Add PangoHbFace

PangoHbFace is a simple wrapper around hb_face_t.

This is an attempt to make a font backend that does
not depend on platform specifics and can be used in
tests.

5 files changed, 1151 insertions, 0 deletions

diff --git a/pango/meson.build b/pango/meson.build
index c8713582..c12aa1bf 100644
--- a/pango/meson.build
+++ b/pango/meson.build
@@ -34,6 +34,7 @@ pango_sources = [
   'serializer.c',
   'json/gtkjsonparser.c',
   'json/gtkjsonprinter.c',
+  'pango-hbface.c',
 ]
 
 pango_headers = [
@@ -64,6 +65,7 @@ pango_headers = [
   'pango-tabs.h',
   'pango-types.h',
   'pango-utils.h',
+  'pango-hbface.h',
 ]
 
 pango_installed_headers = pango_headers + [ 'pango-version-macros.h' ]
diff --git a/pango/pango-hbface-private.h b/pango/pango-hbface-private.h
new file mode 100644
index 00000000..045a13ef
--- /dev/null
+++ b/pango/pango-hbface-private.h
@@ -0,0 +1,66 @@
+/* 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-hbface.h"
+#include "pango-fontmap.h"
+#include "pango-language-set-private.h"
+#include <hb.h>
+
+struct _PangoHbFace
+{
+  PangoFontFace parent_instance;
+
+  unsigned int index;
+  int instance_id;
+  char *file;
+  hb_face_t *face;
+  char *psname;
+  char *faceid;
+  hb_variation_t *variations;
+  unsigned int n_variations;
+  char *name;
+  PangoFontFamily *family;
+  PangoFontDescription *description;
+  PangoMatrix *matrix;
+  double x_scale, y_scale;
+  PangoLanguageSet *languages;
+  gboolean embolden;
+  gboolean synthetic;
+};
+
+void                    pango_hb_face_set_family        (PangoHbFace          *self,
+                                                         PangoFontFamily      *family);
+
+PangoLanguageSet *      pango_hb_face_get_language_set  (PangoHbFace          *self);
+
+PANGO_AVAILABLE_IN_1_52
+void                    pango_hb_face_set_language_set  (PangoHbFace          *self,
+                                                         PangoLanguageSet     *languages);
+
+PANGO_AVAILABLE_IN_1_52
+void                    pango_hb_face_set_matrix        (PangoHbFace          *self,
+                                                         const PangoMatrix    *matrix);
+
+gboolean                pango_hb_face_has_char          (PangoHbFace          *self,
+                                                         gunichar              wc);
+
+const char *            pango_hb_face_get_faceid        (PangoHbFace          *self);
diff --git a/pango/pango-hbface.c b/pango/pango-hbface.c
new file mode 100644
index 00000000..7c93f9aa
--- /dev/null
+++ b/pango/pango-hbface.c
@@ -0,0 +1,998 @@
+/* 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 "pango-font-private.h"
+#include "pango-hbface-private.h"
+
+#include "pango-language-set-simple-private.h"
+
+#include <string.h>
+#include <hb-ot.h>
+
+/**
+ * PangoHbFace:
+ *
+ * `PangoHbFace` is a `PangoFontFace` implementation that wraps
+ * a `hb_face_t` object and implements all of the `PangoFontFace`
+ * functionality using HarfBuzz.
+ *
+ * In addition to making a `hb_face_t` available for rendering
+ * glyphs with Pango, `PangoHbFace` allows some tweaks to the
+ * rendering, such as artificial slant (using a transformation
+ * matrix) or artificial emboldening.
