I've found is to call
> Cairo_png()
> par(col="white")
> setHook("plot.new", function() par(col="black"))
> plot(...)

As far as I'm concerned, this is a serious bug, it's a real problem when
creating figures for publication. I'd like confirmation that this is, in
fact, a bug as I haven't seen much documentation for standards for devices.
I suspect that it's a shallow bug, but I've never seen the code for plot.new
nor do_Cairo so my suspicion may be more hope than insight.


Josh Gilbert

Statistical Researcher
Broad Institute
Chemical Biology Program

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