Add PangoHbFontmap

This is a fontmap implementation for use with PangoHbFont,
which lets you add individual faces. It handles caching
and lookups and is designed to let subclasses simply provide
a populate vfunc.

Note that the load_fontset implementation here is similar in
style to the one we have in PangoFontMap: for each family
in the font description, pick the best matching face.

5 files changed, 1170 insertions, 0 deletions

diff --git a/pango/meson.build b/pango/meson.build
index 0c6e204a..13bb3a12 100644
--- a/pango/meson.build
+++ b/pango/meson.build
@@ -38,6 +38,7 @@ pango_sources = [
   'pango-hbfamily.c',
   'pango-generic-family.c',
   'pango-hbfont.c',
+  'pango-hbfontmap.c',
 ]
 
 pango_headers = [
@@ -71,6 +72,7 @@ pango_headers = [
   'pango-utils.h',
   'pango-hbface.h',
   'pango-hbfont.h',
+  'pango-hbfontmap.h',
 ]
 
 pango_installed_headers = pango_headers + [ 'pango-version-macros.h' ]
diff --git a/pango/pango-hbfontmap-private.h b/pango/pango-hbfontmap-private.h
new file mode 100644
index 00000000..ec913e9d
--- /dev/null
+++ b/pango/pango-hbfontmap-private.h
@@ -0,0 +1,62 @@
+/* Pango
+ *
+ * Copyright (C) 2021 Matthias Clasen
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#pragma once
+
+#include <pango/pango-hbfontmap.h>
+#include <pango/pango-hbfamily-private.h>
+
+G_BEGIN_DECLS
+
+struct _PangoHbFontMap
+{
+  PangoFontMap parent_instance;
+
+  GPtrArray *added_faces;
+  GPtrArray *added_families;
+  GHashTable *families_hash;
+  GPtrArray *families;
+  GHashTable *fontsets;
+  GQueue fontset_cache;
+
+  double dpi;
+  gboolean in_populate;
+  guint serial;
+};
+
+/**
+ * PangoHbFontMapClass:
+ * @populate: Subclasses should call pango_hb_font_map_add_face to populate
+ *   the map with faces and families in this vfunc.
+ */
+struct _PangoHbFontMapClass
+{
+  PangoFontMapClass parent_class;
+
+  void (* populate) (PangoHbFontMap *self);
+
+  gpointer reserved[10];
+};
+
+PANGO_AVAILABLE_IN_1_52
+void                    pango_hb_font_map_repopulate    (PangoHbFontMap *self,
+                                                         gboolean        add_synthetic);
+
+G_END_DECLS
diff --git a/pango/pango-hbfontmap.c b/pango/pango-hbfontmap.c
new file mode 100644
index 00000000..cfe486bc
--- /dev/null
+++ b/pango/pango-hbfontmap.c
@@ -0,0 +1,1045 @@
+/* Pango
+ *
+ * Copyright (C) 2021 Matthias Clasen
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#include "config.h"
+#include <math.h>
+
+#include <gio/gio.h>
+
+#include "pango-hbfontmap-private.h"
+#include "pango-hbfamily-private.h"
+#include "pango-generic-family-private.h"
+#include "pango-hbface-private.h"
+#include "pango-hbfont-private.h"
+#include "pango-fontset.h"
+#include "pango-trace-private.h"
+#include "pango-context.h"
+
+#include <hb-ot.h>
+
+
+/**
+ * PangoHbFontMap:
+ *
+ * `PangoHbFontMap` is a `PangoFontMap` subclass for use with
+ * `PangoHbFace` and `PangoHbFont`. It handles caching and
+ * lookup of faces and fonts.
+ *
+ * Subclasses populate the fontmap using backend-specific APIs
+ * to enumerate the available fonts on the sytem, but it is
+ * also possible to create an instance of `PangoHbFontMap` and
+ * populate it manually using [method@Pango.HbFontMap.add_file]
+ * and [method@Pango.HbFontMap.add_face].
+ *
+ * Note that to be fully functional, a fontmap needs to provide
+ * generic families for monospace and sans-serif. These can
+ * be added using [method@Pango.HbFontMap.add_family] and
+ * [ctor@Pango.GenericFamily.new].
+ */
+
+
+/* The central api is load_fontset, which takes a font description
+ * and language, finds the matching faces, and creates a PangoFontset
+ * for them. To speed this operation up, the font map maintains a
+ * cache of fontsets (in the form of a GQueue) and has a hash table
+ * for looking up existing fontsets.
+ *
+ * The PangoFontsetCached object is the fontset subclass that is used
+ * here, and it contains the necessary data for the cashing and hashing.
+ * PangoFontsetCached also caches the character-to-font mapping that is
+ * used when itemizing text.
