grid.cap() requires more time?

On Apr 17, 2010, at 2:43 PM, baptiste auguie wrote:

Hi,

On 17 April 2010 18:51, Simon Urbanek <simon.urbanek at r-project.org> wrote:

Baptiste,

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

I wasn't sure if it was Mac-specific (OK, quartz() is but I could not
test x11()).

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.

OK, that makes sense.

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

This design decision surprises me. Would it be possible to have an
option not to capture this mark as well?

I don't think so because the mark is part of the Quartz view - it is not something the device adds so it is not a "design decision". Again I can only repeat that if you want a re-play of the draw commands you should use that instead - it's a different task.

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.

I thought the aim of grid.cap was to make it easier to capture a
bitmap copy (no need to create an external file). Is a screenshot more
useful?

I didn't write grid.cap() so I don't know what the intention was, but "capturing a bitmap copy" is exactly the above (that is why it is called "capture" I suppose). What you are requesting is something different - creating a new bitmap using the same device settings and quartz.save does that. It would be trivial to add a parameter to quartz.save to return the bitmap directly instead of a file, but R did not have direct bitmap support so it was not requested so far.

Cheers,
Simon

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).

Will do.

Thanks,

baptiste

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