Bug#408666: bold attribute causes some glyphs to fail rendering

[Ivan Shmakov <oneingray@gmail.com>]

>>>>> Francesco Poli <frx@firenze.linux.it> writes:
>>>>> On Tue, 14 Jul 2009 12:35:38 +0200 Sam Hocevar wrote:

[…]

 >> I can confirm the problem. It seems to be due to uxterm failing to
 >> render bold glyphs, as the following example shows:

 >> echo ▜; tput bold; echo ▜

 >> The second “▜” is rendered using the replacement character.
 >> Copy-pasting that character yields the original “▜” glyph.

 > Yes, I can reproduce the issue this way too.  I am using xterm/243-1:
 > the above command should feed the BTS version tracking accordingly...

	While this bug is caused by the very same lack of glyphs in the
	fonts XTerm is configured to use (and its inability to use,
	roughly, more than one at a time), I believe it's an issue
	sufficiently distinct from #449480 and #469943 (which were
	merged in some three years ago), as it arises in the case of
	discrepancies in the coverage between the -medium- and -bold-
	variants of the same font.

	It seems to me that this issue is somewhat deeper, as (according
	to xterm(1)) it's possible to configure XTerm to ignore the bold
	variant altogether and to rely on “overstruck” shapes instead:

--cut: xterm(1) --
  alwaysBoldMode (class AlwaysBoldMode)

      Specifies whether xterm should check if the normal and bold fonts
      are distinct before deciding whether to use overstriking to
      simulate bold fonts.  If this resource is true, xterm does not
      make the check for distinct fonts when deciding how to handle the
      boldMode resource.  The default is "false."

      boldMode   alwaysBoldMode   Comparison   Action
      ────────────────────────────────────────────────────
      false      false            ignored      use font
      false      true             ignored      use font
      true       false            same         overstrike
      true       false            different    use font
      true       true             ignored      overstrike
--cut: xterm(1) --

	However, using $ xterm -xrm '*alwaysBoldMode: true' still
	doesn't prevent XTerm from using the -bold- variant (as noticed
	by missing glyphs.)  The resource itself is not overridden, as
	per editres(1).

	OTOH, if (assuming default fonts) we're to switch to the “Huge”
	font via the Ctrl+Button3 “Unicode Fonts” menu, the overstruck
	shapes are used, as the font selected has no -bold- variant at
	all.

	(The code below was used to generate the test set of
	characters.)

$ (s=$(perl -we 'use strict; binmode (STDOUT, ":utf8");
                 foreach my $i (64 .. 95, 0x2580 .. 0x259f) {
                     printf ("U+%04x : ", $i) if ($i % 16 == 0);
                     printf ("%s%s", chr ($i), ($i % 16 == 15 ? "\n" : ""));
                 }') ; \
      tput bold ; printf %s\\n "$s" ; \
      tput sgr0 ; printf %s\\n "$s") 

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