From paul at stat.auckland.ac.nz  Mon Apr 24 05:10:34 2017
From: paul at stat.auckland.ac.nz (Paul Murrell)
Date: Mon, 24 Apr 2017 15:10:34 +1200
Subject: [Rd] polypath winding rule with transparency
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Message-ID: <2f75ae4a-2596-196a-6f9d-5d16c4fa5c6f@stat.auckland.ac.nz>


Thanks for the additional information.  I see the behaviour that you are 
reporting (on Windows), which is pretty weird behaviour!
Hopefully this will shed some light on the other problem that you 
reported, rather than being another unrelated problem.

Paul

On 24/04/2017 1:37 p.m., Michael Sumner wrote:
>
>
> On Thu, 4 Aug 2016 at 17:53 Michael Sumner <mdsumner at gmail.com
> <mailto:mdsumner at gmail.com>> wrote:
>
>     On Thu, 4 Aug 2016 at 11:17 Paul Murrell <paul at stat.auckland.ac.nz
>     <mailto: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 <http://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
>         <mailto: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 <mailto: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 <mailto: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
>

-- 
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/



[Rd] polypath winding rule with transparency
Paul Murrell