[Rd] gpar fill and transparency on devices

[baptiste auguie]

Hi,

Thanks for pointing this out. I do have the book, unfortunately I left
it abroad this year. I would think that such brief mention in ?gpar
could be useful (because that's where one first looks for gpar()
defaults --- which are not listed).

Best regards,

baptiste


On 6 August 2010 00:54, Paul Murrell <p.murrell at auckland.ac.nz> wrote:
> Hi
>
> The help page for "Working with Viewports" (e.g., pushViewport()) has a
> brief mention when talking about the ROOT viewport ...
>
> "The viewport tree always has a single root viewport (created by the system)
> which corresponds to the entire device (and default graphical parameter
> settings)."
>
> ... which is a reasonable place for it because this is a feature of the gpar
> of the ROOT viewport, not of gpars in general.  That mention might be a bit
> hard to find, but a very similar statement is also made in the Section on
> Viewports in the R Graphics book.  That in turn might be hard to find if you
> don't have the book, but that chapter is also available online
> (http://www.stat.auckland.ac.nz/~paul/RGraphics/chapter5.pdf)
>
> It might be worth adding something more explicit about this sort of gotcha
> ...
>
> "Some devices have different default graphics parameter settings, so it is
> not safe to assume that the ROOT viewport will be identical on different
> devices."
>
> ... ?
>
> Paul
>
> On 5/08/2010 8:14 a.m., baptiste auguie wrote:
>>
>> Dear list,
>>
>> I'm puzzled by the graphical output in the following example,
>>
>> library(grid)
>>
>> foo<- function(){
>>   grid.rect(gp=gpar(fill="black"))
>>   print(get.gpar()$fill)
>>   grid.rect(width=0.2,height=0.2)
>> }
>>
>> png("test.png", bg = "transparent")
>> foo()
>> dev.off()
>>
>> png("test1.png", bg = "white")
>> foo()
>> dev.off()
>>
>>
>> It seems that the default value of gpar()$fill is set according to the
>> device background. I couldn't find this documented in ?gpar or in
>> ?png, and it caused a rather puzzling bug in my code (the pdf() output
>> was OK, whilst the png output (default bg to white) was seemingly
>> empty because covered by a white rectangle.)
>>
>> Best regards,
>>
>> baptiste
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>
> --
> Dr Paul Murrell
> Department of Statistics
> The University of Auckland
> Private Bag 92019
> Auckland
> New Zealand
> 64 9 3737599 x85392
> paul at stat.auckland.ac.nz
> http://www.stat.auckland.ac.nz/~paul/
>



-- 
____________________

Dr. Baptiste Auguié

Departamento de Química Física,
Universidade de Vigo,
Campus Universitario, 36310, Vigo, Spain

tel: +34 9868 18617
http://webs.uvigo.es/coloides