+ */
+
+ /* {{{ Utilities */
+
+static char *
+get_name_from_hb_face (hb_face_t       *face,
+                       hb_ot_name_id_t  name_id,
+                       hb_ot_name_id_t  fallback_id)
+{
+  char buf[256];
+  unsigned int len;
+
+  len = sizeof (buf);
+  if (hb_ot_name_get_utf8 (face, name_id, HB_LANGUAGE_INVALID, &len, buf) > 0)
+    return g_strdup (buf);
+
+  if (fallback_id != HB_OT_NAME_ID_INVALID)
+    {
+      len = sizeof (buf);
+      if (hb_ot_name_get_utf8 (face, fallback_id, HB_LANGUAGE_INVALID, &len, buf) > 0)
+        return g_strdup (buf);
+    }
+
+  return g_strdup ("Unnamed");
+}
+
+static void
+ensure_hb_face (PangoHbFace *self)
+{
+  hb_blob_t *blob;
+
+  if (self->face)
+    return;
+
+  blob = hb_blob_create_from_file (self->file);
+
+  if (blob == hb_blob_get_empty ())
+    g_warning ("Failed to load %s", self->file);
+
+  if (self->index >= hb_face_count (blob))
+    g_warning ("Face index %d out of range for %s", self->index, self->file);
+
+  self->face = hb_face_create (blob, self->index);
+
+  if (self->instance_id >= (int)hb_ot_var_get_named_instance_count (self->face))
+    g_warning ("Instance ID %d out of range for %s", self->instance_id, self->file);
+
+  hb_blob_destroy (blob);
+  hb_face_make_immutable (self->face);
+}
+
+static char *
+variations_to_string (const hb_variation_t *variations,
+                      unsigned int          n_variations,
+                      const char           *equals,
+                      const char           *separator)
+{
+  GString *s;
+  char buf[128] = { 0, };
+
+  s = g_string_new ("");
+
+  for (unsigned int i = 0; i < n_variations; i++)
+    {
+      if (s->len > 0)
+        g_string_append (s, separator);
+
+      hb_tag_to_string (variations[i].tag, buf);
+      g_string_append (s, buf);
+      g_string_append (s, equals);
+      g_ascii_formatd (buf, sizeof (buf), "%g", variations[i].value);
+      g_string_append (s, buf);
+    }
+
+  return g_string_free (s, FALSE);
+}
+
+static void
+set_name_and_description (PangoHbFace                *self,
+                          const char                 *name,
+                          const PangoFontDescription *description)
+{
+  if (name)
+    {
+      self->name = g_strdup (name);
+    }
+  else
+    {
+      hb_ot_name_id_t name_id;
+
+      ensure_hb_face (self);
+
+      if (self->instance_id >= 0)
+        name_id = hb_ot_var_named_instance_get_subfamily_name_id (self->face, self->instance_id);
+      else
+        name_id = HB_OT_NAME_ID_TYPOGRAPHIC_SUBFAMILY;
+
+      self->name = get_name_from_hb_face (self->face, name_id, HB_OT_NAME_ID_FONT_SUBFAMILY);
+    }
+
+  if (description)
+    {
+      self->description = pango_font_description_copy (description);
+    }
+  else
+    {
+      char *family;
+      char *fullname;
+
+      ensure_hb_face (self);
+
+      family = get_name_from_hb_face (self->face,
+                                      HB_OT_NAME_ID_TYPOGRAPHIC_FAMILY,
+                                      HB_OT_NAME_ID_FONT_FAMILY);
+      fullname = g_strconcat (family, " ", self->name, NULL);
+
+      self->description = pango_font_description_from_string (fullname);
+      pango_font_description_unset_fields (self->description,
+                                           PANGO_FONT_MASK_VARIANT |
+                                           PANGO_FONT_MASK_VARIATIONS |
+                                           PANGO_FONT_MASK_GRAVITY);
+
+      g_free (fullname);
+      g_free (family);
+    }
+
+  if (self->n_variations > 0)
+    {
+      char *str = variations_to_string (self->variations, self->n_variations, "=", ",");
+      pango_font_description_set_variations (self->description, str);
+      g_free (str);
+    }
+}
+
+typedef struct {
+  guint16 major;
+  guint16 minor;
+  gint32 italicAngle;
+  gint16 underlinePosition;
+  gint16 underlineThickness;
+  guint8 isFixedPitch[4];
+} PostTable;
+
+static gboolean
+hb_face_is_monospace (hb_face_t *face)
+{
+  hb_blob_t *post_blob;
+  guint8 *raw_post;
+  unsigned int post_len;
+  gboolean res = FALSE;
+
+  post_blob = hb_face_reference_table (face, HB_TAG ('p', 'o', 's', 't'));
+  raw_post = (guint8 *) hb_blob_get_data (post_blob, &post_len);
+
+  if (post_len >= sizeof (PostTable))
+    {
+      PostTable *post = (PostTable *)raw_post;
+
+      res = post->isFixedPitch[0] != 0 ||
+            post->isFixedPitch[1] != 0 ||
+            post->isFixedPitch[2] != 0 ||
+            post->isFixedPitch[3] != 0;
+    }
+
+  hb_blob_destroy (post_blob);
+
+  return res;
+}
+
+static void
+ensure_psname (PangoHbFace *self)
+{
+  char *p;
+
+  if (self->psname)
+    return;
+
+  ensure_hb_face (self);
+
+  self->psname = get_name_from_hb_face (self->face, HB_OT_NAME_ID_POSTSCRIPT_NAME, HB_OT_NAME_ID_INVALID);
+
+  /* PostScript name should not contain problematic chars, but just in case,
+   * make sure we don't have any ' ', '=' or ',' that would give us parsing
+   * problems.
