Thanks a lot for introducing these functions! I am not aware of them but it seems that they can help me to do what I want to do.
Regards, Shu Fai Regards, Shu Fai Cheung (張樹輝) On Mon, Oct 16, 2023 at 12:24 AM Duncan Murdoch <murdoch.dun...@gmail.com> 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 PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
