Merge pull request #3762 from harfbuzz/safe-to-kashida

Prototype glyph flag safe-to-kashida

src/hb-buffer.h

@@ -142,6 +142,11 @@ typedef struct hb_glyph_info_t {
  *				   shaping, otherwise the buffer flag will not be
  *				   reliably produced.
  * 				   Since: 4.0.0
+ * @HB_GLYPH_FLAG_SAFE_TO_INSERT_TATWEEL: In scripts that use elongation (Arabic,
+				   Mongolian, Syriac, etc.), this flag signifies
+				   that it is safe to insert a U+0640 TATWEEL
+				   character *before* this cluster for elongation.
+				   Since: REPLACEME
  * @HB_GLYPH_FLAG_DEFINED: All the currently defined flags.
  *
  * Flags for #hb_glyph_info_t.
@@ -149,10 +154,11 @@ typedef struct hb_glyph_info_t {
  * Since: 1.5.0
  */
 typedef enum { /*< flags >*/
-  HB_GLYPH_FLAG_UNSAFE_TO_BREAK		= 0x00000001,
-  HB_GLYPH_FLAG_UNSAFE_TO_CONCAT	= 0x00000002,
+  HB_GLYPH_FLAG_UNSAFE_TO_BREAK			= 0x00000001,
+  HB_GLYPH_FLAG_UNSAFE_TO_CONCAT		= 0x00000002,
+  HB_GLYPH_FLAG_SAFE_TO_INSERT_TATWEEL		= 0x00000004,
 
-  HB_GLYPH_FLAG_DEFINED			= 0x00000003 /* OR of all defined flags */
+  HB_GLYPH_FLAG_DEFINED				= 0x00000007 /* OR of all defined flags */
 } hb_glyph_flags_t;
 
 HB_EXTERN hb_glyph_flags_t
@@ -373,6 +379,10 @@ hb_buffer_guess_segment_properties (hb_buffer_t *buffer);
  *                      flag indicating that the @HB_GLYPH_FLAG_UNSAFE_TO_CONCAT
  *                      glyph-flag should be produced by the shaper. By default
  *                      it will not be produced since it incurs a cost. Since: 4.0.0
+ * @HB_BUFFER_FLAG_PRODUCE_SAFE_TO_INSERT_TATWEEL:
+ *                      flag indicating that the @HB_GLYPH_FLAG_SAFE_TO_INSERT_TATWEEL
+ *                      glyph-flag should be produced by the shaper. By default
+ *                      it will not be produced. Since: REPLACEME
  * @HB_BUFFER_FLAG_DEFINED: All currently defined flags: Since: 4.4.0
  *
  * Flags for #hb_buffer_t.
@@ -388,8 +398,9 @@ typedef enum { /*< flags >*/
   HB_BUFFER_FLAG_DO_NOT_INSERT_DOTTED_CIRCLE	= 0x00000010u,
   HB_BUFFER_FLAG_VERIFY				= 0x00000020u,
   HB_BUFFER_FLAG_PRODUCE_UNSAFE_TO_CONCAT	= 0x00000040u,
+  HB_BUFFER_FLAG_PRODUCE_SAFE_TO_INSERT_TATWEEL	= 0x00000070u,
 
-  HB_BUFFER_FLAG_DEFINED			= 0x0000007Fu
+  HB_BUFFER_FLAG_DEFINED			= 0x000000FFu
 } hb_buffer_flags_t;
 
 HB_EXTERN void

src/hb-buffer.hh

@@ -462,6 +462,17 @@ struct hb_buffer_t
 		      start, end,
 		      true);
   }
+  void safe_to_insert_tatweel (unsigned int start = 0, unsigned int end = -1)
+  {
+    if ((flags & HB_BUFFER_FLAG_PRODUCE_SAFE_TO_INSERT_TATWEEL) == 0)
+    {
+      unsafe_to_break (start, end);
+      return;
+    }
+    _set_glyph_flags (HB_GLYPH_FLAG_SAFE_TO_INSERT_TATWEEL,
+		      start, end,
+		      true);
+  }
   void unsafe_to_concat (unsigned int start = 0, unsigned int end = -1)
   {
     if (likely ((flags & HB_BUFFER_FLAG_PRODUCE_UNSAFE_TO_CONCAT) == 0))

src/hb-ot-shape.cc

@@ -1141,6 +1141,16 @@ hb_propagate_flags (hb_buffer_t *buffer)
   if (!(buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_HAS_GLYPH_FLAGS))
     return;
 
