Add a function to update attribute lists

Add a function that can update positions of
attributes as the underlying text is changing.

This is meant to be used to update an attribute
list as text transformations are applied, like
capitalization.

3 files changed, 48 insertions, 0 deletions

diff --git a/docs/pango-sections.txt b/docs/pango-sections.txt
index 9bf20619..60d360d6 100644
--- a/docs/pango-sections.txt
+++ b/docs/pango-sections.txt
@@ -410,6 +410,7 @@ pango_attr_list_insert_before
 pango_attr_list_change
 pango_attr_list_splice
 pango_attr_list_filter
+pango_attr_list_apply_delta
 PangoAttrFilterFunc
 pango_attr_list_get_iterator
 PangoAttrIterator
diff --git a/pango/pango-attributes.c b/pango/pango-attributes.c
index 85e5a240..f641e9ac 100644
--- a/pango/pango-attributes.c
+++ b/pango/pango-attributes.c
@@ -1599,6 +1599,48 @@ pango_attr_list_change (PangoAttrList  *list,
 }
 
 /**
+ * pango_attr_list_apply_delta:
+ * @list: a #PangoAttrList
+ * @pos: the position of the change
+ * @remove: the number of removed bytes
+ * @add: the number of added bytes
+ *
+ * Update indices of attributes in @list for
+ * a change in the text they refer to.
+ *
+ * The change that this function applies is
+ * removing @remove bytes at position @pos
+ * and inserting @add bytes instead.
+ *
+ * Attributes start and end positions are updated
+ * if they are behind @pos + @remove. Positions
+ * that fall into the (@pos, @pos + @remove) range
+ * are not updated, since we don't know how the
+ * removed and added text affects them.
+ */
+void
+pango_attr_list_apply_delta (PangoAttrList *list,
+                             int             pos,
+                             int             remove,
+                             int             add)
+{
+  GSList *l;
+
+  for (l = list->attributes; l; l = l->next)
+    {
+      PangoAttribute *attr = l->data;
+
+      if (attr->end_index < pos)
+        continue;
+
+      if (attr->start_index >= pos + remove)
+        attr->start_index += add - remove;
+      if (attr->end_index >= pos + remove)
+        attr->end_index += add - remove;
+    }
+}
+
+/**
  * pango_attr_list_splice:
  * @list: a #PangoAttrList
  * @other: another #PangoAttrList
diff --git a/pango/pango-attributes.h b/pango/pango-attributes.h
index cff495b2..b933bc11 100644
--- a/pango/pango-attributes.h
+++ b/pango/pango-attributes.h
@@ -547,6 +547,11 @@ void               pango_attr_list_splice        (PangoAttrList  *list,
 						  PangoAttrList  *other,
 						  gint            pos,
 						  gint            len);
+PANGO_AVAILABLE_IN_1_44
+void               pango_attr_list_apply_delta   (PangoAttrList  *list,
+                                                  int             pos,
+                                                  int             remove,
+                                                  int             add);
 
 PANGO_AVAILABLE_IN_1_2
 PangoAttrList *pango_attr_list_filter (PangoAttrList       *list,