Improve CJK support with new values for `.cflags'.

This patch introduces three new values to `.cflags':

  don't break before character: 128
  don't break after character:  256
  allow inter-character break:  512

They are handled differently if compared to other cflags values:

  (1) hcode values are completely ignored
  (2) similar to kern values, and contrary to the other cflags
      values, troff looks at pairs of characters to decide whether a
      break gets inserted

A yet-to-be-written patch should add inter-character spacing if
those flags are active; currently, only zero-width breakpoints are
inserted.

* src/roff/troff/charinfo.h (charinfo): Change type of `flags' to
`int'.  Update callers accordingly.
New enum values `DONT_BREAK_BEFORE', `DONT_BREAK_AFTER', and
`INTER_CHAR_SPACE'.
New member functions `prohibit_break_before',
`prohibit_break_after', and `inter_char_space'.
* src/roff/troff/input.cpp: Updated.

* src/roff/troff/node.cpp (inter_char_space_node): New class similar
to kern_pair_node, collecting charinfo entities with the
abovementioned cflags values.
(break_char_type): Add new enum values.
(glyph_node::merge_glyph_node): Handle abovementioned cflags values
and emit an `inter_char_space_node' if necessary.

* tmac/ja.tmac: Use new cflags values.

* doc/groff.texinfo, NEWS, man/groff_diff.man: Document new values.

1 files changed, 25 insertions, 1 deletions

diff --git a/man/groff_diff.man b/man/groff_diff.man
index e0d355ea..408d7bf7 100644
--- a/man/groff_diff.man
+++ b/man/groff_diff.man
@@ -993,7 +993,6 @@ Lines can be broken after the character (initially characters
 have this property); a line is not broken at a character with this
 property unless the characters on each side both have non-zero
 hyphenation codes.
-
 This can be overridden with value 64.
 .
 .IP 8
@@ -1021,8 +1020,33 @@ have this property).
 Ignore hyphenation code values of the surrounding characters.
 Use this in combination with values 2 and\~4 (initially no characters
 have this property).
+.
+.IP 128
+Prohibit a line break before the character, but allow a line break after the
+character.
+This works only in combination with flags 256 and 512 and has no effect
+otherwise.
+.
+.IP 256
+Prohibit a line break after the character, but allow a line break before
+the character.
+This works only in combination with flags 128 and 512 and has no effect
+otherwise.
+.
+.IP 512
+Allow line break before or after the character.
+This works only in combination with flags 128 and 256 and has no effect
+otherwise.
 .RE
 .
+.IP
+Contrary to flag values 2 and\~4, the flags 128, 256, and 512 work pairwise.
+If, for example, the left character has value 512, and the right character
+128, no line break gets inserted.
+If we use value\~6 instead for the left character, a line break after the
+character can't be suppressed since the right neighbour character doesn't
+get examined.
+.
 .TP
 .BI .char\  c\ string
 [This request can both define characters and glyphs.]