+ */
+
+/* The number of fontsets we keep in the fontset cache */
+
+#define FONTSET_CACHE_SIZE 256
+
+
+/* {{{ GListModel implementation */
+
+static GType
+pango_hb_font_map_get_item_type (GListModel *list)
+{
+  return PANGO_TYPE_FONT_FAMILY;
+}
+
+static guint
+pango_hb_font_map_get_n_items (GListModel *list)
+{
+  PangoHbFontMap *self = PANGO_HB_FONT_MAP (list);
+
+  return self->families->len;
+}
+
+static gpointer
+pango_hb_font_map_get_item (GListModel *list,
+                            guint       position)
+{
+  PangoHbFontMap *self = PANGO_HB_FONT_MAP (list);
+
+  if (position < self->families->len)
+    return g_object_ref (g_ptr_array_index (self->families, position));
+
+  return NULL;
+}
+
+static void
+pango_hb_font_map_list_model_init (GListModelInterface *iface)
+{
+  iface->get_item_type = pango_hb_font_map_get_item_type;
+  iface->get_n_items = pango_hb_font_map_get_n_items;
+  iface->get_item = pango_hb_font_map_get_item;
+}
+
+/* }}} */
+/* {{{ Fontset implementation */
+
+typedef struct _PangoFontsetCached PangoFontsetCached;
+
+struct _PangoFontsetCached
+{
+  PangoFontset parent_instance;
+
+  GPtrArray *items; /* contains PangoHbFont or PangoGenericFamily */
+  PangoLanguage *language;
+  PangoFontDescription *description;
+  float dpi;
+  const PangoMatrix *matrix;
+  GList cache_link;
+  GHashTable *cache;
+};
+
+typedef PangoFontsetClass PangoFontsetCachedClass;
+
+GType pango_fontset_cached_get_type (void) G_GNUC_CONST;
+
+G_DEFINE_TYPE (PangoFontsetCached, pango_fontset_cached, PANGO_TYPE_FONTSET);
+
+static void
+pango_fontset_cached_init (PangoFontsetCached *fontset)
+{
+  fontset->items = g_ptr_array_new_with_free_func (g_object_unref);
+  fontset->cache = g_hash_table_new_full (NULL, NULL, NULL, g_object_unref);
+  fontset->language = NULL;
+}
+
+static void
+pango_fontset_cached_finalize (GObject *object)
+{
+  PangoFontsetCached *self = (PangoFontsetCached *)object;
+
+  g_ptr_array_free (self->items, TRUE);
+  g_hash_table_unref (self->cache);
+  pango_font_description_free (self->description);
+
+  G_OBJECT_CLASS (pango_fontset_cached_parent_class)->finalize (object);
+}
+
+static PangoFont *
+pango_fontset_cached_get_font (PangoFontset *fontset,
+                               guint         wc)
+{
+  PangoFontsetCached *self = (PangoFontsetCached *)fontset;
+  PangoFont *retval;
+  int i;
+
+  retval = g_hash_table_lookup (self->cache, GUINT_TO_POINTER (wc));
+  if (retval)
+    return g_object_ref (retval);
+
+  for (i = 0; i < self->items->len; i++)
+    {
+      gpointer item = g_ptr_array_index (self->items, i);
+
+      if (PANGO_IS_HB_FONT (item))
+        {
+          PangoFont *font = PANGO_FONT (item);
+          if (pango_font_has_char (font, wc))
+            {
+              retval = g_object_ref (font);
+              break;
+            }
+        }
+      else if (PANGO_IS_GENERIC_FAMILY (item))
+        {
+          PangoGenericFamily *family = PANGO_GENERIC_FAMILY (item);
+          PangoHbFace *face;
+
+          /* Here is where we implement delayed picking for generic families.
+           * If a face does not cover the character and its family is generic,
+           * choose a different face from the same family and create a font to use.
