[Rd] Rserve graphics output [was Re: C or Java code generation]

[Matt Shotwell]

On Fri, 2010-08-20 at 12:58 -0400, Sharpie wrote:
> 
> Donald Paul Winston wrote:
> > 
> > Aren't you the guy who created Rserve?
> > 
> > I'd like to develop a web app so clients can perform exploratory data
> > analysis with their browser with no installed software, not even java (I
> > don't like applets). I thought R would be excellent for this but I need
> > some issues cleared up before I invest a lot of time working with it. 
> > 
> 
> Well, Simon is the one who create Rserve.  However, if you have questions
> about Rserve it may be best to start a new thread or at least change the
> subject header of your message.  This discussion was about creating
> stand-alone executables that use R code for deployment on a desktop.  
> 
> 
> Donald Paul Winston wrote:
> > 
> > It appears R insists on directing plot output to a file. Is their a
> > graphics device that keeps the output in memory so it can be returned to
> > my java app as a stream of bytes? If I have to wait for it to write to a
> > "unique file" and then read it back again then I don't think that's going
> > to work. My web app needs to support hundreds of concurrent clients. 
> > 
> 
> As far as I know all R graphics output that does not go to a screen device,
> such as an X window, must be directed to some sort of file.  I am not aware
> of a graphics device that provides output to something other than a screen
> or a file, but there very well may be such a device in existence.

This was essentially the conclusion of Donald's earlier thread...

> The functionality you could describe could be implemented by writing a R
> graphics device that forwards the R plotting commands to... well anywhere
> you want, really.  As the author of an R graphics device, I can say the
> trickiest part of such an undertaking will be calculating font metrics so
> that R can properly position text in the graphics.  Everything else is very
> straight-forward.

I believe Donald wants the _rendered_ output. That is, a stream of bytes
that represent a png, jpeg, etc. Toward this end, we have already
discussed using an OS-level fifo to avoid disk I/O, and I think this is
the easiest route for Donald. 

Alternatively, Donald might look into the X11 graphics driver, where
Cairo is used to write pngs. In particular, the in_do_saveplot function
(src/main/modules/X11/devX11.c) calls cairo_surface_write_to_png, in
order to save a png to file. Cairo also provides the
cairo_surface_write_to_png_stream function, which might be used to send
png data to a memory buffer (i.e. a raw vector). I don't think it would
be too difficult to modify in_do_saveplot to accommodate this.

> I have plans to write a device that forwards the plotting commands to a
> socket connection that allows another program to execute them.  In my case,
> an Erlang backbone is used to route the results back to web clients using
> websockets.  The idea is to have the plot rendered directly in the client's
> browser using a JavaScript library like RaphealJS.  However, the school year
> is upon me and the project will probably remain on the drawing board until
> next summer.
> 
> 
> Donald Paul Winston wrote:
> > 
> > Is REngine.jar and REngineRserve.jar  all I need in my web app?
> > 
> 
> I can't comment on REngine as I have not used it.
> 
> 
> Donald Paul Winston wrote:
> > 
> > Also, how come their is no shutdown command from the command line for
> > Rserve. I see one in the java client api. Do I have to write my own?
> > 
> 
> I find that on UNIX a SIGTERM, SIGSTOP or SIGKILL signal broadcast using a
> command line utility such as kill does the job.
> 
> -Charlie
> 
> -----
> Charlie Sharpsteen
> Undergraduate-- Environmental Resources Engineering
> Humboldt State University

-- 
Matthew S. Shotwell
Graduate Student 
Division of Biostatistics and Epidemiology
Medical University of South Carolina