Let people enable font features through fontconfig snippets

Like this:

<match target="font">
  <edit name="pangofontfeatures" mode="append">
    <string>smcp</string>
    <string>ss20</string>
  </edit>
</match>

Finally we are starting to see new features coming out of the HarfBuzz integration...

docs/pango-sections.txt

@@ -915,6 +915,7 @@ pango_fc_font_map_find_decoder
 pango_fc_font_map_cache_clear
 pango_fc_font_map_shutdown
 pango_fc_font_description_from_pattern
+PANGO_FC_FONT_FEATURES
 PANGO_FC_GRAVITY
 PANGO_FC_VERSION
 PANGO_FC_PRGNAME

modules/basic/basic-fc.c

@@ -29,6 +29,7 @@
 
 #include "pango-engine.h"
 #include "pango-utils.h"
+#include "pangofc-fontmap.h"
 #include "pangofc-font.h"
 #include <hb-ft.h>
 #include <hb-glib.h>
@@ -318,6 +319,8 @@ basic_engine_shape (PangoEngineShape    *engine G_GNUC_UNUSED,
   int last_cluster;
   guint i, num_glyphs;
   unsigned int item_offset = item_text - paragraph_text;
+  hb_feature_t features[8];
+  unsigned int num_features = 0;
 
   g_return_if_fail (font != NULL);
   g_return_if_fail (analysis != NULL);
@@ -367,7 +370,26 @@ basic_engine_shape (PangoEngineShape    *engine G_GNUC_UNUSED,
 		       (item_offset + item_length == paragraph_length ? HB_BUFFER_FLAG_EOT : 0));
 
   hb_buffer_add_utf8 (hb_buffer, paragraph_text, paragraph_length, item_offset, item_length);
-  hb_shape (hb_font, hb_buffer, NULL, 0);
+
+  /* Setup features from fontconfig pattern. */
+  if (fc_font->font_pattern)
+    {
+      char *s;
+      while (num_features < G_N_ELEMENTS (features) &&
+	     FcResultMatch == FcPatternGetString (fc_font->font_pattern,
+						  PANGO_FC_FONT_FEATURES,
+						  num_features,
+						  (FcChar8 **) &s))
+	{
+	  features[num_features].tag   = hb_tag_from_string (s, -1);
+	  features[num_features].value = 1;
+	  features[num_features].start = 0;
+	  features[num_features].end   = (unsigned int) -1;
+	  num_features++;
+	}
+    }
+
+  hb_shape (hb_font, hb_buffer, features, num_features);
 
   if (PANGO_GRAVITY_IS_IMPROPER (analysis->gravity))
     hb_buffer_reverse (hb_buffer);

pango/pangofc-fontmap.h

@@ -266,6 +266,20 @@ PangoFontDescription *pango_fc_font_description_from_pattern (FcPattern *pattern
  */
 #define PANGO_FC_PRGNAME "pangoprgname"
 
+/**
+ * PANGO_FC_FONT_FEATURES:
+ *
+ * String representing a fontconfig property name that Pango reads from font
+ * patterns to populate list of OpenType features to be enabled for the font
+ * by default.
+ *
+ * The property will have a number of string elements, each of which is the
+ * OpenType feature tag of one feature to enable.
+ *
+ * Since: 1.34
+ */
+#define PANGO_FC_FONT_FEATURES "pangofontfeatures"
+
 G_END_DECLS
 
 #endif /* __PANGO_FC_FONT_MAP_H__ */