+           */
+          face = pango_generic_family_find_face (family,
+                                                 self->description,
+                                                 self->language,
+                                                 wc);
+          if (face)
+            {
+              retval = PANGO_FONT (pango_hb_font_new_for_description (face,
+                                                                      self->description,
+                                                                      self->dpi,
+                                                                      self->matrix));
+              break;
+            }
+        }
+    }
+
+  if (retval)
+    g_hash_table_insert (self->cache, GUINT_TO_POINTER (wc), g_object_ref (retval));
+
+  return retval;
+}
+
+static PangoFont *
+pango_fontset_cached_get_first_font (PangoFontsetCached *self)
+{
+  gpointer item;
+
+  item = g_ptr_array_index (self->items, 0);
+
+  if (PANGO_IS_HB_FONT (item))
+    return g_object_ref (PANGO_FONT (item));
+  else if (PANGO_IS_GENERIC_FAMILY (item))
+    {
+      PangoHbFace *face = pango_generic_family_find_face (PANGO_GENERIC_FAMILY (item), self->description, self->language, 0);
+      return PANGO_FONT (pango_hb_font_new_for_description (face, self->description, self->dpi, self->matrix));
+    }
+
+  return NULL;
+}
+
+static PangoFontMetrics *
+pango_fontset_cached_get_metrics (PangoFontset *fontset)
+{
+  PangoFontsetCached *self = (PangoFontsetCached *)fontset;
+
+  if (self->items->len == 1)
+    {
+      PangoFont *font = pango_fontset_cached_get_first_font (self);
+      PangoFontMetrics *ret;
+
+      ret = pango_font_get_metrics (font, self->language);
+      g_object_unref (font);
+
+      return ret;
+    }
+
+  return PANGO_FONTSET_CLASS (pango_fontset_cached_parent_class)->get_metrics (fontset);
+}
+
+static PangoLanguage *
+pango_fontset_cached_get_language (PangoFontset *fontset)
+{
+  PangoFontsetCached *self = (PangoFontsetCached *)fontset;
+
+  return self->language;
+}
+
+static void
+pango_fontset_cached_foreach (PangoFontset            *fontset,
+                              PangoFontsetForeachFunc  func,
+                              gpointer                 data)
+{
+  PangoFontsetCached *self = (PangoFontsetCached *)fontset;
+  unsigned int i;
+
+  for (i = 0; i < self->items->len; i++)
+    {
+      gpointer item = g_ptr_array_index (self->items, i);
+      PangoFont *font = NULL;
+
+      if (PANGO_IS_HB_FONT (item))
+        font = g_object_ref (PANGO_FONT (item));
+      else if (PANGO_IS_GENERIC_FAMILY (item))
+        {
+          PangoHbFace *face = pango_generic_family_find_face (PANGO_GENERIC_FAMILY (item), self->description, self->language, 0);
+          font = PANGO_FONT (pango_hb_font_new_for_description (face, self->description, self->dpi, self->matrix));
+        }
+
+      if ((*func) (fontset, font, data))
+        {
+          g_object_unref (font);
+          return;
+        }
+      g_object_unref (font);
+    }
+}
+
+static void
+pango_fontset_cached_class_init (PangoFontsetCachedClass *class)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+  PangoFontsetClass *fontset_class = PANGO_FONTSET_CLASS (class);
+
+  object_class->finalize = pango_fontset_cached_finalize;
+
+  fontset_class->get_font = pango_fontset_cached_get_font;
+  fontset_class->get_metrics = pango_fontset_cached_get_metrics;
+  fontset_class->get_language = pango_fontset_cached_get_language;
+  fontset_class->foreach = pango_fontset_cached_foreach;
+}
+
+static PangoFontsetCached *
+pango_fontset_cached_new (const PangoFontDescription *description,
+                          PangoLanguage              *language,
+                          float                       dpi,
+                          const PangoMatrix          *matrix)
+{
+  PangoFontsetCached *self;
+
+  self = g_object_new (pango_fontset_cached_get_type (), NULL);
+  self->language = language;
+  self->description = pango_font_description_copy (description);
+  self->dpi = dpi;
+  self->matrix = matrix;
+
+  return self;
+}
+
+static void
+pango_fontset_cached_add_face (PangoFontsetCached *self,
+                               PangoHbFace        *face)
+{
+  g_ptr_array_add (self->items,
+                   pango_hb_font_new_for_description (face,
+                                                      self->description,
+                                                      self->dpi,
+                                                      self->matrix));
+}
+
+static void
+pango_fontset_cached_add_family (PangoFontsetCached *self,
+                                 PangoGenericFamily *family)
+{
+  g_ptr_array_add (self->items, g_object_ref (family));
+}
+
+static int
+pango_fontset_cached_size (PangoFontsetCached *self)
+{
+  return self->items->len;
+}
+
+#define FNV1_32_INIT ((guint32)0x811c9dc5)
+
+static guint
+pango_fontset_cached_hash (const PangoFontsetCached *fontset)
