Fix and document display of glyphless characters.

 src/xdisp.c (set_cursor_from_row): Fix cursor positioning on
 zero-width characters.
 (syms_of_xdisp) <glyphless-char-display>: Doc fix.
 src/.gdbinit (pgx): Adapt to latest changes in `struct glyph'.
 src/w32term.c (x_draw_glyphless_glyph_string_foreground): Draw the
 box before drawing the glyphs inside it.
 src/dispextern.h (enum glyphless_display_method): Rename
 GLYPHLESS_DISPLAY_HEXA_CODE to GLYPHLESS_DISPLAY_HEX_CODE.  All
 users changed.
 src/term.c (append_glyphless_glyph, produce_glyphless_glyph): Fix
 comments.
 (produce_glyphless_glyph): Enclose "U+nnnn" and "empty box"
 whitespace in "[]", to simulate a box.  Don't use uninitialized
 variable `width'.
 lisp/international/characters.el (glyphless-char-display-control):
 Renamed from glyphless-char-control; all users changed.  Doc fix.
 Signal an error if display method is not one of the recognized
 symbols.
 doc/emacs/rmail.texi (Rmail Coding): Characters with no fonts are not
 necessarily displayed as empty boxes.
 doc/emacs/mule.texi (Language Environments, Fontsets): Characters with no
 fonts are not necessarily displayed as empty boxes.
 doc/emacs/display.texi (Text Display): Document display of glyphless
 characters.
 doc/lispref/display.texi (Usual Display): Characters with no fonts are not
 necessarily displayed as empty boxes.
 etc/NEWS: Document display of glyphless characters.

6 files changed, 73 insertions, 12 deletions

diff --git a/doc/emacs/ChangeLog b/doc/emacs/ChangeLog
index e96846d7ea2..cb243825d5d 100644
--- a/doc/emacs/ChangeLog
+++ b/doc/emacs/ChangeLog
@@ -1,3 +1,14 @@
+2010-11-13  Eli Zaretskii  <eliz@gnu.org>
+
+        * rmail.texi (Rmail Coding): Characters with no fonts are not
+        necessarily displayed as empty boxes.
+
+        * mule.texi (Language Environments, Fontsets): Characters with no
+        fonts are not necessarily displayed as empty boxes.
+
+        * display.texi (Text Display): Document display of glyphless
+        characters.
+
 2010-11-13  Glenn Morris  <rgm@gnu.org>
 
         * basic.texi (Position Info): Add M-x count-words-region.
diff --git a/doc/emacs/display.texi b/doc/emacs/display.texi
index 3b5e7b0b955..cd08a524f50 100644
--- a/doc/emacs/display.texi
+++ b/doc/emacs/display.texi
@@ -1136,6 +1136,48 @@ prefix these characters with an escape character.
 by means of a display table.  @xref{Display Tables,, Display Tables,
 elisp, The Emacs Lisp Reference Manual}.
 
+@cindex glyphless characters
+@cindex characters with no font glyphs
+  On graphics displays, some characters could have no glyphs in any of
+the fonts available to Emacs.  On text terminals, some characters
+could be impossible to encode with the terminal coding system
+(@pxref{Terminal Coding}).  Emacs can display such @dfn{glyphless}
+characters using one of the following methods:
+
+@table @code
+@item zero-width
+Don't display the character.
+
+@item thin-space
+Display a thin space, 1-pixel wide on graphics displays or 1-character
+wide on text terminals.
+
+@item empty-box
+Display an empty box.
+
+@item acronym
+Display the acronym of the character's name (such as @sc{zwnj} or
+@sc{rlm}) in a box.
+
+@item hex-code
+Display the Unicode codepoint of the character in hexadecimal
+notation, in a box.
+@end table
+
+@noindent
+@cindex @code{glyphless-char} face
+With the exception of @code{zero-width}, all other methods draw these
+characters in a special face @code{glyphless-char}, which you can
+customize.
+
+@vindex glyphless-char-display-control
+@vindex char-acronym-table
+To control what glyphless characters are displayed using which method,
+customize the variable @code{glyphless-char-display-control}; see its
+doc string for the details.  For even finer control, set the elements
+of 2 char-tables: @code{glyphless-char-display} and
+@code{char-acronym-table}.
+
 @node Cursor Display
 @section Displaying the Cursor
 
diff --git a/doc/emacs/mule.texi b/doc/emacs/mule.texi
index 9fdef175826..79dbf78f292 100644
--- a/doc/emacs/mule.texi
+++ b/doc/emacs/mule.texi
@@ -351,10 +351,11 @@ which prefers Cyrillic characters and files encoded in Windows-1255).
 @cindex Intlfonts package, installation
   To display the script(s) used by your language environment on a
 graphical display, you need to have a suitable font.  If some of the
-characters appear as empty boxes, you should install the GNU Intlfonts
-package, which includes fonts for most supported scripts.@footnote{If
-you run Emacs on X, you need to inform the X server about the location
-of the newly installed fonts with the following commands:
+characters appear as empty boxes or hex codes, you should install the
+GNU Intlfonts package, which includes fonts for most supported
+scripts.@footnote{If you run Emacs on X, you need to inform the X
+server about the location of the newly installed fonts with the
+following commands:
 
 @example
  xset fp+ /usr/local/share/emacs/fonts
@@ -1314,10 +1315,11 @@ characters the font does not cover.  The standard fontset is only used if
 explicitly requested, despite its name.
 
   A fontset does not necessarily specify a font for every character
-code.  If a fontset specifies no font for a certain character, or if it
-specifies a font that does not exist on your system, then it cannot
-display that character properly.  It will display that character as an
-empty box instead.
+code.  If a fontset specifies no font for a certain character, or if
+it specifies a font that does not exist on your system, then it cannot
+display that character properly.  It will display that character as a
+hex code or thin space or an empty box instead.  (@xref{Text Display,
+glyphless characters}, for details.)
 
 @node Defining Fontsets
 @section Defining fontsets
diff --git a/doc/emacs/rmail.texi b/doc/emacs/rmail.texi
index d477ca73c46..ddf68e62bbf 100644
--- a/doc/emacs/rmail.texi
+++ b/doc/emacs/rmail.texi
@@ -1192,7 +1192,8 @@ specification, or because the specification was inaccurate.  For
 example, a misconfigured mailer could send a message with a
 @samp{charset=iso-8859-1} header when the message is actually encoded
 in @code{koi8-r}.  When you see the message text garbled, or some of
-its characters displayed as empty boxes, this may have happened.
+its characters displayed as hex codes or empty boxes, this may have
+happened.
 
 @findex rmail-redecode-body
   You can correct the problem by decoding the message again using the
diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index 5607d179aad..d6853e0066d 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,3 +1,8 @@
+2010-11-13  Eli Zaretskii  <eliz@gnu.org>
+
+        * display.texi (Usual Display): Characters with no fonts are not
+        necessarily displayed as empty boxes.
+
 2010-10-31  Glenn Morris  <rgm@gnu.org>
 
         * maps.texi (Standard Keymaps): Update File menu description.
diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index 92f96d302d9..6e872ad4233 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -5579,9 +5579,9 @@ digit characters representing the character code in octal.  (A display
 table can specify a glyph to use instead of @samp{\}.)
 
 @item
-Multibyte character codes above 256 are displayed as themselves, or as a
-question mark or empty box if the terminal cannot display that
-character.
+Multibyte character codes above 256 are displayed as themselves, or as
+a question mark or a hex code or an empty box if the terminal cannot
+display that character.
 @end itemize
 
   The usual display conventions apply even when there is a display