[Rd] How to get R to compile with PNG support

[Sharpie]

Dear R devel list,

Good morning; I'm with the Sage (http://www.sagemath.org) project.
(Some of you might have seen my talk on this at last summer's useR
conference).

Thanks for stoping by Karl! I have to say that I am a big fan of the Sage
project---it is a very good idea and I really appreciate all the time you
guys put into it. I may not be able to answer all of your questions
concerning PNG support, but hopefully some of the following pointers will be
useful.



Karl-Dieter Crisman wrote:
> 
> We have some rudimentary support for using R graphics in various
> cases, which has proved useful to many of our users who want to go
> back and forth between R and other capabilities within Sage.
> Unfortunately, the way we originally implemented this was using the
> png and plot functions in R itself, which perhaps isn't the best
> (i.e., everyone uses ggplot now? but I digress).
> 

One important distinction to make is between R graphics functions such as
plot and ggplot, and R graphics *devices*, such as png. The devices provide
back ends that take the R-level function calls and actually execute the
low-level "draw line from a to b, clip to rectangle A, insert left-justified
text at x,y" primitives that get written to an output format.

Bottom line for Sage is that as long as you implement at least one device
function, such as png, your users should be able to call plot, ggplot, and
the rest of R's graphics functions to their heart's content, they just won't
have a wide selection of output formats.



Karl-Dieter Crisman wrote:
> 
> That means that when people download a binary of ours, or compile
> their own, whether R's plot and png functions work depends heavily on
> the rather obscure (to users) issue of exactly what headers are
> present on the compiling machine.
> 
> Unfortunately, it is *very* unclear what actually needs to be present!
>  There are innumerable places where this has come up for us, but
> http://trac.sagemath.org/sage_trac/ticket/8868 and
> http://ask.sagemath.org/question/192/compiling-r-with-png-support are
> two of the current places where people have compiled information.
> 
> The FAQ says, "Unless you do not want to view graphs on-screen you
> need ‘X11’ installed, including its headers and client libraries. For
> recent Fedora distributions it means (at least) ‘libX11’,
> ‘libX11-devel’, ‘libXt’ and ‘libXt-devel’. On Debian we recommend the
> meta-package ‘xorg-dev’. If you really do not want these you will need
> to explicitly configure R without X11, using --with-x=no."
> 
> Well, we don't actually need to view graphs on-screen, but we do need
> to be able to generate them and save them (as pngs, for instance) to
> the correct directory in Sage for viewing.  But we have people who've
> tried to do this in Ubuntu, with libpng and xorg-dev installed, and
> the file /usr/include/X11/Xwindows.h exists, but all to no avail.
> There are almost as many solutions people have found as there are
> computers out there, it seems - slight hyperbole, but that's what it
> feels like.
> 
> We've posted more than once (I think) to the r-help list, but have
> gotten no useful feedback.  Is there *anywhere* that the *exact*
> requirements R has for having
> 
> capabilities("png")
>   png
> FALSE
> 
> come out TRUE are documented?
> 
> Then, not only could we be smarter in how we compile R (currently
> somewhat naively searching for /usr/include/X11/Xwindows.h to
> determine whether we'll try for png support), but we would be able to
> tell users something very precise to do (e.g., apt-get foo) if they
> currently have R without PNG support in Sage.  Again, I emphasize that
> apparently getting xorg-dev doesn't always do the trick.
> 
> We do realize that for most people wanting to use just R, it's best to
> download a binary, which will behave nicely; Sage's "batteries
> included" philosophy means that we are asking for more specialized
> info from upstream, and for that I apologize in advance.  I also
> apologize if I said something silly above, because I don't actually
> know what all these files are - I've just looked into enough support
> requests to have a decent idea of what's required.    We are trying
> not to have to parse the makefile to figure all this out, and possibly
> making some mistake there as well.
> 
> Thank you SO much for any help with this,
> Karl-Dieter Crisman
> for the Sage team
> 


In the trac ticket you linked, the configure output shows PNG is enabled
(I.E. the library was found) but you may be ending up with no support for an
actual png() graphics device due to one of the following

  - configure didn't find Xlib as X11 is not listed under Interfaces
  - configure didn't find cairo as it is not listed under Additional
capabilities

So, although R has the PNG library that is only useful for writing PNG
files. R also needs the Xlib or Cairo libraries to provide drawing
primitives that will create the figures those files will contain.

In the ask.sagemath question the problem appears to be that the user had X11
installed but not libpng.

I hope this helps!

-Charlie

-----
Charlie Sharpsteen
Undergraduate-- Environmental Resources Engineering
Humboldt State University
--
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