Bradley,
On May 24, 2008, at 9:07 PM, Bradley Vance wrote:
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
bgbackground (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.
I think you're still missing the point - it is the fill. I suspect
you're misunderstanding the effect of using semi-transparent strokes.
Moreover I get *exactly* the same result using X11 (both Mac *and*
Linux) as well as other devices (PDF etc.). If you see anything else
then *that* is a bug.
A point is represented by a shape (path) which is filled and then
drawn (line stroke). As I was trying to explain earlier the effect is
that half of the line is in the filled area. Imagine a rectangle (0,0)-
(1,1). When you fill it, you're filling strictly the area between 0
and 1 (in both x and y). However, when you strike let's say the line
(0,0)-(1,0) with the width 0.25, you are filling the area (0,-0.25)-
(1,+0.25) which means that half the line is outside (y<0) the filled
are and another half is inside (y>=0). Given the alpha-blending
mechanics [target=alpha*color + (1-alpha)*old] it implies that if the
fill color is different from the background color and the line is not
opaque, you get different color outside and inside the rectangle. You
can verify that this is true for all devices that support alpha
blending. This is how it works and is supposed to be, that's not a bug.
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,
Well, 2.6 didn't have alpha support in X11 AFAIR, so I have no idea
what you are trying to compare there ...
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...
Again, I think you are missing something - it behaves consistently on
Linux and Mac in the latest release and it's not a bug.
Cheers,
Simon
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, [EMAIL PROTECTED] 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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