[Rd] graphics bugs: steep slopes and large values beyond ylim (PR#414)

[bolker@zoo.ufl.edu]

  Some of my students have uncovered some apparent graphics bugs in 
R.  I think they may manifest slightly different on different platforms/
with different display devices (they sometimes report a Windows graph
that looks OK but odd results on printing).
  I'm able to replicate similar problems on my Linux (RH 6.0) system.


1. abline() plots nothing, or a wrong line, when the slope is too steep.

plot(0:10,0:10)
abline(a=0,b=100)
abline(a=0,b=200)
abline(a=0,b=300)
abline(a=0,b=80)

2. when plotting with type "l" and with values far beyond the limits of
the plot, semi-random lines appear on the plot.

plot(exp(1:100),ylim=c(0,10),type="l")

Any thoughts?  I poked a little bit at this myself: abline calls GLine, neither of them
seems to do much checking whether the endpoints of the line to be drawn are way outside of the
window (I guess that XDrawLine, which gets called by GLine, can't handle this).
I guess this should probably be fixed at the the level of GLine (it might fix both of
the above problems, but I'm a little bit afraid digging this deeply into the graphics drivers.
  Maybe it will be obvious to someone closer to the code?

--please do not edit the information below--

Version:
 platform = i686-unknown-linux
 arch = i686
 os = linux
 system = i686, linux
 status = 
 major = 0
 minor = 99.0
 year = 2000
 month = February
 day = 7
 language = R

Search Path:
 .GlobalEnv, Autoloads, package:base

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