Bug#880450: gnuplot: bad right margin when xtics label are rotated and aligned

[Celelibi]

Package: gnuplot
Version: 5.2.0+dfsg1-2
Severity: minor

Dear Maintainer,

When setting labels for xtics, it looks like gnuplot adds some extra
space on the right to accomodate for the text width... if it were left
aligned. Angles 0° and 90° seem to have special case calculation.

This is especially annoying for multiplot when only the rightmost plots
are smaller for no reason.

I attach two gifs and the script to generate them, testing all the xtics
angles. One with the labels left-aligned (the default) one with the
labels right-aligned. The issue should become obvious.

It happens for the three terminals I tested: pngcairo, gif and qt.

Best regards,
Celelibi

-- System Information:
Debian Release: buster/sid
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'unstable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.13.0-1-amd64 (SMP w/8 CPU cores)
Locale: LANG=fr_FR.UTF-8, LC_CTYPE=fr_FR.UTF-8 (charmap=UTF-8), LANGUAGE=fr_FR.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages gnuplot depends on:
ii  gnuplot-qt [gnuplot-nox]  5.2.0+dfsg1-2

gnuplot recommends no packages.

Versions of packages gnuplot suggests:
pn  gnuplot-doc  <none>

-- no debconf information
-------------- next part --------------
A non-text attachment was scrubbed...
Name: xtics_left.gif
Type: image/gif
Size: 307922 bytes
Desc: not available
URL: <http://lists.alioth.debian.org/pipermail/debian-science-maintainers/attachments/20171031/74e41c94/attachment-0002.gif>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: xtics_right.gif
Type: image/gif
Size: 304202 bytes
Desc: not available
URL: <http://lists.alioth.debian.org/pipermail/debian-science-maintainers/attachments/20171031/74e41c94/attachment-0003.gif>
-------------- next part --------------
set terminal gif size 640,480 animate delay 10
set output "xtics_left.gif"
set xrange [0:1]

do for [i=0:360:10] {
	print "Rendering angle ", i
	set xtics ("sometext" 0, "somemoretext" 1) rotate by i left
	set multiplot layout 2,2
	plot x
	plot x
	unset xtics
	plot x
	plot x
	unset multiplot
}

set terminal gif size 640,480 animate delay 10
set output "xtics_right.gif"

do for [i=0:360:10] {
	print "Rendering angle ", i
	set xtics ("sometext" 0, "somemoretext" 1) rotate by i right
	set multiplot layout 2,2
	plot x
	plot x
	unset xtics
	plot x
	plot x
	unset multiplot
}