[buffer] Add hb_buffer_create_similar()

Fixes https://github.com/harfbuzz/harfbuzz/issues/1555

docs/harfbuzz-sections.txt

@@ -45,6 +45,7 @@ hb_memory_mode_t
 HB_SEGMENT_PROPERTIES_DEFAULT
 HB_BUFFER_REPLACEMENT_CODEPOINT_DEFAULT
 hb_buffer_create
+hb_buffer_create_similar
 hb_buffer_reference
 hb_buffer_get_empty
 hb_buffer_destroy

src/hb-buffer.cc

@@ -104,7 +104,7 @@ hb_segment_properties_hash (const hb_segment_properties_t *p)
  *
  * Since: REPLACEME
  **/
-HB_EXTERN void
+void
 hb_segment_properties_overlay (hb_segment_properties_t *p,
 			       const hb_segment_properties_t *src)
 {
@@ -255,6 +255,18 @@ hb_buffer_t::get_scratch_buffer (unsigned int *size)
 
 /* HarfBuzz-Internal API */
 
+void
+hb_buffer_t::similar (const hb_buffer_t &src)
+{
+  hb_unicode_funcs_destroy (unicode);
+  unicode = hb_unicode_funcs_reference (src.unicode);
+  flags = src.flags;
+  cluster_level = src.cluster_level;
+  replacement = src.invisible;
+  invisible = src.invisible;
+  not_found = src.not_found;
+}
+
 void
 hb_buffer_t::reset ()
 {
@@ -649,6 +661,47 @@ hb_buffer_create ()
   return buffer;
 }
 
+/**
+ * hb_buffer_create_similar:
+ * @src: An #hb_buffer_t
+ *
+ * Resets the buffer to its initial status, as if it was just newly created
+ * with hb_buffer_create().
+ *
+ * Return value: (transfer full):
+ * A newly allocated #hb_buffer_t, similar to hb_buffer_create(). The only
+ * difference is that the buffer is configured similarly to @src.
+ *
+ * Since: REPLACEME
+ **/
+hb_buffer_t *
+hb_buffer_create_similar (const hb_buffer_t *src)
+{
+  hb_buffer_t *buffer = hb_buffer_create ();
+
+  buffer->similar (*src);
+
+  return buffer;
+}
+
+/**
+ * hb_buffer_reset:
+ * @buffer: An #hb_buffer_t
+ *
+ * Resets the buffer to its initial status, as if it was just newly created
+ * with hb_buffer_create().
+ *
+ * Since: 0.9.2
+ **/
+void
+hb_buffer_reset (hb_buffer_t *buffer)
+{
+  if (unlikely (hb_object_is_immutable (buffer)))
+    return;
+
+  buffer->reset ();
+}
+
 /**
  * hb_buffer_get_empty:
  *
@@ -1196,24 +1249,6 @@ hb_buffer_get_not_found_glyph (hb_buffer_t    *buffer)
 }
 
 
-/**
- * hb_buffer_reset:
- * @buffer: An #hb_buffer_t
- *
- * Resets the buffer to its initial status, as if it was just newly created
- * with hb_buffer_create().
- *
- * Since: 0.9.2
- **/
-void
-hb_buffer_reset (hb_buffer_t *buffer)
-{
-  if (unlikely (hb_object_is_immutable (buffer)))
-    return;
-
-  buffer->reset ();
-}
-
 /**
  * hb_buffer_clear_contents:
  * @buffer: An #hb_buffer_t

src/hb-buffer.h

@@ -187,6 +187,13 @@ typedef struct hb_buffer_t hb_buffer_t;
 HB_EXTERN hb_buffer_t *
 hb_buffer_create (void);
 
+HB_EXTERN hb_buffer_t *
+hb_buffer_create_similar (const hb_buffer_t *src);
+
+HB_EXTERN void
+hb_buffer_reset (hb_buffer_t *buffer);
+
+
 HB_EXTERN hb_buffer_t *
 hb_buffer_get_empty (void);
 
@@ -394,8 +401,9 @@ HB_EXTERN hb_codepoint_t
 hb_buffer_get_not_found_glyph (hb_buffer_t    *buffer);
 
 
-HB_EXTERN void
+/*
-hb_buffer_reset (hb_buffer_t *buffer);
+ * Content API.
+ */
 
 HB_EXTERN void
 hb_buffer_clear_contents (hb_buffer_t *buffer);

src/hb-buffer.hh

@@ -201,6 +201,7 @@ struct hb_buffer_t
   hb_glyph_info_t &prev ()      { return out_info[out_len ? out_len - 1 : 0]; }
   hb_glyph_info_t prev () const { return out_info[out_len ? out_len - 1 : 0]; }
 
+  HB_INTERNAL void similar (const hb_buffer_t &src);
   HB_INTERNAL void reset ();
   HB_INTERNAL void clear ();
 

util/shape-options.hh

@@ -60,13 +60,6 @@ struct shape_options_t
     hb_buffer_guess_segment_properties (buffer);
   }
 
-  static void copy_buffer_properties (hb_buffer_t *dst, hb_buffer_t *src)
-  {
-    hb_buffer_set_unicode_funcs (dst, hb_buffer_get_unicode_funcs (src));
-    hb_buffer_set_flags (dst, hb_buffer_get_flags (src));
-    hb_buffer_set_cluster_level (dst, hb_buffer_get_cluster_level (src));
-  }
-
   void populate_buffer (hb_buffer_t *buffer, const char *text, int text_len,
 			const char *text_before, const char *text_after)
   {
@@ -181,10 +174,8 @@ struct shape_options_t
 
     /* Check that breaking up shaping at safe-to-break is indeed safe. */
 
-    hb_buffer_t *fragment = hb_buffer_create ();
+    hb_buffer_t *fragment = hb_buffer_create_similar (buffer);
-    copy_buffer_properties (fragment, buffer);
+    hb_buffer_t *reconstruction = hb_buffer_create_similar (buffer);
-    hb_buffer_t *reconstruction = hb_buffer_create ();
-    copy_buffer_properties (reconstruction, buffer);
 
     unsigned int num_glyphs;
     hb_glyph_info_t *info = hb_buffer_get_glyph_infos (buffer, &num_glyphs);