postscript failure manifests in plot.TukeyHSD

Jari Oksanen <jari.oksanen <at> oulu.fi> writes:

Hello R Developers,

Dear R-developers, 

I ran some standard tests with currently (today morning) compiled R release
candidate in Linux R 2.12.1 RC (2010-12-13 r53843). Some of these tests used
plot.TukeyHSD function. This worked OK on the screen (X11 device), but
PostScript file could not be rendered. The following example had the problem
with me:

postscript(file="tukeyplot.ps")
example(plot.TukeyHSD)
dev.off()

I couldn't view the resulting file with evince in Linux nor in the standard
Preview in MacOS. When I compared the generated "tukeyplot.ps" to the same
file generated with an older R in my Mac, I found one difference:

$ diff -U2 oldtukeyplot.ps /Volumes/TIKKU/tukeyplot.ps
--- oldtukeyplot.ps    2010-12-14 12:06:07.000000000 +0200
+++ /Volumes/TIKKU/tukeyplot.ps    2010-12-14 12:13:32.000000000 +0200
@@ -172,5 +172,5 @@
 0 setgray
 0.00 setlinewidth
-[ 3.00 5.00] 0 setdash
+[ 0.00 0.00] 0 setdash
 np
 660.06 91.44 m

Editing the changed line to its old value "[ 3.00 5.00] 0 setdash" also
fixed the problem both in Linux and in Mac. Evidently something has changed,
and probably somewhere else than in plot.TukeyHSD (which hasn't changed
since r51093 in trunk and never in R-2-12-branch). I know nothing about
PostScript so that I cannot say anything more (and I know viewers can fail
with standard conforming PostScript but it is a bit disconcerting that two
viewers fail when they worked earlier).

I must really be avoiding work today ...

  I can diagnose this (I think) but don't know the best way to 
solve it.

  At this point, line widths on PDF devices were allowed to be <1.

==========
r52180 | murrell | 2010-06-02 23:20:33 -0400 (Wed, 02 Jun 2010) | 1 line
Changed paths:
   M /trunk/NEWS
   M /trunk/src/library/grDevices/src/devPS.c

allow lwd less than 1 on PDF device
==========

  The behavior of PDF devices (by experiment) is to draw a 0-width
line as 1 pixel wide, at whatever resolution is currently being
rendered.  On the other hand, 0-width lines appear to break PostScript.
(with the Linux viewer 'evince' I get warnings about "rangecheck -15"
when trying to view such a file).

  plot.TukeyHSD  contains the lines

abline(h = yvals, lty = 1, lwd = 0, col = "lightgray")
abline(v = 0, lty = 2, lwd = 0, ...)

  which are presumably meant to render minimum-width lines.

  I don't know whether it makes more sense to (1) change plot.TukeyHSD
to use positive widths (although that may not help: I tried setting
lwd=1e-5 and got the line widths rounded to 0 in the PostScript file);
(2) change the postscript driver to *not* allow line widths < 1 (i.e.,
distinguish between PS and PDF and revert to the pre-r52180 behaviour
for PS only).  

  On reflection #2 seems to make more sense, but digging through devPS.c
it's not immediately obvious to me where/how in SetLineStyle or
PostScriptSetLineTexture one can tell whether the current driver
is PS or PDF ...