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, 21 insertions, 0 deletions

diff --git a/doc/groff.texinfo b/doc/groff.texinfo
index 42cf6166..dc81fb5a 100644
--- a/doc/groff.texinfo
+++ b/doc/groff.texinfo
@@ -9537,6 +9537,27 @@ into your document.  Note, however, that this can lead to bad layout if
 done without thinking; in most situations, a better solution instead of
 changing the @code{cflags} value is to insert @code{\:} right after the
 hyphen at the places which really need a break point.
+
+@item 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
+(see below) and has no effect otherwise.
+
+@item 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
+(see below) and has no effect otherwise.
+
+@item 512
+Allow line break before or after the character.  This works only in
+combination with flags 128 and 256 and has no effect otherwise.
+
+Contrary to flag values 2 and@tie{}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@tie{}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.
 @end table
 @endDefreq