+{
+  guint32 hash = FNV1_32_INIT;
+
+  return (hash ^
+          GPOINTER_TO_UINT (fontset->language) ^
+          pango_font_description_hash (fontset->description));
+}
+
+static gboolean
+pango_fontset_cached_equal (const PangoFontsetCached *a,
+                            const PangoFontsetCached *b)
+{
+  return a->language == b->language &&
+         pango_font_description_equal (a->description, b->description);
+}
+
+static void
+pango_fontset_cache (PangoFontsetCached *fontset,
+                     PangoHbFontMap     *self)
+{
+  GQueue *cache = &self->fontset_cache;
+  GList *link = &fontset->cache_link;
+
+  if (link->data == fontset)
+    {
+      /* Already in cache, move to head */
+      if (link == cache->head)
+        return;
+
+      g_queue_unlink (cache, link);
+    }
+  else
+    {
+      /* Not in cache yet. Make room... */
+      if (cache->length == FONTSET_CACHE_SIZE)
+        {
+          GList *old = g_queue_pop_tail_link (cache);
+          g_hash_table_remove (self->fontsets, old->data);
+          old->data = NULL;
+        }
+    }
+
+  link->data = fontset;
+  link->prev = NULL;
+  link->next = NULL;
+  g_queue_push_head_link (cache, link);
+}
+
+/* }}} */
+/* {{{ Utilities */
+
+typedef struct {
+  PangoFontFamily family;
+  PangoFontMap *map;
+  const char *name;
+} FamilyKey;
+
+static guint
+pango_family_hash (const FamilyKey *key)
+{
+  const char *p;
+  guint32 h = 5381;
+
+  for (p = (const char *)key->name; *p != '\0'; p++)
+    h = (h << 5) + h + g_ascii_tolower (*p);
+
+  return h;
+}
+
+static gboolean
+pango_family_equal (const FamilyKey *a,
+                    const FamilyKey *b)
+{
+  return g_ascii_strcasecmp (a->name, b->name) == 0;
+}
+
+static PangoFontFamily *
+find_family (PangoHbFontMap *self,
+             const char     *family_name)
+{
+  FamilyKey lookup;
+  PangoFontFamily *family;
+
+  lookup.name = family_name;
+
+  family = PANGO_FONT_FAMILY (g_hash_table_lookup (self->families_hash, &lookup));
+
+  return family;
+}
+
+static void
+clear_caches (PangoHbFontMap *self)
+{
+  g_hash_table_remove_all (self->fontsets);
+  g_queue_init (&self->fontset_cache);
+}
+
+static void
+add_style_variation (PangoHbFamily *family,
+                     PangoHbFace   *face,
+                     PangoStyle     style,
+                     PangoWeight    weight)
+{
+  PangoMatrix italic_matrix = { 1, 0.2, 0, 1, 0, 0 };
+  PangoFontDescription *desc;
+
+  desc = pango_font_description_new ();
+  pango_font_description_set_style (desc, style);
+  pango_font_description_set_weight (desc, weight);
+
+  pango_hb_family_add_face (family,
+      pango_hb_face_new_synthetic (face,
+                                   style == PANGO_STYLE_ITALIC ? &italic_matrix : NULL,
+                                    weight == PANGO_WEIGHT_BOLD,
+                                    NULL,
+                                    desc));
+
+  pango_font_description_free (desc);
+}
+
+static void
+synthesize_bold_and_italic_faces (PangoHbFontMap *map)
+{
+  for (int i = 0; i < map->families->len; i++)
+    {
+      PangoFontFamily *family = g_ptr_array_index (map->families, i);
+      PangoHbFace *regular_face = NULL;
+      int regular_dist = G_MAXINT;
+      int bold_dist = G_MAXINT;
+      gboolean has_italic = FALSE;
+      gboolean has_bold = FALSE;
+      gboolean has_bold_italic = FALSE;
+
+      for (int j = 0; j < g_list_model_get_n_items (G_LIST_MODEL (family)); j++)
+        {
+          PangoHbFace *face = g_list_model_get_item (G_LIST_MODEL (family), j);
+          int weight;
+          PangoStyle style;
+          int dist;
+
+          weight = pango_font_description_get_weight (face->description);
+          style = pango_font_description_get_style (face->description);
+
+          if (style == PANGO_STYLE_NORMAL)
+            {
+              dist = abs (weight - (int)PANGO_WEIGHT_NORMAL);
+
+              if (dist < regular_dist)
+                {
+                  regular_dist = dist;
+                  if (dist < 150)
+                    regular_face = face;
+                }
+
+              dist = abs (weight - (int)PANGO_WEIGHT_BOLD);
+
+              if (dist < bold_dist)
+                {
+                  bold_dist = dist;
+                  has_bold = dist < 150;
+                }
+            }
+          else
+            {
+              if (weight < PANGO_WEIGHT_SEMIBOLD)
+                has_italic = TRUE;
+              else
+                has_bold_italic = TRUE;
+            }
+
+          g_object_unref (face);
+        }
+
+      if (regular_face)
+        {
+          if (!has_italic)
+            add_style_variation (PANGO_HB_FAMILY (family), regular_face, PANGO_STYLE_ITALIC, PANGO_WEIGHT_NORMAL);
+
+          if (!has_bold)
+            add_style_variation (PANGO_HB_FAMILY (family), regular_face, PANGO_STYLE_NORMAL, PANGO_WEIGHT_BOLD);
+
+          if (!has_bold_italic)
