[R] Plot to a device and examine the plot?

[Paul Murrell]

Hi

You could also look at dev.capture(), depending on which screen device 
you are using.

Paul

On 16/10/23 05:24, Duncan Murdoch wrote:
> On 15/10/2023 12:05 p.m., Shu Fai Cheung wrote:
>  > Let me clarify my question:
>  >
>  > plot.new()
>  > polygon(c(.5, .5, .75, .8), c(.25, .3, .4, .5))
>  >
>  > If the device is an on-screen device, can I check whether a 
> particular area
>  > has anything drawn on it, or, to be precise, whether the color of a
>  > particular area has all pixels equal to the background color. That is, if
>  > the background is white, can I know whether a particular area is white?
>  >
>  > E.g., in the case above, the area bounded by rect(0, 0, .25, .25) is
>  > completely white, while the area bounded by rect(0, 0, .75, .75) is not
>  > because part of border of the polygon, black by default, has been 
> drawn in
>  > this area.
>  >
>  > If the device is an image file, then I can check the color of a pixel. I
>  > would like to know whether I can do the same with an on-screen device.
>  >
> 
> I think the answer is that you can't do that in general. However, in
> general you can copy a plot to a different device using dev.copy() and
> examine it there. It won't be pixel-by-pixel identical, but will
> contain the same components, likely with slightly different scaling and
> positioning if the new device isn't the same as the old one.
> 
> You can also save the commands that drew the plot using recordPlot() and
> redraw it using replayPlot() (which is essentially what dev.copy()
> does), but the format of the object saved by recordPlot() is not
> documented, and is subject to change with R version changes.
> 
> Duncan Murdoch
> 
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-- 
Dr Paul Murrell
Te Kura Tatauranga | Department of Statistics
Waipapa Taumata Rau | The University of Auckland
Private Bag 92019, Auckland 1142, New Zealand
64 9 3737599 x85392
paul using stat.auckland.ac.nz
www.stat.auckland.ac.nz/~paul/