What does X11cairo followed by a number mean in R

I was wondering what does X11cairo in the following mean

> pdf("1_4.pdf")
> plot(output)
> dev.off()
X11cairo 
       2 

Also sometimes the number following X11cairo is 2, sometimes is 1. What does the number imply?

Thank开发者_运维问答s!

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See the Value: section of the help page for dev.off():

‘dev.off’ returns the number and name of the new active device (after the specified device has been shut down).

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I believe the number refers to the number of the active "device" which take numbers 1 - 63. If you have a plot window open and then run the above code, the active device becomes number 2 and so forth. Check out ?dev.off for more details.

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I don't know what you are more interested in, but I want to know why it is called "cario".

see Cario lib page:

Cairo is a graphics device for R which uses the cairo graphics library to provide high-quality output in various formats including bitmap (PNG, JPEG, TIFF), vector (PDF, PostScript, SVG) and on-screen (X11, Windows). It supports alpha-blending (semi-transparent painting), anti-aliasing and font embedding. Since the same engine is used for rendering on-screen and off-screen, is possible to create output WYSIWYG-like output.