+            add_style_variation (PANGO_HB_FAMILY (family), regular_face, PANGO_STYLE_ITALIC, PANGO_WEIGHT_BOLD);
+        }
+    }
+}
+
+ /* }}} */
+/* {{{ PangoFontMap implementation */
+
+G_DEFINE_TYPE_WITH_CODE (PangoHbFontMap, pango_hb_font_map, PANGO_TYPE_FONT_MAP,
+                         G_IMPLEMENT_INTERFACE (G_TYPE_LIST_MODEL, pango_hb_font_map_list_model_init))
+
+
+static void
+pango_hb_font_map_init (PangoHbFontMap *self)
+{
+  self->added_faces = g_ptr_array_new_with_free_func (g_object_unref);
+  self->added_families = g_ptr_array_new_with_free_func (g_object_unref);
+  self->families = g_ptr_array_new_with_free_func (g_object_unref);
+  self->families_hash = g_hash_table_new_full ((GHashFunc) pango_family_hash,
+                                               (GEqualFunc) pango_family_equal,
+                                               NULL,
+                                               NULL);
+  self->fontsets = g_hash_table_new_full ((GHashFunc) pango_fontset_cached_hash,
+                                          (GEqualFunc) pango_fontset_cached_equal,
+                                          NULL,
+                                          (GDestroyNotify) g_object_unref);
+  g_queue_init (&self->fontset_cache);
+  self->dpi = 96.;
+}
+
+static void
+pango_hb_font_map_finalize (GObject *object)
+{
+  PangoHbFontMap *self = PANGO_HB_FONT_MAP (object);
+
+  g_ptr_array_unref (self->added_faces);
+  g_ptr_array_unref (self->added_families);
+  g_hash_table_unref (self->families_hash);
+  g_ptr_array_unref (self->families);
+  g_hash_table_unref (self->fontsets);
+
+  G_OBJECT_CLASS (pango_hb_font_map_parent_class)->finalize (object);
+}
+
+/* Load a font from the first matching family */
+static PangoFont *
+pango_hb_font_map_load_font (PangoFontMap               *map,
+                             PangoContext               *context,
+                             const PangoFontDescription *description)
+{
+  PangoHbFontMap *self = PANGO_HB_FONT_MAP (map);
+  PangoFontsetCached *fontset;
+  PangoLanguage *language;
+  PangoFont *font = NULL;
+
+  if (self->families->len == 0)
+    return NULL;
+
+  if (context)
+    language = pango_context_get_language (context);
+  else
+    language = NULL;
+
+  fontset = (PangoFontsetCached *)pango_font_map_load_fontset (map, context, description, language);
+  if (pango_fontset_cached_size (fontset) > 0)
+    font = pango_fontset_cached_get_first_font (fontset);
+  g_object_unref (fontset);
+
+  return font;
+}
+
+/* Add one font for each family we find */
+static PangoFontset *
+pango_hb_font_map_load_fontset (PangoFontMap               *map,
+                                PangoContext               *context,
+                                const PangoFontDescription *description,
+                                PangoLanguage              *language)
+{
+  PangoHbFontMap *self = PANGO_HB_FONT_MAP (map);
+  PangoFontsetCached lookup;
+  PangoFontsetCached *fontset;
+  const PangoMatrix *matrix;
+  const char *family_name;
+  char **families;
+  PangoFontDescription *copy;
+  PangoFontFamily *family;
+  PangoHbFace *face;
+  gboolean has_generic = FALSE;
+  gint64 before G_GNUC_UNUSED;
+
+  before = PANGO_TRACE_CURRENT_TIME;
+
+  if (!language)
+    language = pango_context_get_language (context);
+
+  family_name = pango_font_description_get_family (description);
+
+  lookup.language = language;
+  lookup.description = (PangoFontDescription *)description;
+  fontset = g_hash_table_lookup (self->fontsets, &lookup);
+
+  if (fontset)
+    goto done;
+
+  matrix = pango_context_get_matrix (context);
+
+  fontset = pango_fontset_cached_new (description, language, self->dpi, matrix);
+
+  if (self->families->len == 0)
+    {
+      g_warning ("Font map contains no fonts!!!!");
+      goto done_no_cache;
+    }
+
+  families = g_strsplit (family_name ? family_name : "", ",", -1);
+
+  /* Unset gravity and variant since PangoHbFace does not have these fields */
+  copy = pango_font_description_copy_static (description);
+  pango_font_description_unset_fields (copy, PANGO_FONT_MASK_VARIATIONS |
+                                             PANGO_FONT_MASK_GRAVITY |
+                                             PANGO_FONT_MASK_VARIANT);
+
+  for (int i = 0; families[i]; i++)
+    {
+      family = find_family (self, families[i]);
+      if (!family)
+        continue;
+
+      if (PANGO_IS_GENERIC_FAMILY (family))
+        {
+          pango_fontset_cached_add_family (fontset, PANGO_GENERIC_FAMILY (family));
+          has_generic = TRUE;
+        }
+      else
+        {
+          face = pango_hb_family_find_face (PANGO_HB_FAMILY (family), copy, language, 0);
+          if (face)
+            pango_fontset_cached_add_face (fontset, face);
+        }
+    }
+
+  g_strfreev (families);
+
+  /* Returning an empty fontset leads to bad outcomes.
+   *
+   * We always include a generic family in order
+   * to produce fontsets with good coverage.
