Macintosh Transperancy (PR#11511)

Simon,
	The bug is that the point that's being plotted is a single point, not
a combination of two points, one that's just the outline, and one
that's just the fill.  It also doesn't look like we'd expect when
you're debugging a plot.  For example, let's say I create a plot, and
notice that I can't see some of the points (due to other points being
drawn on top of them).  So I decide to make them transparent, so you
can see where points over-lay each other, and the relative size/ 
colors/
etc of the over-layed points.  Now, rather than just changing the
opacity of the points/colors I see, I'm adding in another color to
each point where outline and background meet, making the plot more
confusing than it needs to be...
	In looking at the documentation for bg in points (plot says to look
at points for bg) it says
bg
background (fill) color for the open plot symbols given by pch=21:25.
and the way it is now, the color is not a fill (ie - inside the lines)
- it's super-imposed over part of the line.
	Also, there's the fact that it does something different on different
systems.  When I do the same thing at work on a Linux box (we don't
have R.2.7 yet, we use mostly R2.4 but I've tried it on R2.6, and we
don't have Quartz, but I did output to PDF), it looks like a single
point whose colors were made transparent, and not a point made of two
overlapping transparent parts.

	As I implied in my original ticket, I'd like to be able to choose
whether to have it look the way it does now on the mac, and the way it
does on Linux.  This might actually be something that needs to be
addressed further by the core team, as that opacity is planning to be
added for X11() for the next revision (and hopefully, will work into
PNG and other device types that can support it)...
	Perhaps the best way to implement the options/choices/etc is to add a
separate alpha/opacity/whatever options that would control the opacity
of each object it plots.  Thus, if you define an opacity to either col
or bg, it would work the way it does on the Mac (ie - the colors are
opaque and can thus you can see the other point-color through the top
one).  However, if you have a point-opacity defined, the entire point
will get the opacity, the way it is currently done on Linux.
	Or, you can just say that in order to get it look the way that it
currently does on the mac, you need to plot each point twice, once
with no bg, and once with no line...

	Also, I don't think this is a critical bug.  It's just something I
noticed that behaves differently on what I have at work (Linux) and
what I have at home (mac).  I'm impressed with R, and am thinking of
getting more involved in the r-project community, so figured I'd start
with something I noticed was different across platforms...

On May 24, 2008, at 6:17 PM, Simon Urbanek wrote:

Brad,

can you, please, let us know what is the "bug" here? If you paint
semi-transparent line over the same filled shape (same vertices),
clearly half of the line will be inside and and half outside of the
shape, so each part will have a different color - that is the whole
point of semi-transparency. Therefore I fail to see any bug or
unexpected behavior here.

Cheers,
Simon


On May 24, 2008, at 10:55 AM, brdvance at gmail.com wrote:

Full_Name: Brad Vance
Version: 2.7.0
OS: 10.5.2
Submission from: (NULL) (71.123.195.202)


Problem : When drawing transperant points with lines thick-
lines(lwd>1) + fill
(pch=21-25), it looks like the line is transperantly overlayed over
the fill,
making it look like 2-lines surround the fill (each a different
color).  I
actually think that this is a nice OPTIONAL way to draw the points
(even as
default), but since I could not discover how to turn it off, I
decided to issue
the ticket.  In this option can see on the default-quartz device as
well as
PDF-device.

Solution : Have the entire point-object designed/drawn as if there  
is
no-transparency, then make the composite object transparent.
Optionally figure
out an option to determine whether to apply transperancy as a group
(to the
entire object) or separately (as it is now).

Code :

df <- data.frame(X=rnorm(50),Y=rnorm(50))
plot
(X
~
Y
,data
=
df 
,pch=c(21,22,23,24,25),cex=5,col="#00FF0055",bg="#FF000055",lwd=6)

Thanks,
-Brad Vance

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