Re: Line wrap reconsidered

[Yuan Fu <casouri@gmail.com>]

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I finally figured it out. The problem seems to be the use of the macro IT_CHAR_HAS_CATEGORY, which is modeled after IT_DISPLAYING_WHITESPACE. IT_CHAR_HAS_CATEGORY uses a series of ||. I changed it to a function that uses if … else if … else (which IMO should be the correct way to implement it anyway), and the problem went away.

Please have a look at the patch and see if it’s ok. If you think it’s good I can then update NEWS and the manual and submit a bug report. wrap.txt is the file I used to test word wrapping. To enable the full feature, set cjk-word-wrap to t and load kinsoku.el.

Yuan


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From 5df09de567796f62472c601afe92df5179f54911 Mon Sep 17 00:00:00 2001
From: Yuan Fu <casouri@gmail.com>
Date: Tue, 26 May 2020 22:47:27 -0400
Subject: [PATCH] Improve word wrapping for CJK characters

* src/xdisp.c (it_char_has_category, char_can_wrap_before,
char_can_wrap_after): New function.
(move_it_in_display_line_to, display_line): Replace
IT_DISPLAYING_WHITESPACE with char_can_wrap_before and
char_can_wrap_after.
(cjk-word-wrap): New variable.
---
 src/xdisp.c | 169 ++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 130 insertions(+), 39 deletions(-)

diff --git a/src/xdisp.c b/src/xdisp.c
index cf15f579b5..3372a8aaa5 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -447,6 +447,7 @@ Copyright (C) 1985-1988, 1993-1995, 1997-2020 Free Software Foundation,
 #include "termchar.h"
 #include "dispextern.h"
 #include "character.h"
+#include "category.h"
 #include "buffer.h"
 #include "charset.h"
 #include "indent.h"
@@ -508,6 +509,69 @@ #define IT_DISPLAYING_WHITESPACE(it)					\
 	   && (*BYTE_POS_ADDR (IT_BYTEPOS (*it)) == ' '			\
 	       || *BYTE_POS_ADDR (IT_BYTEPOS (*it)) == '\t'))))
 
+/* These are the category sets we use.  */
+#define NOT_AT_EOL 60 /* < */
+#define NOT_AT_BOL 62 /* > */
+#define LINE_BREAKABLE 124 /* | */
+
+static bool it_char_has_category(struct it *it, int cat)
+{
+  if (it->what == IT_CHARACTER)
+    return CHAR_HAS_CATEGORY (it->c, cat);
+  else if (STRINGP (it->string))
+    return CHAR_HAS_CATEGORY (SREF (it->string,
+                                    IT_STRING_BYTEPOS (*it)), cat);
+  else if (it->s)
+    return CHAR_HAS_CATEGORY (it->s[IT_BYTEPOS (*it)], cat);
+  else if (IT_BYTEPOS (*it) < ZV_BYTE)
+    return CHAR_HAS_CATEGORY (*BYTE_POS_ADDR (IT_BYTEPOS (*it)), cat);
+  else
+    return false;
+}
+
+/* Return true if the current character allows wrapping before it.   */
+static bool char_can_wrap_before (struct it *it)
+{
+  if (!Vcjk_word_wrap)
+    return !IT_DISPLAYING_WHITESPACE (it);
+
+  /* For CJK (LTR) text in RTL paragraph, EOL and BOL are flipped.  */
+  int not_at_bol;
+  if (it->glyph_row && it->glyph_row->reversed_p)
+    not_at_bol = NOT_AT_EOL;
+  else
+    not_at_bol = NOT_AT_BOL;
+  /* You cannot wrap before a space or tab because that way you'll
+     have space and tab at the beginning of next line.  */
+  return (!IT_DISPLAYING_WHITESPACE (it)
+          // Can be at BOL.
+          && !it_char_has_category (it, not_at_bol));
+}
+
+/* Return true if the current character allows wrapping after it.   */
+static bool char_can_wrap_after (struct it *it)
+{
+  if (!Vcjk_word_wrap)
+    return IT_DISPLAYING_WHITESPACE (it);
+
+  /* For CJK (LTR) text in RTL paragraph, EOL and BOL are flipped.  */
+  int not_at_eol;
+  if (it->glyph_row && it->glyph_row->reversed_p)
+    not_at_eol = NOT_AT_BOL;
+  else
+    not_at_eol = NOT_AT_EOL;
+
+  return (IT_DISPLAYING_WHITESPACE (it)
+          // Can break after && can be at EOL.
+            || (it_char_has_category (it, LINE_BREAKABLE)
+                && !it_char_has_category (it, not_at_eol)));
+}
+
+#undef IT_DISPLAYING_WHITESPACE
+#undef NOT_AT_EOL
+#undef NOT_AT_BOL
+#undef LINE_BREAKABLE
+
 /* If all the conditions needed to print the fill column indicator are
    met, return the (nonnegative) column number, else return a negative
    value.  */
@@ -9185,13 +9249,14 @@ #define IT_RESET_X_ASCENT_DESCENT(IT)			\
 	{
 	  if (it->line_wrap == WORD_WRAP && it->area == TEXT_AREA)
 	    {
-	      if (IT_DISPLAYING_WHITESPACE (it))
-		may_wrap = true;
-	      else if (may_wrap)
+              /* Can we wrap here? */
+	      if (may_wrap && char_can_wrap_before (it))
 		{
 		  /* We have reached a glyph that follows one or more
-		     whitespace characters.  If the position is
-		     already found, we are done.  */
+		     whitespace characters or a character that allows
+		     wrapping after it.  If this character allows
+		     wrapping before it, save this position as a
+		     wrapping point.  */
 		  if (atpos_it.sp >= 0)
 		    {
 		      RESTORE_IT (it, &atpos_it, atpos_data);
@@ -9206,8 +9271,17 @@ #define IT_RESET_X_ASCENT_DESCENT(IT)			\
 		    }
 		  /* Otherwise, we can wrap here.  */
 		  SAVE_IT (wrap_it, *it, wrap_data);
-		  may_wrap = false;
 		}
+	      /* This has to run after the previous block because the
+		 previous block consumes `may_wrap' and this block
+		 sets it, but the value set by this block is intended
+		 for the _next_ character/iteration.  */
+	      if (char_can_wrap_after (it))
+		/* may_wrap basically means "previous char allows
+		   wrapping after it".  */
+		may_wrap = true;
+	      else
+		may_wrap = false;
 	    }
 	}
 
