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

[Simon Urbanek]

On Aug 20, 2010, at 1:59 PM, Matt Shotwell wrote:

> 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.
> 

That is all nice, it will require you to hack R (well, there is the Cairo device so you could make the change outside of R instead).

As always, the reason is buried deep inside -- the lack of connection API. If we had that, devices would take a connection instead of the file name and all would be well since you could use in-memory connections instead of files ... ;)

Cheers,
Simon



>> 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
> 
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