+  /* If we are producing SAFE_TO_INSERT_TATWEEL, then do two things:
+   *
+   * - If the places that the Arabic shaper marked as SAFE_TO_INSERT_TATWEEL,
+   *   are UNSAFE_TO_BREAK, then clear the SAFE_TO_INSERT_TATWEEL,
+   * - Any place that is SAFE_TO_INSERT_TATWEEL, is also now UNSAFE_TO_BREAK.
+   *
+   * We couldn't make this interaction earlier. It has to be done here.
+   */
+  bool flip_tatweel = buffer->flags & HB_BUFFER_FLAG_PRODUCE_SAFE_TO_INSERT_TATWEEL;
+
   hb_glyph_info_t *info = buffer->info;
 
   foreach_cluster (buffer, start, end)
@@ -1148,9 +1158,18 @@ hb_propagate_flags (hb_buffer_t *buffer)
     unsigned int mask = 0;
     for (unsigned int i = start; i < end; i++)
       mask |= info[i].mask & HB_GLYPH_FLAG_DEFINED;
+
+    if (flip_tatweel)
+    {
+      if (mask & HB_GLYPH_FLAG_UNSAFE_TO_BREAK)
+	mask &= ~HB_GLYPH_FLAG_SAFE_TO_INSERT_TATWEEL;
+      if (mask & HB_GLYPH_FLAG_SAFE_TO_INSERT_TATWEEL)
+	mask |= HB_GLYPH_FLAG_UNSAFE_TO_BREAK | HB_GLYPH_FLAG_UNSAFE_TO_CONCAT;
+    }
+
     if (mask)
       for (unsigned int i = start; i < end; i++)
-	info[i].mask |= mask;
+	info[i].mask = mask;
   }
 }
 

src/hb-ot-shaper-arabic.cc

@@ -331,7 +331,7 @@ arabic_joining (hb_buffer_t *buffer)
     if (entry->prev_action != NONE && prev != UINT_MAX)
     {
       info[prev].arabic_shaping_action() = entry->prev_action;
-      buffer->unsafe_to_break (prev, i + 1);
+      buffer->safe_to_insert_tatweel (prev, i + 1);
     }
     else
     {
@@ -365,7 +365,7 @@ arabic_joining (hb_buffer_t *buffer)
     if (entry->prev_action != NONE && prev != UINT_MAX)
     {
       info[prev].arabic_shaping_action() = entry->prev_action;
-      buffer->unsafe_to_break (prev, buffer->len);
+      buffer->safe_to_insert_tatweel (prev, buffer->len);
     }
     else if (2 <= state && state <= 5) /* States that have a possible prev_action. */
     {

util/shape-options.hh

@@ -53,6 +53,7 @@ struct shape_options_t
 				  (eot ? HB_BUFFER_FLAG_EOT : 0) |
 				  (verify ? HB_BUFFER_FLAG_VERIFY : 0) |
 				  (unsafe_to_concat ? HB_BUFFER_FLAG_PRODUCE_UNSAFE_TO_CONCAT : 0) |
+				  (safe_to_insert_tatweel ? HB_BUFFER_FLAG_PRODUCE_SAFE_TO_INSERT_TATWEEL : 0) |
 				  (preserve_default_ignorables ? HB_BUFFER_FLAG_PRESERVE_DEFAULT_IGNORABLES : 0) |
 				  (remove_default_ignorables ? HB_BUFFER_FLAG_REMOVE_DEFAULT_IGNORABLES : 0) |
 				  0));
@@ -139,6 +140,7 @@ struct shape_options_t
   hb_bool_t normalize_glyphs = false;
   hb_bool_t verify = false;
   hb_bool_t unsafe_to_concat = false;
+  hb_bool_t safe_to_insert_tatweel = false;
   unsigned int num_iterations = 1;
 };
 
@@ -263,6 +265,7 @@ shape_options_t::add_options (option_parser_t *parser)
     {"cluster-level",	0, 0, G_OPTION_ARG_INT,		&this->cluster_level,		"Cluster merging level (default: 0)",	"0/1/2"},
     {"normalize-glyphs",0, 0, G_OPTION_ARG_NONE,	&this->normalize_glyphs,	"Rearrange glyph clusters in nominal order",	nullptr},
     {"unsafe-to-concat",0, 0, G_OPTION_ARG_NONE,	&this->unsafe_to_concat,	"Produce unsafe-to-concat glyph flag",	nullptr},
+    {"safe-to-insert-tatweel",0, 0, G_OPTION_ARG_NONE,	&this->safe_to_insert_tatweel,	"Produce safe-to-insert-tatweel glyph flag",	nullptr},
     {"verify",		0, 0, G_OPTION_ARG_NONE,	&this->verify,			"Perform sanity checks on shaping results",	nullptr},
     {"num-iterations", 'n', G_OPTION_FLAG_IN_MAIN,
 			      G_OPTION_ARG_INT,		&this->num_iterations,		"Run shaper N times (default: 1)",	"N"},