[pango/small-caps: 11/11] itemize: Emulate other casing variants

[Matthias Clasen <matthiasc src gnome org>]

commit 3a2221375542e1f9a0e388a4d3efda20ae440586
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Nov 6 23:53:51 2021 -0400

    itemize: Emulate other casing variants
    
    When we detect that one of the other casing variants
    is requested, but not available via OpenType font
    features, emulate it by splitting the item into
    lowercase and uppercase runs and apply a suitable
    font scale and text transform to the runs to get
    the desired effect.
    
    Still to do: resolve conflics with preexisting
    text transform attributes.

 pango/itemize.c | 195 +++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 131 insertions(+), 64 deletions(-)
---
diff --git a/pango/itemize.c b/pango/itemize.c
index f115abdf..373d8488 100644
--- a/pango/itemize.c
+++ b/pango/itemize.c
@@ -1197,29 +1197,14 @@ apply_font_scale (PangoContext *context,
 }
 
 /* }}} */
-/* {{{ Handling Small Caps */
+/* {{{ Handling Casing variants */
 
 static gboolean
-feature_is_requested (hb_feature_t *features,
-                      guint         num_features,
-                      hb_tag_t      tag)
-{
-  for (guint i = 0; i < num_features; i++)
-    {
-      if (features[i].tag == tag)
-        return features[i].value != 0;
-    }
-
-  return FALSE;
-}
-
-
-static gboolean
-feature_is_supported (hb_font_t           *font,
-                      const PangoAnalysis *analysis,
-                      hb_tag_t             table,
-                      hb_tag_t             feature)
+all_features_supported (PangoItem *item,
+                        hb_tag_t  *features,
+                        guint      n_features)
 {
+  hb_font_t *font = pango_font_get_hb_font (item->analysis.font);
   hb_face_t *face = hb_font_get_face (font);
   hb_script_t script;
   hb_language_t language;
@@ -1229,57 +1214,116 @@ feature_is_supported (hb_font_t           *font,
   guint language_count = HB_OT_MAX_TAGS_PER_LANGUAGE;
   hb_tag_t language_tags[HB_OT_MAX_TAGS_PER_LANGUAGE];
   guint script_index, language_index;
-  guint feature_index;
+  guint index;
 
-  script = g_unicode_script_to_iso15924 (analysis->script);
-  language = hb_language_from_string (pango_language_to_string (analysis->language), -1);
+  script = g_unicode_script_to_iso15924 (item->analysis.script);
+  language = hb_language_from_string (pango_language_to_string (item->analysis.language), -1);
 
   hb_ot_tags_from_script_and_language (script, language,
                                        &script_count, script_tags,
                                        &language_count, language_tags);
-  hb_ot_layout_table_select_script (face, table,
+  hb_ot_layout_table_select_script (face, HB_OT_TAG_GSUB,
                                     script_count, script_tags,
                                     &script_index,
                                     &chosen_script);
-  hb_ot_layout_script_select_language (face, table,
+  hb_ot_layout_script_select_language (face, HB_OT_TAG_GSUB,
                                        script_index,
                                        language_count, language_tags,
                                        &language_index);
 
-  return hb_ot_layout_language_find_feature (face, table,
-                                             script_index, language_index,
-                                             feature,
-                                             &feature_index);
+  for (int i = 0; i < n_features; i++)
+    {
+      if (!hb_ot_layout_language_find_feature (face, HB_OT_TAG_GSUB,
+                                               script_index, language_index,
+                                               features[i],
+                                               &index))
+        return FALSE;
+    }
+
+  return TRUE;
 }
 
 static gboolean
-small_caps_is_requested (PangoItem *item)
+variant_supported (PangoItem    *item,
+                   PangoVariant  variant)
 {
-  hb_feature_t features[32];
-  unsigned int num_features = 0;
+  hb_tag_t features[2];
+  guint num_features = 0;
 