+   */
+  p = self->psname;
+  while ((p = strpbrk (p, " =,")) != NULL)
+    *p = '?';
+}
+
+static const char *
+style_from_font_description (const PangoFontDescription *desc)
+{
+  PangoStyle style = pango_font_description_get_style (desc);
+  PangoWeight weight = pango_font_description_get_weight (desc);
+
+  switch (style)
+    {
+    case PANGO_STYLE_ITALIC:
+      if (weight == PANGO_WEIGHT_BOLD)
+        return "Bold Italic";
+      else
+        return "Italic";
+      break;
+    case PANGO_STYLE_OBLIQUE:
+      if (weight == PANGO_WEIGHT_BOLD)
+        return "Bold Oblique";
+      else
+        return "Oblique";
+      break;
+    case PANGO_STYLE_NORMAL:
+      if (weight == PANGO_WEIGHT_BOLD)
+        return "Bold";
+      else
+        return "Regular";
+      break;
+    default: ;
+    }
+
+  return NULL;
+}
+
+/* }}} */
+/* {{{ PangoFontFace implementation */
+
+struct _PangoHbFaceClass
+{
+  PangoFontFaceClass parent_class;
+};
+
+G_DEFINE_TYPE (PangoHbFace, pango_hb_face, PANGO_TYPE_FONT_FACE)
+
+static void
+pango_hb_face_init (PangoHbFace *self)
+{
+  self->matrix = NULL;
+  self->x_scale = self->y_scale = 1.;
+}
+
+static void
+pango_hb_face_finalize (GObject *object)
+{
+  PangoHbFace *self = PANGO_HB_FACE (object);
+
+  hb_face_destroy (self->face);
+  pango_font_description_free (self->description);
+  g_free (self->name);
+  g_free (self->file);
+  g_free (self->faceid);
+  if (self->languages)
+    g_object_unref (self->languages);
+  g_free (self->variations);
+  if (self->matrix)
+    g_free (self->matrix);
+
+  G_OBJECT_CLASS (pango_hb_face_parent_class)->finalize (object);
+}
+
+static const char *
+pango_hb_face_get_face_name (PangoFontFace *face)
+{
+  PangoHbFace *self = PANGO_HB_FACE (face);
+
+  return self->name;
+}
+
+static PangoFontDescription *
+pango_hb_face_describe (PangoFontFace *face)
+{
+  PangoHbFace *self = PANGO_HB_FACE (face);
+
+  if ((pango_font_description_get_set_fields (self->description) & PANGO_FONT_MASK_FACEID) == 0)
+    pango_font_description_set_faceid (self->description, pango_hb_face_get_faceid (self));
+
+  return pango_font_description_copy (self->description);
+}
+
+static PangoFontFamily *
+pango_hb_face_get_family (PangoFontFace *face)
+{
+  PangoHbFace *self = PANGO_HB_FACE (face);
+
+  return self->family;
+}
+
+static gboolean
+pango_hb_face_is_synthesized (PangoFontFace *face)
+{
+  PangoHbFace *self = PANGO_HB_FACE (face);
+
+  return self->synthetic;
+}
+
+static gboolean
+pango_hb_face_is_monospace (PangoFontFace *face)
+{
+  PangoHbFace *self = PANGO_HB_FACE (face);
+
+  ensure_hb_face (self);
+
+  return hb_face_is_monospace (self->face);
+}
+
+static gboolean
+pango_hb_face_is_variable (PangoFontFace *face)
+{
+  PangoHbFace *self = PANGO_HB_FACE (face);
+
+  /* We don't consider named instances as variable, i.e.
+   * a font chooser UI should not expose axes for them.
+   *
+   * In theory, there could be multi-axis fonts where the
+   * variations only pin some of the axes, but we are not
+   * going to worry about possibility here.