+   */
+  if (!has_generic)
+    {
+      family = find_family (self, "sans-serif");
+      if (PANGO_IS_GENERIC_FAMILY (family))
+        pango_fontset_cached_add_family (fontset, PANGO_GENERIC_FAMILY (family));
+    }
+
+  pango_font_description_free (copy);
+
+  g_hash_table_add (self->fontsets, fontset);
+
+done:
+  pango_fontset_cache (fontset, self);
+
+  if (pango_fontset_cached_size (fontset) == 0)
+    {
+      char *s = pango_font_description_to_string (description);
+      g_warning ("All font fallbacks failed for \"%s\", in %s !!!!", s, pango_language_to_string (language));
+      g_free (s);
+    }
+
+done_no_cache:
+  pango_trace_mark (before, "pango_hb_fontmap_load_fontset", "%s", family_name);
+
+  return g_object_ref (PANGO_FONTSET (fontset));
+}
+
+static void
+pango_hb_font_map_list_families (PangoFontMap      *map,
+                                     PangoFontFamily ***families,
+                                     int               *n_families)
+{
+  PangoHbFontMap *self = PANGO_HB_FONT_MAP (map);
+
+  if (n_families)
+    *n_families = self->families->len;
+
+  if (families)
+    *families = g_memdup2 (self->families->pdata, self->families->len * sizeof (PangoFontFamily *));
+}
+
+static PangoFontFamily *
+pango_hb_font_map_get_family (PangoFontMap *map,
+                              const char   *name)
+{
+  PangoHbFontMap *self = PANGO_HB_FONT_MAP (map);
+
+  return PANGO_FONT_FAMILY (find_family (self, name));
+}
+
+static void
+pango_hb_font_map_populate (PangoHbFontMap *self)
+{
+}
+
+static guint
+pango_hb_font_map_get_serial (PangoFontMap *map)
+{
+  PangoHbFontMap *self = PANGO_HB_FONT_MAP (map);
+
+  return self->serial;
+}
+
+static void
+pango_hb_font_map_changed (PangoFontMap *map)
+{
+  PangoHbFontMap *self = PANGO_HB_FONT_MAP (map);
+
+  self->serial++;
+  if (self->serial == 0)
+    self->serial++;
+}
+
+static void
+pango_hb_font_map_class_init (PangoHbFontMapClass *class)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+  PangoFontMapClass *fontmap_class = PANGO_FONT_MAP_CLASS (class);
+
+  object_class->finalize = pango_hb_font_map_finalize;
+
+  fontmap_class->load_font = pango_hb_font_map_load_font;
+  fontmap_class->load_fontset = pango_hb_font_map_load_fontset;
+  fontmap_class->list_families = pango_hb_font_map_list_families;
+  fontmap_class->get_family = pango_hb_font_map_get_family;
+  fontmap_class->get_serial = pango_hb_font_map_get_serial;
+  fontmap_class->changed = pango_hb_font_map_changed;
+
+  class->populate = pango_hb_font_map_populate;
+}
+
+/* }}} */
+/* {{{ Private API */
+
+/*< private >
+ * pango_hb_font_map_repopulate:
+ * @self: a `PangoHbFontMap`
+ * @add_synthetic: if `TRUE`, missing bold and italic faces will be synthesized
+ *
+ * Clear all cached information and repopulate the fontmap with
+ * families and faces.
+ *
+ * Subclasses should call this when their configuration changes
+ * in a way that requires recreating families and faces.
+ */
+void
+pango_hb_font_map_repopulate (PangoHbFontMap *self,
+                              gboolean        add_synthetic)
+{
+  int removed, added;
+
+  clear_caches (self);
+
+  removed = self->families->len;
+
+  g_hash_table_remove_all (self->families_hash);
+  g_ptr_array_set_size (self->families, 0);
+
+  self->in_populate = TRUE;
+
+  PANGO_HB_FONT_MAP_GET_CLASS (self)->populate (self);
+
+  if (add_synthetic)
+    synthesize_bold_and_italic_faces (self);
+
+  for (int i = 0; i < self->added_faces->len; i++)
+    {
+      PangoHbFace *face = PANGO_HB_FACE (g_ptr_array_index (self->added_faces, i));
+      pango_hb_font_map_add_face (self, face);
+    }
+
+  for (int i = 0; i < self->added_families->len; i++)
+    {
+      PangoFontFamily *family = PANGO_FONT_FAMILY (g_ptr_array_index (self->added_families, i));
+      pango_hb_font_map_add_family (self, family);
+    }
+
+  self->in_populate = FALSE;
+
+  added = self->families->len;
+
+  g_list_model_items_changed (G_LIST_MODEL (self), 0, removed, added);
+  pango_font_map_changed (PANGO_FONT_MAP (self));
+}
+
+/* }}} */
+/* {{{ Public API */
+
+/**
+ * pango_hb_font_map_new:
+ *
+ * Creates a new `PangoHbFontmMap`.
+ *
+ * Returns: A newly created `PangoHbFontMap
+ *
+ * Since: 1.52
+ */
+PangoHbFontMap *
+pango_hb_font_map_new (void)
+{
+  return g_object_new (PANGO_TYPE_HB_FONT_MAP, NULL);
+}
+
+/**
+ * pango_hb_font_map_add_face:
+ * @self: a `PangoHbFontMap`
+ * @face: (transfer full): a `PangoHbFace`
+ *
+ * Adds @face to the `PangoHbFontMap`.
