Thanks for the suggestion. I believe it is exactly what I need. I will try this function. Thanks!
Regards, Shu Fai On Mon, Oct 16, 2023 at 3:39 AM Paul Murrell <p...@stat.auckland.ac.nz> wrote: > > 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 > > > > ______________________________________________ > > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > > https://stat.ethz.ch/mailman/listinfo/r-help > > <https://stat.ethz.ch/mailman/listinfo/r-help> > > PLEASE do read the posting guide > > http://www.R-project.org/posting-guide.html > > <http://www.R-project.org/posting-guide.html> > > and provide commented, minimal, self-contained, reproducible code. > > -- > 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 > p...@stat.auckland.ac.nz > www.stat.auckland.ac.nz/~paul/ > ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
