[Rd] polypath winding rule with transparency

Mon Apr 24 03:37:06 CEST 2017

On Thu, 4 Aug 2016 at 17:53 Michael Sumner <mdsumner at gmail.com> wrote:

> On Thu, 4 Aug 2016 at 11:17 Paul Murrell <paul at stat.auckland.ac.nz> wrote:
>
>> Hi
>>
>> Just to clarify, I think this IS a problem with grid.path() as well as
>> polypath().
>>
>>
> Hi, oh dear - sorry about that
>
> I appreciate the deeper explanation, I knew about the id aspect in grid,
> but just forgot in my haste.
>
> I'll be more careful with examples if I find any more clues.
>
>
I've found a possibly related issue, again only on Windows as far as I can
see.

These two plots give different results, the second is completely
transparent rather than the expected light blue region on the left.
Whether it works or not seems to depend on the specific geometry of the
device and *not on the specific xlim interval chosen*. I can get the
problem to come and by interactively resizing the window resulting from the
first plot. Somehow it's related to the intersection-detection of the
filled polygon with the plot region (?).

pp <- matrix(c(0, 0,
               0, 1,
               1, 1,
               1, 0,
               0, 0), ncol = 2, byrow = TRUE)

xlim <- c(0.24, 1.5)  ## ok at xlim[1] = 0.24
## first plot, ok (but also try resizing the window by dragging the left
side out)
plot(pp, main = "winding/transparent", xlim = xlim)
polypath(pp, col = "#ADD8E6E6", rule = "winding")

xlim <- c(0.25, 1.5)
## second plot, not ok
plot(pp, main = "winding/transparent", xlim = xlim)
polypath(pp, col = "#ADD8E6E6", rule = "winding")

Cheers, Mike.

> Cheers, Mike.
>
>
>> For the example you give, grid.path() diverts to drawing a polygon
>> (because there is no 'id' specified), and the NAs in 'x' generate two
>> separate polygons, which get drawn one on top of the other.
>>
>> The correct analogy to the polypath() example is ...
>>
>> x2 <- matrix(x[!is.na(x)], ncol=2)
>> grid.path(x2[,1], x2[,2], id=rep(1:2, each=4),
>>            rule="winding", gp=gpar(="#BEBEBE80"))
>>
>> ... which produces the same (wrong) result as polypath() on Windows.
>>
>> Also, the grid.path() result for your example is NOT the same as the
>> correct result;  we do NOT want a separate shade for the intersecting
>> region when the "winding" fill rule is working correctly.  The fill
>> should be the same across the union of the square regions (this is what
>> Cairo and PDF on Linux produce).
>>
>> Another data point:  the problem is NOT just a matter of getting the
>> rules round the wrong way in the devWindows.c;  using rule="evenodd"
>> produces the SAME result as using rule="winding".
>>
>> One more data point:  this is not JUST a problem with polypath().
>> Creating a self-intersecting polygon and then drawing it, using
>> polygon(), in windows(fillEvenOdd=FALSE) and windows(filleEvenOdd=TRUE)
>> produces exactly the same result.
>>
>> Sadly, none of that helps to explain why the "winding" rule is not
>> working on Windows :(
>>
>> Thanks for reporting the problem - needs more study to find out what is
>> going wrong.
>>
>> Paul
>>
>> On 03/08/16 18:47, Michael Sumner wrote:
>> > Hello,
>> >
>> > it's probably worth adding that this is not a problem with pathGrob,
>> only
>> > polypath.
>> >
>> > This code is sufficient to demonstrate the problem in Windows.
>> >
>> > ## overlapping, both clock-wise
>> > x <- cbind(c(.1, .1, .6, .6, NA, .4, .4, .9, .9),
>> >           c(.1, .6, .6, .1, NA, .4, .9, .9, .4))
>> > ## only a problem on Windows windows() and png()
>> > plot(x);polypath(x, rule = "winding", col = "#BEBEBE80")
>> >
>> > This code shows the same behaviour on different systems/devices.
>> >
>> > ## no problem on Windows/Linux/PNG/PDF ...
>> > library(grid)
>> > grid.newpage()
>> > pushViewport(viewport(0.5, 0.5, width = 1, height = 1))
>> > grid.draw(pathGrob(x[,1], x[,2], rule = "winding", gp = gpar(fill =
>> > "#BEBEBE80")))
>> >
>> > Cheers, Mike.
>> >
>> > On Wed, 3 Aug 2016 at 16:24 Michael Sumner <mdsumner at gmail.com> wrote:
>> >
>> >> Hi, I see different results in png() and pdf() for polypath() on
>> Windows
>> >> when using the "winding" rule
>> >>
>> >> ## overlapping, both clock-wise
>> >> x <- cbind(c(.1, .1, .6, .6, NA, .4, .4, .9, .9),
>> >>           c(.1, .6, .6, .1, NA, .4, .9, .9, .4))
>> >>
>> >> pfun <- function() {
>> >>   plot(x)
>> >>   polypath(x * 0.8 + 0.2,  rule = "winding", col = "#BEBEBE80")
>> >>   polypath(x,  rule = "winding", col = "#BEBEBE80")
>> >> }
>> >>
>> >> ## output  "windows.png/pdf" or "unix.png/pdf"
>> >> label <- .Platform$OS.type
>> >> png(sprintf("%s.png", label))
>> >> pfun()
>> >> dev.off()
>> >> pdf(sprintf("%s.pdf", label))
>> >> pfun()
>> >> dev.off()
>> >>
>> >>
>> >> Visually, the result in the "windows.png" file is as if the "evenodd"
>> rule
>> >> was specified. All other examples unix.pdf, unix.png, windows.pdf give
>> me
>> >> the expected result - which is "all bounded regions shaded grey, with
>> two
>> >> tones for the different regions of overlap". The unexpected result is
>> the
>> >> completely transparent region.
>> >>
>> >> Is this a known/expected difference on Windows?  I see the unexpected
>> >> result in 3.3.1 and in R version 3.3.1 Patched (2016-07-27 r70991) on
>> >> Windows.
>> >>
>> >> Cheers, Mike.
>> >> --
>> >> Dr. Michael Sumner
>> >> Software and Database Engineer
>> >> Australian Antarctic Division
>> >> 203 Channel Highway
>> >> Kingston Tasmania 7050 Australia
>> >>
>> >> --
>> > Dr. Michael Sumner
>> > Software and Database Engineer
>> > Australian Antarctic Division
>> > 203 Channel Highway
>> > Kingston Tasmania 7050 Australia
>> >
>> >       [[alternative HTML version deleted]]
>> >
>> > ______________________________________________
>> > 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. Michael Sumner
> Software and Database Engineer
> Australian Antarctic Division
> 203 Channel Highway
> Kingston Tasmania 7050 Australia
>
> --
Dr. Michael Sumner
Software and Database Engineer
Australian Antarctic Division
203 Channel Highway
Kingston Tasmania 7050 Australia

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