-  pango_analysis_collect_features (&item->analysis,
-                                   features, G_N_ELEMENTS (features),
-                                   &num_features);
+  switch (variant)
+    {
+    case PANGO_VARIANT_NORMAL:
+    case PANGO_VARIANT_UNICASE: /* Can't really emulate these */
+    case PANGO_VARIANT_TITLE_CAPS:
+      return TRUE;
+    case PANGO_VARIANT_SMALL_CAPS:
+      features[num_features++] = HB_TAG ('s', 'm', 'c', 'p');
+      break;
+    case PANGO_VARIANT_ALL_SMALL_CAPS:
+      features[num_features++] = HB_TAG ('s', 'm', 'c', 'p');
+      features[num_features++] = HB_TAG ('c', '2', 's', 'c');
+      break;
+    case PANGO_VARIANT_PETITE_CAPS:
+      features[num_features++] = HB_TAG ('p', 'c', 'a', 'p');
+      break;
+    case PANGO_VARIANT_ALL_PETITE_CAPS:
+      features[num_features++] = HB_TAG ('p', 'c', 'a', 'p');
+      features[num_features++] = HB_TAG ('c', '2', 'p', 'c');
+      break;
+    default:
+      g_assert_not_reached ();
+    }
 
-  return feature_is_requested (features, num_features, HB_TAG ('s', 'm', 'c', 'p'));
+  return all_features_supported (item, features, num_features);
 }
 
-static gboolean
-small_caps_is_supported (PangoItem *item)
+static PangoVariant
+get_font_variant (PangoItem *item)
 {
-  hb_font_t *font = pango_font_get_hb_font (item->analysis.font);
+  PangoFontDescription *desc;
+  PangoVariant variant;
+
+  desc = pango_font_describe (item->analysis.font);
+  variant = pango_font_description_get_variant (desc);
+  pango_font_description_free (desc);
 
-  return feature_is_supported (font, &item->analysis, HB_OT_TAG_GSUB, HB_TAG ('s', 'm', 'c', 'p'));
+  return variant;
 }
 
 static void
-split_item_for_small_caps (const char *text,
-                           GList      *list_item)
+split_item_for_variant (const char   *text,
+                        GList        *list_item,
+                        PangoVariant  variant)
 {
   PangoItem *item = list_item->data;
   const char *start, *end;
   const char *p, *p0;
+  PangoTextTransform transform = PANGO_TEXT_TRANSFORM_NONE;
+  PangoFontScale lowercase_scale = PANGO_FONT_SCALE_NONE;
+  PangoFontScale uppercase_scale = PANGO_FONT_SCALE_NONE;
+
+  switch (variant)
+    {
+    case PANGO_VARIANT_ALL_SMALL_CAPS:
+      uppercase_scale = PANGO_FONT_SCALE_SMALL_CAPS;
+      G_GNUC_FALLTHROUGH;
+    case PANGO_VARIANT_SMALL_CAPS:
+      transform = PANGO_TEXT_TRANSFORM_UPPERCASE;
+      lowercase_scale = PANGO_FONT_SCALE_SMALL_CAPS;
+      break;
+    case PANGO_VARIANT_ALL_PETITE_CAPS:
+      uppercase_scale = PANGO_FONT_SCALE_PETITE_CAPS;
+      G_GNUC_FALLTHROUGH;
+    case PANGO_VARIANT_PETITE_CAPS:
+      transform = PANGO_TEXT_TRANSFORM_UPPERCASE;
+      lowercase_scale = PANGO_FONT_SCALE_PETITE_CAPS;
+      break;
+    case PANGO_VARIANT_NORMAL:
+    case PANGO_VARIANT_UNICASE:
+    case PANGO_VARIANT_TITLE_CAPS:
+    default:
+      g_assert_not_reached ();
+    }
 
   start = text + item->offset;
   end = start + item->length;
@@ -1312,55 +1356,78 @@ split_item_for_small_caps (const char *text,
               new_item = item;
             }
 
