[Rd] grid.cap() requires more time?

[Simon Urbanek]

Baptiste,

first, there is a mailing list specifically for Mac questions - R-SIG-Mac.

Now to your post - grid.cap captures the screen of the device which has two implications here:

a) Quartz is asynchronous -- i.e. is doesn't actually draw the content on screen until you're finished with drawing (for efficiency). Unfortunately R has no provision to tell the graphics device that it's done with drawing (you can always add another lines() etc.) so Quartz is simply guessing by measuring the time between draw commands. So when you run grid.cap while the output has not been drawn yet (i.e. immediately after the last drawing command) it will be empty as there is no content yet since Quartz is waiting for the end.

b) it will contain the resize mark because it is a screen shot so the mark is actually part of it (this is intentional).

If what you really want is a bitmap from the device, it's better to use quartz.save instead (followed by readPNG if you want the bitmap as raster) -- that actually re-runs the plot in a separate quartz device that is not on-screen so neither of the above are an issue. 

That said, you can file a) as a bug against Mac version of R (at https://bugs.r-project.org/ ) since grid.cap should actually trigger the flush before it does the capture. I cannot promise that the fix will make it to 2.11.0, though, because it may be non-trivial to trigger the asynchronous flush and wait for it without blocking something (I'll have to look).

Thanks,
Simon


On Apr 17, 2010, at 6:34 AM, baptiste auguie wrote:

> Dear all,
> 
> I am puzzled by the following behavior of the new grid.cap() function,
> which appears to run out of time when capturing the output of a
> graphic. It works fine if I introduce a Sys.sleep(1) before executing
> more code,
> 
> library(grid)
> 
> quartz()
> grid.circle(gp=gpar(fill="black"))
> gg <- grid.cap()
> dev.new()
> grid.raster(gg) ## completely blank
> gg[gg!="white"] ## indeed
> 
> quartz()
> grid.circle(gp=gpar(fill="black"))
> Sys.sleep(1)
> gg <- grid.cap()
> dev.new()
> grid.raster(gg) ## OK
> gg[gg!="white"]
> 
> I tried to see if the problem was limited to the quartz() device but
> for some reason the x11() device is not working for me in this R
> version,
> 
> capabilities(what = NULL)
>    jpeg      png     tiff    tcltk      X11     aqua http/ftp
> sockets   libxml     fifo   cledit    iconv      NLS  profmem    cairo
>    TRUE     TRUE     TRUE     TRUE    FALSE     TRUE     TRUE
> TRUE     TRUE     TRUE     TRUE     TRUE     TRUE     TRUE     TRUE
> Warning message:
> In doTryCatch(return(expr), name, parentenv, handler) :
>  unable to load shared library
> '/Library/Frameworks/R.framework/Resources/modules/i386/R_X11.so':
>  dlopen(/Library/Frameworks/R.framework/Resources/modules/i386/R_X11.so,
> 6): Library not loaded: /usr/X11/lib/libpng12.0.dylib
>  Referenced from:
> /Library/Frameworks/R.framework/Resources/modules/i386/R_X11.so
>  Reason: Incompatible library version: R_X11.so requires version
> 42.0.0 or later, but libpng12.0.dylib provides version 36.0.0
> 
> sessionInfo()
> R version 2.11.0 RC (2010-04-16 r51754)
> i386-apple-darwin9.8.0
> 
> locale:
> [1] en_GB.UTF-8/en_GB.UTF-8/C/C/en_GB.UTF-8/en_GB.UTF-8
> 
> attached base packages:
> [1] grid      stats     graphics  grDevices utils     datasets
> methods   base
> 
> loaded via a namespace (and not attached):
> [1] tools_2.11.0
> 
> I would appreciate if someone could confirm this behavior. Pointers to
> a fix for the x11() device on my machine are also welcome!
> 
> Best regards,
> 
> baptiste
> 
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