+   */
+  if (self->instance_id >= -1 || self->n_variations)
+    return FALSE;
+
+  ensure_hb_face (self);
+
+  return hb_ot_var_get_axis_count (self->face) > 0;
+}
+
+static gboolean
+pango_hb_face_supports_language (PangoFontFace *face,
+                                 PangoLanguage *language)
+{
+  PangoHbFace *self = PANGO_HB_FACE (face);
+  PangoLanguageSet *set = pango_hb_face_get_language_set (self);
+
+  if (set)
+    return pango_language_set_matches_language (set, language);
+
+  return TRUE;
+}
+
+static PangoLanguage **
+pango_hb_face_get_languages (PangoFontFace *face)
+{
+  PangoHbFace *self = PANGO_HB_FACE (face);
+  PangoLanguageSet *set = pango_hb_face_get_language_set (self);
+
+  if (set)
+    return pango_language_set_get_languages (set);
+
+  return NULL;
+}
+
+static void
+pango_hb_face_class_init (PangoHbFaceClass *class)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+  PangoFontFaceClass *face_class = PANGO_FONT_FACE_CLASS (class);
+  PangoFontFaceClassPrivate *pclass;
+
+  object_class->finalize = pango_hb_face_finalize;
+
+  face_class->get_face_name = pango_hb_face_get_face_name;
+  face_class->describe = pango_hb_face_describe;
+  face_class->list_sizes = NULL;
+  face_class->is_synthesized = pango_hb_face_is_synthesized;
+  face_class->get_family = pango_hb_face_get_family;
+  face_class->is_monospace = pango_hb_face_is_monospace;
+  face_class->is_variable = pango_hb_face_is_variable;
+
+  pclass = g_type_class_get_private ((GTypeClass *) class, PANGO_TYPE_FONT_FACE);
+
+  pclass->supports_language = pango_hb_face_supports_language;
+  pclass->get_languages = pango_hb_face_get_languages;
+}
+
+/* }}} */
+/* {{{ Private API */
+
+/*< private >
+ * pango_hb_face_set_family:
+ * @self: a `PangoHbFace`
+ * @family: a `PangoFontFamily`
+ *
+ * Sets the font family of a `PangoHbFace`.
+ *
+ * This should only be called by fontmap implementations.
+ */
+void
+pango_hb_face_set_family (PangoHbFace     *self,
+                          PangoFontFamily *family)
+{
+  self->family = family;
+}
+
+/*< private >
+ * pango_hb_face_get_language_set:
+ * @face: a `PangoHbFace`
+ *
+ * Returns the languages supported by @face.
+ *
+ * Returns: (transfer none): a `PangoLanguageSet`
+ */
+PangoLanguageSet *
+pango_hb_face_get_language_set (PangoHbFace *face)
+{
+  return face->languages;
+}
+
+/*< private >
+ * pango_hb_face_set_languages:
+ * @self: a `PangoHbFace`
+ * @languages: a `PangoLanguageSet`
+ *
+ * Sets the languages that are supported by @face.
+ *
+ * This should only be called by fontmap implementations.
+ */
+void
+pango_hb_face_set_language_set (PangoHbFace      *self,
+                                PangoLanguageSet *languages)
+{
+  g_set_object (&self->languages, languages);
+}
+
+/*< private  >
+ * pango_hb_face_set_matrix:
+ * @self: a `PangoHbFace`
+ * @matrix: the `PangoMatrix`
+ *
+ * Sets the font matrix for @self.
+ *
+ * This should only be called by fontmap implementations.
+ */
+void
+pango_hb_face_set_matrix (PangoHbFace       *self,
+                          const PangoMatrix *matrix)
+{
+  if (!self->matrix)
+    self->matrix = g_new (PangoMatrix, 1);
+
+  *self->matrix = *matrix;
+
+  pango_matrix_get_font_scale_factors (self->matrix, &self->x_scale, &self->y_scale);
+  pango_matrix_scale (self->matrix, 1./self->x_scale, 1./self->y_scale);
+}
+
+/*< private >
+ * pango_hb_face_has_char:
+ * @self: a `PangoHbFace`
+ * @wc: a Unicode character
+ *
+ * Returns whether the face provides a glyph for this character.
+ *
+ * Returns: `TRUE` if @font can render @wc
+ */
+gboolean
+pango_hb_face_has_char (PangoHbFace *self,
+                        gunichar     wc)
+{
+  hb_font_t *hb_font;
+  hb_codepoint_t glyph;
+  gboolean ret;
+
+  ensure_hb_face (self);
+
+  hb_font = hb_font_create (self->face);
+  ret = hb_font_get_nominal_glyph (hb_font, wc, &glyph);
+  hb_font_destroy (hb_font);
+
+  return ret;
+}
+
+/*< private >
+ * pango_hb_face_get_faceid:
+ * @self: a `PangoHbFace`
+ *
+ * Returns the faceid of the face.