@@ -9335,10 +9409,10 @@ #define IT_RESET_X_ASCENT_DESCENT(IT)			\
 			    {
 			      bool can_wrap = true;
 
-			      /* If we are at a whitespace character
-				 that barely fits on this screen line,
-				 but the next character is also
-				 whitespace, we cannot wrap here.  */
+			      /* If the previous character says we can
+                                 wrap after it, but the current
+                                 character says we can't wrap before
+                                 it, then we can't wrap here.  */
 			      if (it->line_wrap == WORD_WRAP
 				  && wrap_it.sp >= 0
 				  && may_wrap
@@ -9350,7 +9424,7 @@ #define IT_RESET_X_ASCENT_DESCENT(IT)			\
 				  SAVE_IT (tem_it, *it, tem_data);
 				  set_iterator_to_next (it, true);
 				  if (get_next_display_element (it)
-				      && IT_DISPLAYING_WHITESPACE (it))
+				      && !char_can_wrap_before (it))
 				    can_wrap = false;
 				  RESTORE_IT (it, &tem_it, tem_data);
 				}
@@ -9429,19 +9503,18 @@ #define IT_RESET_X_ASCENT_DESCENT(IT)			\
 		  else
 		    IT_RESET_X_ASCENT_DESCENT (it);
 
-		  /* If the screen line ends with whitespace, and we
-		     are under word-wrap, don't use wrap_it: it is no
-		     longer relevant, but we won't have an opportunity
-		     to update it, since we are done with this screen
-		     line.  */
+		  /* If the screen line ends with whitespace (or
+		     wrap-able character), and we are under word-wrap,
+		     don't use wrap_it: it is no longer relevant, but
+		     we won't have an opportunity to update it, since
+		     we are done with this screen line.  */
 		  if (may_wrap && IT_OVERFLOW_NEWLINE_INTO_FRINGE (it)
 		      /* If the character after the one which set the
-			 may_wrap flag is also whitespace, we can't
-			 wrap here, since the screen line cannot be
-			 wrapped in the middle of whitespace.
-			 Therefore, wrap_it _is_ relevant in that
-			 case.  */
-		      && !(moved_forward && IT_DISPLAYING_WHITESPACE (it)))
+			 may_wrap flag says we can't wrap before it,
+			 we can't wrap here.  Therefore, wrap_it
+			 (previously found wrap-point) _is_ relevant
+			 in that case.  */
+		      && !(moved_forward && char_can_wrap_before (it)))
 		    {
 		      /* If we've found TO_X, go back there, as we now
 			 know the last word fits on this screen line.  */
@@ -23292,9 +23365,8 @@ #define RECORD_MAX_MIN_POS(IT)					\
 