+ *
+ * This is most useful for creating transformed faces or aliases.
+ * See [ctor@Pango.HbFace.new_synthetic] and [ctor@Pango.HbFace.new_instance].
+ *
+ * Since: 1.52
+ */
+void
+pango_hb_font_map_add_face (PangoHbFontMap *self,
+                            PangoHbFace    *face)
+{
+  PangoFontMap *map = PANGO_FONT_MAP (self);
+  const char *family_name;
+  PangoHbFamily *family;
+
+  if (pango_font_description_get_set_fields (face->description) &
+      (PANGO_FONT_MASK_VARIANT | PANGO_FONT_MASK_GRAVITY))
+    g_warning ("Font description for PangoHbFace includes things that it shouldn't");
+
+  if (!self->in_populate)
+    g_ptr_array_add (self->added_faces, g_object_ref (face));
+
+  family_name = pango_font_description_get_family (face->description);
+  family = PANGO_HB_FAMILY (pango_font_map_get_family (map, family_name));
+  if (!family)
+    {
+      family = pango_hb_family_new (family_name);
+      pango_hb_font_map_add_family (self, PANGO_FONT_FAMILY (family));
+    }
+
+  pango_hb_family_add_face (family, face);
+
+  pango_font_map_changed (PANGO_FONT_MAP (self));
+
+  clear_caches (self);
+}
+
+/**
+ * pango_hb_font_map_remove_face:
+ * @self: a `PangoHbFontMap`
+ * @face: a `PangoHbFace` that belongs to @map
+ *
+ * Removes @face from the `PangoHbFontMap`.
+ *
+ * @face must have been added with [method@Pango.HbFontMap.add_face].
+ *
+ * Since: 1.52
+ */
+void
+pango_hb_font_map_remove_face (PangoHbFontMap *self,
+                               PangoHbFace    *face)
+{
+  PangoHbFamily *family;
+  unsigned int position;
+
+  if (!g_ptr_array_find (self->added_faces, face, &position))
+    return;
+
+  family = PANGO_HB_FAMILY (pango_font_face_get_family (PANGO_FONT_FACE (face)));
+
+  pango_hb_family_remove_face (family, face);
+
+  if (family->faces->len == 0)
+    pango_hb_font_map_remove_family (self, PANGO_FONT_FAMILY (family));
+
+  pango_font_map_changed (PANGO_FONT_MAP (self));
+
+  clear_caches (self);
+
+  g_ptr_array_remove_index (self->added_faces, position);
+}
+
+/**
+ * pango_hb_font_map_add_file:
+ * @self: a `PangoHbFontMap`
+ * @file: font filename
+ *
+ * Creates a new `PangoHbFace` and adds it.
+ *
+ * If you need to specify an instance id or other
+ * parameters, use [ctor@Pango.HbFace.new_from_file].
+ *
+ * Since: 1.52
+ */
+void
+pango_hb_font_map_add_file (PangoHbFontMap *self,
+                            const char     *file)
+{
+  PangoHbFace *face;
+
+  face = pango_hb_face_new_from_file (file, 0, -1, NULL, NULL);
+  pango_hb_font_map_add_face (self, face);
+}
+
+/**
+ * pango_hb_font_map_add_family:
+ * @self: a `PangoHbFontMap`
+ * @family: (transfer full): a `PangoFontFamily`
+ *
+ * Adds @family to @self.
+ *
+ * The fontmap must not contain a family with the
+ * same name as @family yet.
+ *
+ * This is mostly useful for adding generic families
+ * using [ctor@Pango.GenericFamily.new].
