R devel - Feb 2008 - xspline(..., draw=FALSE) fails if there is no open device (PR#10727)

Full_Name: Jari Oksanen
Version:  2.6.2 RC (2008-02-07 r44369)
OS: Linux
Submission from: (NULL) (130.231.102.145)


Even if function xspline() is called with argument draw=FALSE, it requires a
graphics device (that it won't use since it was draw=FALSE). I run into this
because I intended to use xspline within a function (that does not yet draw:
there is plot method for that), and the function failed when called in a virgin
environment. 

Here is an example in a virgin environemt just after starting R:
> out <- xspline(c(0,1,0), c(1,0,1), draw=FALSE)
Error in xspline(c(0, 1, 0), c(1, 0, 1), draw = FALSE) : 
  plot.new has not been called yet
> str(out)
Error in str(out) : object "out" not found

This works:
> plot(0)
> out <- xspline(c(0,1,0), c(1,0,1), draw=FALSE)
> str(out)
List of 2
 $ x: num [1:3] 0 1 0
 $ y: num [1:3] 1 0 1

This won't:
> dev.off()
null device 
          1 
> xspline(c(0,1,0), c(1,0,1), draw=FALSE)
Error in xspline(c(0, 1, 0), c(1, 0, 1), draw = FALSE) : 
  plot.new has not been called yet

R graphics internal are black magic to me. However, it seems that the error
messge comes from function GCheckState(DevDesc *dd) in graphics.c, which is
called by do_xspline(SEXP call, SEXP op, SEXP args, SEXP env) in plot.c even
when xspline was called with draw = FALSE (and even before getting the argument
draw into do_xspline). It seems that graphics device is needed somewhere even
with draw = FALSE, since moving the  GCheckState() test after findig the value
draw, and executing the test only if draw=TRUE gave NaN as the numeric output. 

If this is documented behaviour, the documentation escaped my attention and beg
for pardon. It may be useful to add a comment on the help page saying that an
open graphics device is needed even when unused with draw=FALSE.

Cheers, Jari Oksanen

 platform = i686-pc-linux-gnu
 arch = i686
 os = linux-gnu
 system = i686, linux-gnu
 status = RC
 major = 2
 minor = 6.2
 year = 2008
 month = 02
 day = 07
 svn rev = 44369
 language = R
 version.string = R version 2.6.2 RC (2008-02-07 r44369)

Locale:
LC_CTYPE=en_GB.UTF-8;LC_NUMERIC=C;LC_TIME=en_GB.UTF-8;LC_COLLATE=en_GB.UTF-8;LC_MONETARY=en_GB.UTF-8;LC_MESSAGES=en_GB.UTF-8;LC_PAPER=en_GB.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_GB.UTF-8;LC_IDENTIFICATION=C

Search Path:
 .GlobalEnv, package:stats, package:graphics, package:grDevices, package:utils,
package:datasets, package:methods, Autoloads, package:base

jari.oksanen at oulu.fi wrote:
> Full_Name: Jari Oksanen
> Version:  2.6.2 RC (2008-02-07 r44369)
> OS: Linux
> Submission from: (NULL) (130.231.102.145)
>
>
> Even if function xspline() is called with argument draw=FALSE, it requires
a
> graphics device (that it won't use since it was draw=FALSE). I run into
this
> because I intended to use xspline within a function (that does not yet
draw:
> there is plot method for that), and the function failed when called in a
virgin
> environment. 
>
> Here is an example in a virgin environemt just after starting R:
>
>   
>> out <- xspline(c(0,1,0), c(1,0,1), draw=FALSE)
>>     
> Error in xspline(c(0, 1, 0), c(1, 0, 1), draw = FALSE) : 
>   plot.new has not been called yet
>   
>> str(out)
>>     
> Error in str(out) : object "out" not found
>
> This works:
>
>   
>> plot(0)
>> out <- xspline(c(0,1,0), c(1,0,1), draw=FALSE)
>> str(out)
>>     
> List of 2
>  $ x: num [1:3] 0 1 0
>  $ y: num [1:3] 1 0 1
>
> This won't:
>
>   
>> dev.off()
>>     
> null device 
>           1 
>   
>> xspline(c(0,1,0), c(1,0,1), draw=FALSE)
>>     
> Error in xspline(c(0, 1, 0), c(1, 0, 1), draw = FALSE) : 
>   plot.new has not been called yet
>
> R graphics internal are black magic to me. However, it seems that the error
> messge comes from function GCheckState(DevDesc *dd) in graphics.c, which is
> called by do_xspline(SEXP call, SEXP op, SEXP args, SEXP env) in plot.c
even
> when xspline was called with draw = FALSE (and even before getting the
argument
> draw into do_xspline). It seems that graphics device is needed somewhere
even
> with draw = FALSE, since moving the  GCheckState() test after findig the
value
> draw, and executing the test only if draw=TRUE gave NaN as the numeric
output.
>
> If this is documented behaviour, the documentation escaped my attention and
beg
> for pardon. It may be useful to add a comment on the help page saying that
an
> open graphics device is needed even when unused with draw=FALSE.
>
>   
I think the reason is that 2d splines are aspect ratio dependent.  
There's this loop inside,

    for (i = 0; i < nx; i++) {
        xx[i] = x[i];
        yy[i] = y[i];
        GConvert(&(xx[i]), &(yy[i]), USER, DEVICE, dd);
    }
 
and that will not work without knowing how to convert to device 
coordinates. The default for "border" may get you first, though.  That
seems to be documented incorrectly, by the way.

    -p
> Cheers, Jari Oksanen
>
>  platform = i686-pc-linux-gnu
>  arch = i686
>  os = linux-gnu
>  system = i686, linux-gnu
>  status = RC
>  major = 2
>  minor = 6.2
>  year = 2008
>  month = 02
>  day = 07
>  svn rev = 44369
>  language = R
>  version.string = R version 2.6.2 RC (2008-02-07 r44369)
>
> Locale:
>
LC_CTYPE=en_GB.UTF-8;LC_NUMERIC=C;LC_TIME=en_GB.UTF-8;LC_COLLATE=en_GB.UTF-8;LC_MONETARY=en_GB.UTF-8;LC_MESSAGES=en_GB.UTF-8;LC_PAPER=en_GB.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_GB.UTF-8;LC_IDENTIFICATION=C
>
> Search Path:
>  .GlobalEnv, package:stats, package:graphics, package:grDevices,
package:utils,
> package:datasets, package:methods, Autoloads, package:base
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>   

-- 
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