-          attr = pango_attr_text_transform_new (PANGO_TEXT_TRANSFORM_UPPERCASE);
-          attr->start_index = new_item->offset;
-          attr->end_index = new_item->offset + new_item->length;
-          new_item->analysis.extra_attrs = g_slist_prepend (new_item->analysis.extra_attrs, attr);
+          if (transform != PANGO_TEXT_TRANSFORM_NONE)
+            {
+              attr = pango_attr_text_transform_new (transform);
+              attr->start_index = new_item->offset;
+              attr->end_index = new_item->offset + new_item->length;
+              new_item->analysis.extra_attrs = g_slist_prepend (new_item->analysis.extra_attrs, attr);
+            }
 
-          attr = pango_attr_font_scale_new (PANGO_FONT_SCALE_SMALL_CAPS);
-          attr->start_index = new_item->offset;
-          attr->end_index = new_item->offset + new_item->length;
-          new_item->analysis.extra_attrs = g_slist_prepend (new_item->analysis.extra_attrs, attr);
+          if (lowercase_scale != PANGO_FONT_SCALE_NONE)
+            {
+              attr = pango_attr_font_scale_new (lowercase_scale);
+              attr->start_index = new_item->offset;
+              attr->end_index = new_item->offset + new_item->length;
+              new_item->analysis.extra_attrs = g_slist_prepend (new_item->analysis.extra_attrs, attr);
+            }
         }
 
       p0 = p;
       while (p < end && !g_unichar_islower (g_utf8_get_char (p)))
         p = g_utf8_next_char (p);
 
-      if (p0 < p && p < end)
+      if (p0 < p)
         {
           PangoItem *new_item;
+          PangoAttribute *attr;
 
           /* p0 .. p is a uppercase segment */
-          new_item = pango_item_split (item, p - p0, g_utf8_strlen (p, p - p0));
-          list_item->data = new_item;
-          list_item = g_list_insert_before (list_item, list_item->next, item);
-          list_item = list_item->next;
+          if (p < end)
+            {
+              new_item = pango_item_split (item, p - p0, g_utf8_strlen (p, p - p0));
+              list_item->data = new_item;
+              list_item = g_list_insert_before (list_item, list_item->next, item);
+              list_item = list_item->next;
+            }
+          else
+            {
+              new_item = item;
+            }
+
+          if (uppercase_scale != PANGO_FONT_SCALE_NONE)
+            {
+              attr = pango_attr_font_scale_new (uppercase_scale);
+              attr->start_index = new_item->offset;
+              attr->end_index = new_item->offset + new_item->length;
+              new_item->analysis.extra_attrs = g_slist_prepend (new_item->analysis.extra_attrs, attr);
+            }
         }
     }
 }
 
 static void
-handle_small_caps_for_item (const char *text,
-                            GList      *l)
+handle_variants_for_item (const char *text,
+                          GList      *l)
 {
   PangoItem *item = l->data;
+  PangoVariant variant;
 
-  if (small_caps_is_requested (item) &&
-      !small_caps_is_supported (item))
-    split_item_for_small_caps (text, l);
+  variant = get_font_variant (item);
+  if (!variant_supported (item, variant))
+    split_item_for_variant (text, l, variant);
 }
 
 static void
-handle_small_caps (const char *text,
-                   GList      *items)
+handle_variants (const char *text,
+                 GList      *items)
 {
   GList *next;
 
   for (GList *l = items; l; l = next)
     {
       next = l->next;
-      handle_small_caps_for_item (text, l);
+      handle_variants_for_item (text, l);
     }
 }
 
@@ -1384,7 +1451,7 @@ post_process_items (PangoContext *context,
       }
   }
 
-  handle_small_caps (text, items);
+  handle_variants (text, items);
 
   /* apply font-scale */
   apply_font_scale (context, items);