+ */
+void
+pango_hb_font_map_add_family (PangoHbFontMap  *self,
+                              PangoFontFamily *family)
+{
+  const char *name;
+  int position;
+
+  g_return_if_fail (PANGO_IS_HB_FAMILY (family) || PANGO_IS_GENERIC_FAMILY (family));
+
+  if (!self->in_populate)
+    g_ptr_array_add (self->added_families, g_object_ref (family));
+
+  name = pango_font_family_get_name (PANGO_FONT_FAMILY (family));
+
+  position = 0;
+  while (position < self->families->len)
+    {
+      PangoFontFamily *f = g_ptr_array_index (self->families, position);
+      if (g_ascii_strcasecmp (name, pango_font_family_get_name (f)) < 0)
+        break;
+      position++;
+    }
+
+  if (PANGO_IS_HB_FAMILY (family))
+    pango_hb_family_set_font_map (PANGO_HB_FAMILY (family), PANGO_FONT_MAP (self));
+  else
+    pango_generic_family_set_font_map (PANGO_GENERIC_FAMILY (family), PANGO_FONT_MAP (self));
+
+  g_ptr_array_insert (self->families, position, family);
+  g_hash_table_add (self->families_hash, family);
+
+  if (!self->in_populate)
+    g_list_model_items_changed (G_LIST_MODEL (self), position, 0, 1);
+
+  pango_font_map_changed (PANGO_FONT_MAP (self));
+}
+
+/**
+ * pango_hb_font_map_remove_family:
+ * @self: a `PangoHbFontMap`
+ * @family: a `PangoFontFamily` that belongs to @self
+ *
+ * Removes a `PangoHbFamily` from a `PangoHbFontMap`
+ */
+void
+pango_hb_font_map_remove_family (PangoHbFontMap  *self,
+                                 PangoFontFamily *family)
+{
+  unsigned int position;
+
+  g_return_if_fail (PANGO_IS_HB_FAMILY (family) || PANGO_IS_GENERIC_FAMILY (family));
+
+  if (!g_ptr_array_find (self->added_families, family, &position))
+    return;
+
+  g_hash_table_remove (self->families_hash, family);
+  g_ptr_array_remove_index (self->families, position);
+
+  if (PANGO_IS_HB_FAMILY (family))
+    pango_hb_family_set_font_map (PANGO_HB_FAMILY (family), NULL);
+  else
+    pango_generic_family_set_font_map (PANGO_GENERIC_FAMILY (family), NULL);
+
+  if (!self->in_populate)
+    g_list_model_items_changed (G_LIST_MODEL (self), position, 1, 0);
+
+  pango_font_map_changed (PANGO_FONT_MAP (self));
+
+  g_ptr_array_remove_index (self->added_families, position);
+}
+
+/**
+ * pango_hb_font_map_set_resolution:
+ * @self: a `PangoHbFontMap`
+ * @dpi: the new resolution, in "dots per inch"
+ *
+ * Sets the resolution for the fontmap.
+ *
+ * This is a scale factor between points specified in a
+ * `PangoFontDescription` and Cairo units. The default value
+ * is 96, meaning that a 10 point font will be 13 units high.
+ * (10 * 96. / 72. = 13.3).
+ *
+ * Since: 1.52
+ */
+void
+pango_hb_font_map_set_resolution (PangoHbFontMap *self,
+                                  double          dpi)
+{
+  self->dpi = dpi;
+  clear_caches (self);
+  pango_font_map_changed (PANGO_FONT_MAP (self));
+}
+
+/* }}} */
+
+/* vim:set foldmethod=marker expandtab: */
diff --git a/pango/pango-hbfontmap.h b/pango/pango-hbfontmap.h
new file mode 100644
index 00000000..3ced207d
--- /dev/null
+++ b/pango/pango-hbfontmap.h
@@ -0,0 +1,60 @@
+/* Pango
+ *
+ * Copyright (C) 2021 Matthias Clasen
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#pragma once
+
+#include <pango/pango-types.h>
+#include <pango/pango-fontmap.h>
+#include <pango/pango-hbface.h>
+
+G_BEGIN_DECLS
+
+#define PANGO_TYPE_HB_FONT_MAP   (pango_hb_font_map_get_type ())
+
+PANGO_AVAILABLE_IN_1_52
+PANGO_DECLARE_INTERNAL_TYPE (PangoHbFontMap, pango_hb_font_map, PANGO, HB_FONT_MAP, PangoFontMap)
+
+PANGO_AVAILABLE_IN_1_52
+PangoHbFontMap *        pango_hb_font_map_new                   (void);
+
+PANGO_AVAILABLE_IN_1_52
+void                    pango_hb_font_map_add_file              (PangoHbFontMap *self,
+                                                                 const char     *file);
+
+PANGO_AVAILABLE_IN_1_52
+void                    pango_hb_font_map_add_face              (PangoHbFontMap *self,
+                                                                 PangoHbFace    *face);
+
+PANGO_AVAILABLE_IN_1_52
+void                    pango_hb_font_map_remove_face           (PangoHbFontMap *self,
+                                                                 PangoHbFace    *face);
+
+PANGO_AVAILABLE_IN_1_52
+void                    pango_hb_font_map_add_family            (PangoHbFontMap  *self,
+                                                                 PangoFontFamily *family);
+PANGO_AVAILABLE_IN_1_52
+void                    pango_hb_font_map_remove_family         (PangoHbFontMap  *self,
+                                                                 PangoFontFamily *family);
+
+PANGO_AVAILABLE_IN_1_52
+void                    pango_hb_font_map_set_resolution        (PangoHbFontMap *self,
+                                                                 double          dpi);
+
+G_END_DECLS
diff --git a/pango/pango.h b/pango/pango.h
index a1af0802..9d95b5e5 100644
--- a/pango/pango.h
+++ b/pango/pango.h
@@ -42,6 +42,7 @@
 #include <pango/pango-gravity.h>
 #include <pango/pango-hbface.h>
 #include <pango/pango-hbfont.h>
+#include <pango/pango-hbfontmap.h>
 #include <pango/pango-item.h>
 #include <pango/pango-language.h>
 #include <pango/pango-layout.h>