From kcrisman at gmail.com  Wed Apr 20 14:35:39 2011
From: kcrisman at gmail.com (Karl-Dieter Crisman)
Date: Wed, 20 Apr 2011 08:35:39 -0400
Subject: [Rd] How to get R to compile with PNG support
Message-ID: <BANLkTik8Tr1nucaDUQvNM9socPz6wNhvJg@mail.gmail.com>

> Message: 12
> Date: Wed, 20 Apr 2011 02:09:23 -0700 (PDT)
> From: Sharpie <chuck at sharpsteen.net>
> To: r-devel at r-project.org
> Subject: Re: [Rd] How to get R to compile with PNG support
> Message-ID: <1303290563237-3462502.post at n4.nabble.com>
> Content-Type: text/plain; charset=UTF-8
>
>
> 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.

Good morning, Charlie et al.,

Thanks for your words.  We like R, too!  We need to advertise it more,
and this thread is part of making sure that happens in the long run.

To the issue at hand.   Our main concern is just not to have to spend
hours reading the configuration and makefile to figure out exactly
where things happen.


>>
>> 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.


True.  It's the device enabling that I'm talking about.  We enable
aqua on Mac, and png on Linux.

We ignore Cairo, and ignore X11 on Mac because it is too touchy (at
least, according to the FAQ on this - different weird instructions for
each type, and of course not everyone has X on Mac).

> 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.
>

Great.  That is okay with us; we aren't expecting (yet) people to be
able to save R graphics in various output formats.  Our native
(matplotlib) graphics, we do expect this.


>> 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.
>>


> 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.

Gotcha.  I suspect that the X11 not listed under Interfaces is the
problem (again, we ignore Cairo).

What is the *exact* file or directory that the R configure looks for
in trying to list X11 under Interfaces?   And is there any way around
this at all?  That is, is there any way for R to create but not
display a graphic if it has (for instance) png support, like the one
on the Trac ticket did?  We can always just search for the png file
and serve it up in our own viewers.

Note that we already search for /usr/include/X11/Xwindows.h, and
adding xorg-dev didn't help with the latest one (which may not be on
the Trac ticket).


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

Yes, I just referenced that for reference, as it were.

Thank you, and I hope we can get this resolved!

Karl-Dieter



[Rd] How to get R to compile with PNG support
Karl-Dieter Crisman