Turn off ligatures when letterspacing

When letterspacing, we don't want the letters making
up ligatures to 'stick together', so turn off OpenType
features that request optional ligatures (liga, clig,
dlig).

Closes: https://gitlab.gnome.org/GNOME/pango/issues/182

1 files changed, 23 insertions, 0 deletions

diff --git a/pango/pangofc-shape.c b/pango/pangofc-shape.c
index c2b8dc3e..a4fd9a32 100644
--- a/pango/pangofc-shape.c
+++ b/pango/pangofc-shape.c
@@ -110,6 +110,29 @@ apply_extra_attributes (GSList       *attrs,
             }
         }
     }
+
+  /* Turn off ligatures when letterspacing */
+  for (l = attrs; l && *num_features < length; l = l->next)
+    {
+      PangoAttribute *attr = l->data;
+      if (attr->klass->type == PANGO_ATTR_LETTER_SPACING)
+        {
+          hb_tag_t *tags[] = {
+            HB_TAG('l','i','g','a'),
+            HB_TAG('c','l','i','g'),
+            HB_TAG('d','l','i','g'),
+          };
+          int i;
+          for (i = 0; i < G_N_ELEMENTS (tags); i++)
+            {
+              features[*num_features].tag = tags[i];
+              features[*num_features].value = 0;
+              features[*num_features].start = attr->start_index;
+              features[*num_features].end = attr->end_index;
+              (*num_features)++;
+            }
+        }
+    }
 }
 
 typedef struct