Bug#931305: xterm: problems with Greek pi (π) and box-drawing

[Protesilaos Stavrou <info@protesilaos.com>]

Package: xterm
Version: 344-1
Severity: normal

Dear Maintainer,

While using proportional fonts, the Greek letter pi (π) is treated as
a box-drawing character or, more likely, as missing from the
proportional font altogether.  This happens _only at certain point
sizes_ AND/OR _only with specific fonts_.

Scenario 1: Greek pi works, but box-drawing does not
----------------------------------------------------

With these settings:

	xterm.vt100.faceName: DejaVu Sans Mono
	xterm.vt100.faceSize: 10
	XTerm.vt100.forceBoxChars: false

The greek letter pi is displayed correctly, but the second vertical line
(drawn with U+2502) is almost the same as the first one (drawn with
U+007C).

Image: https://protesilaos.com/assets/images/attachments/xterm_grpi_boxchars_scenario1.png

Scenario 2: Greek pi does not work, but box-drawing does
--------------------------------------------------------

With these settings:

	xterm.vt100.faceName: DejaVu Sans Mono
	xterm.vt100.faceSize: 10
	XTerm.vt100.forceBoxChars: true

The Greek letter pi is drawn using a fixed-size (bitmap) font.  The
second vertical line is properly displayed using box-drawing characters.

Image: https://protesilaos.com/assets/images/attachments/xterm_grpi_boxchars_scenario2.png

Scenario 3: faceSize: 9.5 forceBoxChars: false works for both
-------------------------------------------------------------

With these settings:

	xterm.vt100.faceName: DejaVu Sans Mono
	xterm.vt100.faceSize: 9.5
	XTerm.vt100.forceBoxChars: false

Everything appears to work as intended.

Image: https://protesilaos.com/assets/images/attachments/xterm_grpi_boxchars_scenario3.png

Scenario 4: Fira Code works using settings from scenarios 1 and 3
-----------------------------------------------------------------

With these:

	xterm.vt100.faceName: Fira Code
	xterm.vt100.faceSize: 10
	XTerm.vt100.forceBoxChars: false

Or this changed:

	xterm.vt100.faceSize: 9.5

Everything seems to work as intended.

Image: https://protesilaos.com/assets/images/attachments/xterm_grpi_boxchars_scenario4.png

Scenario 5: forceBoxChars always breaks Greek letter pi (π)
-----------------------------------------------------------

With these settings:

	xterm.vt100.faceName: Fira Code
	xterm.vt100.faceSize: 10
	XTerm.vt100.forceBoxChars: true

Regardless of typeface, enabling forceBoxChars will always draw the
letter pi in a bitmap font.

Image: https://protesilaos.com/assets/images/attachments/xterm_grpi_boxchars_scenario5.png


-- System Information:
Debian Release: 10.0
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 4.19.0-5-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages xterm depends on:
ii  libc6           2.28-10
ii  libfontconfig1  2.13.1-2
ii  libfreetype6    2.9.1-3
ii  libice6         2:1.0.9-2
ii  libtinfo6       6.1+20181013-2
ii  libutempter0    1.1.6-3
ii  libx11-6        2:1.6.7-1
ii  libxaw7         2:1.0.13-1+b2
ii  libxft2         2.3.2-2
ii  libxinerama1    2:1.1.4-2
ii  libxmu6         2:1.1.2-2+b3
ii  libxpm4         1:3.5.12-1
ii  libxt6          1:1.1.5-1+b3
ii  xbitmaps        1.1.1-2

Versions of packages xterm recommends:
ii  x11-utils  7.7+4

Versions of packages xterm suggests:
pn  xfonts-cyrillic  <none>

-- no debconf information