 	  if (it->line_wrap == WORD_WRAP && it->area == TEXT_AREA)
 	    {
-	      if (IT_DISPLAYING_WHITESPACE (it))
-		may_wrap = true;
-	      else if (may_wrap)
+              /* Can we wrap here? */
+	      if (may_wrap && char_can_wrap_before (it))
 		{
 		  SAVE_IT (wrap_it, *it, wrap_data);
 		  wrap_x = x;
@@ -23308,9 +23380,13 @@ #define RECORD_MAX_MIN_POS(IT)					\
 		  wrap_row_min_bpos = min_bpos;
 		  wrap_row_max_pos = max_pos;
 		  wrap_row_max_bpos = max_bpos;
-		  may_wrap = false;
 		}
-	    }
+              /* This has to run after the previous block.  */
+	      if (char_can_wrap_after (it))
+		may_wrap = true;
+              else
+                may_wrap = false;
+            }
 	}
 
       PRODUCE_GLYPHS (it);
@@ -23433,14 +23509,18 @@ #define RECORD_MAX_MIN_POS(IT)					\
 			  /* If line-wrap is on, check if a previous
 			     wrap point was found.  */
 			  if (!IT_OVERFLOW_NEWLINE_INTO_FRINGE (it)
-			      && wrap_row_used > 0
+			      && wrap_row_used > 0 /* Found.  */
 			      /* Even if there is a previous wrap
 				 point, continue the line here as
 				 usual, if (i) the previous character
-				 was a space or tab AND (ii) the
-				 current character is not.  */
-			      && (!may_wrap
-				  || IT_DISPLAYING_WHITESPACE (it)))
+				 allows wrapping after it, AND (ii)
+				 the current character allows wrapping
+				 before it.  Because this is a valid
+				 break point, we can just continue to
+				 the next line at here, there is no
+				 need to wrap early at the previous
+				 wrap point.  */
+			      && (!may_wrap || !char_can_wrap_before (it)))
 			    goto back_to_wrap;
 
 			  /* Record the maximum and minimum buffer
@@ -23468,13 +23548,16 @@ #define RECORD_MAX_MIN_POS(IT)					\
 			      /* If line-wrap is on, check if a
 				 previous wrap point was found.  */
 			      else if (wrap_row_used > 0
-				       /* Even if there is a previous wrap
-					  point, continue the line here as
-					  usual, if (i) the previous character
-					  was a space or tab AND (ii) the
-					  current character is not.  */
-				       && (!may_wrap
-					   || IT_DISPLAYING_WHITESPACE (it)))
+				       /* Even if there is a previous
+					  wrap point, continue the
+					  line here as usual, if (i)
+					  the previous character was a
+					  space or tab AND (ii) the
+					  current character is not,
+					  AND (iii) the current
+					  character allows wrapping
+					  before it.  */
+				       && (!may_wrap || !char_can_wrap_before (it)))
 				goto back_to_wrap;
 
 			    }
@@ -34594,6 +34677,14 @@ syms_of_xdisp (void)
 If `word-wrap' is enabled, you might want to reduce this.  */);
   Vtruncate_partial_width_windows = make_fixnum (50);
 
+  DEFVAR_BOOL("cjk-word-wrap", Vcjk_word_wrap,
+    doc: /*  Non-nil means wrap after CJK chracters.
+Normally when word-wrappping is on, Emacs only breaks line after
+whitespace chracters.  When this option is turned on, Emacs also
+breaks line after CJK characters.  If kinsoku.el is loaded, Emacs also
+respects kinsoku when breaking lines.  */);
+  Vcjk_word_wrap = false;
+
   DEFVAR_LISP ("line-number-display-limit", Vline_number_display_limit,
     doc: /* Maximum buffer size for which line number should be displayed.
 If the buffer is bigger than this, the line number does not appear
-- 
2.27.0


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الثعلب البني السريع يقفز فوق الكلب الكسول.الثعلب البني السريع يقفز فوق الكلب الكسول.الثعلب البني السريع يقز فوق ال 《الكسو  ل.الثعل 》 ب الكسول.الثعلب البني السريع يقفز

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中文中文中文中文中文中文中文中文中文中文中文中文中文中文，中文《中文中文》中文中文中文中文中文中中文中文中文中文中中文中文中文中文中文

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אבגד הוזחטיכך למנן 我今天看了本书，感觉挺有意思，名字是《钢铁是怎样炼成的》

RTL in LRT

我今天看了本书，感觉挺有意思，名字是 הוזחטיכך הוזחטיכך הוזחטיכך《אבג דהוזחטיכך הוזחטיכך למנן》 הוזחטיכך הוזחטיכך הוזחטיכך

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