st: Add support for font-feature-settings

Cantarell now supports tabular figures, which are useful in places
where digits should either align or not use different widths. In
order to allow elements to request the feature, add support for
the corresponding CSS property[0].

[0] https://www.w3.org/TR/css-fonts-3/#font-rend-desc

https://gitlab.gnome.org/GNOME/gnome-shell/issues/34

src/st/st-private.c

@@ -117,6 +117,7 @@ _st_set_text_from_style (ClutterText *text,
   const PangoFontDescription *font;
   StTextAlign align;
   gdouble spacing;
+  gchar *font_features;
 
   st_theme_node_get_foreground_color (theme_node, &color);
   clutter_text_set_color (text, &color);
@@ -151,6 +152,13 @@ _st_set_text_from_style (ClutterText *text,
       pango_attr_list_insert (attribs, letter_spacing);
     }
 
+  font_features = st_theme_node_get_font_features (theme_node);
+  if (font_features)
+    {
+      pango_attr_list_insert (attribs, pango_attr_font_features_new (font_features));
+      g_free (font_features);
+    }
+
   clutter_text_set_attributes (text, attribs);
 
   if (attribs)

src/st/st-theme-node.c

@@ -3019,6 +3019,39 @@ st_theme_node_get_font (StThemeNode *node)
   return node->font_desc;
 }
 
+gchar *
+st_theme_node_get_font_features (StThemeNode *node)
+{
+  int i;
+
+  ensure_properties (node);
+
+  for (i = node->n_properties - 1; i >= 0; i--)
+    {
+      CRDeclaration *decl = node->properties[i];
+
+      if (strcmp (decl->property->stryng->str, "font-feature-settings") == 0)
+        {
+          CRTerm *term = decl->value;
+
+          if (!term->next && term->type == TERM_IDENT)
+            {
+              gchar *ident = term->content.str->stryng->str;
+
+              if (strcmp (ident, "inherit") == 0)
+                break;
+
+              if (strcmp (ident, "normal") == 0)
+                return NULL;
+            }
+
+          return (gchar *)cr_term_to_string (term);
+        }
+    }
+
+  return node->parent_node ? st_theme_node_get_font_features (node->parent_node) : NULL;
+}
+
 /**
  * st_theme_node_get_border_image:
  * @node: a #StThemeNode

src/st/st-theme-node.h

@@ -232,6 +232,8 @@ double st_theme_node_get_letter_spacing (StThemeNode *node);
  */
 const PangoFontDescription *st_theme_node_get_font (StThemeNode *node);
 
+gchar *st_theme_node_get_font_features (StThemeNode *node);
+
 StBorderImage *st_theme_node_get_border_image (StThemeNode *node);
 StShadow      *st_theme_node_get_box_shadow   (StThemeNode *node);
 StShadow      *st_theme_node_get_text_shadow  (StThemeNode *node);

src/st/test-theme.c

@@ -59,6 +59,24 @@ assert_font (StThemeNode *node,
   g_free (value);
 }
 
+static void
+assert_font_features (StThemeNode *node,
+                      const char  *node_description,
+                      const char  *expected)
+{
+  char *value = st_theme_node_get_font_features (node);
+
+  if (g_strcmp0 (expected, value) != 0)
+    {
+      g_print ("%s: %s.font-feature-settings: expected: %s, got: %s\n",
+               test, node_description, expected, value);
+      fail = TRUE;
+    }
+
+  if (value)
+    g_free (value);
+}
+
 static char *
 text_decoration_to_string (StTextDecoration decoration)
 {
@@ -413,6 +431,22 @@ test_font (void)
   assert_font (text3,  "text3",  "serif Bold Oblique Small-Caps 24px");
 }
 
+static void
+test_font_features (void)
+{
+  test = "font_features";
+  /* group1 has font-feature-settings: "tnum" */
+  assert_font_features (group1, "group1", "\"tnum\"");
+  /* text2 should inherit from group1 */
+  assert_font_features (text2,  "text2", "\"tnum\"");
+  /* group2 has font-feature-settings: "tnum", "zero" */
+  assert_font_features (group2, "group2", "\"tnum\", \"zero\"");
+  /* text3 should inherit from group2 using the inherit keyword */
+  assert_font_features (text3,  "text3",  "\"tnum\", \"zero\"");
+  /* text4 has font-feature-settings: normal */
+  assert_font_features (text4,  "text4",  NULL);
+}
+
 static void
 test_pseudo_class (void)
 {
@@ -554,6 +588,7 @@ main (int argc, char **argv)
   test_border ();
   test_background ();
   test_font ();
+  test_font_features ();
   test_pseudo_class ();
   test_inline_style ();
 

src/st/test-theme.css

@@ -13,6 +13,8 @@ stage {
     margin-left: 1in;
 
     background: #ff0000 url('some-background.png');
+
+    font-feature-settings: "tnum";
 }
 
 #text1 {
@@ -35,6 +37,7 @@ ClutterTexture.special-text {
 
 #group2 {
     font: italic 12px serif;
+    font-feature-settings: "tnum", "zero";
 }
 
 #text3 {
@@ -42,6 +45,11 @@ ClutterTexture.special-text {
     font-weight: bold;
     font-style: oblique;
     font-size: 200%;
+    font-feature-settings: "pnum";
+}
+
+#text4 {
+    font-feature-settings: normal;
 }
 
 ClutterTexture {
@@ -60,6 +68,10 @@ stage > #text2 {
     color: #ff0000;
 }
 
+#group2 > #text3 {
+    font-feature-settings: inherit;
+}
+
 #group2 {
     background-image: url('other-background.png');
     padding: 1px 2px 3px 4px;