+ *
+ * The faceid is meant to uniquely identify the face among the
+ * faces of its family. It includes an identifier for the font
+ * file that is used (currently, we use the PostScript name for
+ * this), the face index, the instance ID, as well as synthetic
+ * tweaks such as emboldening and transforms and variations.
+ *
+ * [method@Pango.FontFace.describe] adds the faceid to the font
+ * description that it produces.
+ *
+ * See pango_hb_family_find_face() for the code that takes the
+ * faceid into account when searching for a face. It is careful
+ * to fall back to approximate matching if an exact match for
+ * the faceid isn't found. That should make it safe to preserve
+ * faceids when saving font descriptions in configuration or
+ * other data.
+ *
+ * There are no guarantees about the format of the string that
+ * this function produces, except for that it does not contain
+ * ' ', ',' or '=', so it can be safely embedded in the '@' part
+ * of a serialized font description.
+ *
+ * Returns: (transfer none): the faceid
+ */
+const char *
+pango_hb_face_get_faceid (PangoHbFace *self)
+{
+  if (!self->faceid)
+    {
+      double slant;
+      char buf0[32], buf1[32], buf2[32];
+      char *str = NULL;
+
+      ensure_psname (self);
+
+      if (self->matrix)
+        slant = pango_matrix_get_slant_ratio (self->matrix);
+      else
+        slant = 0.;
+
+      if (self->n_variations > 0)
+        str = variations_to_string (self->variations, self->n_variations, "_", ":");
+
+      self->faceid = g_strdup_printf ("hb:%s:%u:%d:%d:%s:%s:%s%s%s",
+                                      self->psname,
+                                      self->index,
+                                      self->instance_id,
+                                      self->embolden,
+                                      g_ascii_formatd (buf0, sizeof (buf0), "%g", self->x_scale),
+                                      g_ascii_formatd (buf1, sizeof (buf1), "%g", self->y_scale),
+                                      g_ascii_formatd (buf2, sizeof (buf2), "%g", slant),
+                                      self->n_variations > 0 ? ":" : "",
+                                      self->n_variations > 0 ? str : "");
+      g_free (str);
+    }
+
+  return self->faceid;
+}
+
+/* }}} */
+ /* {{{ Public API */
+
+/**
+ * pango_hb_face_new_from_hb_face:
+ * @face: an immutable `hb_face_t`
+ * @instance_id: named instance id, or -1 for the default instance
+ *   or -2 for no instance
+ * @name: (nullable): name for the face
+ * @description: (nullable): `PangoFontDescription` for the font
+ *
+ * Creates a new `PangoHbFace` by wrapping an existing `hb_face_t`.
+ *
+ * The @instance_id can be used to pick one of the available named
+ * instances in a variable font. See hb_ot_var_get_named_instance_count()
+ * to learn about the available named instances.
+ *
+ * If @instance_id is -2 and @face has variation axes, then
+ * [method@Pango.FontFace.is_variable] will return `TRUE` for
+ * the returned `PangoHbFace`.
+ *
+ * If @name is provided, it is used as the name for the face.
+ * Otherwise, Pango will use the named instance subfamily name
+ * or `HB_OT_NAME_ID_TYPOGRAPHIC_SUBFAMILY`.
+ *
+ * If @description is provided, it is used as the font description
+ * for the face. Otherwise, Pango creates a description using
+ * `HB_OT_NAME_ID_TYPOGRAPHIC_FAMILY` and the name of the face.
+ *
+ * Returns: a newly created `PangoHbFace`
+ *
+ * Since: 1.52
+ */
+PangoHbFace *
+pango_hb_face_new_from_hb_face (hb_face_t                 *face,
+                                int                        instance_id,
+                                const char                 *name,
+                                const PangoFontDescription *description)
+{
+  PangoHbFace *self;
+
+  g_return_val_if_fail (hb_face_is_immutable (face), NULL);
+  g_return_val_if_fail (instance_id >= -2, NULL);
+  g_return_val_if_fail (description == NULL ||
+                        (pango_font_description_get_set_fields (description) &
+                         (PANGO_FONT_MASK_VARIANT|
+                          PANGO_FONT_MASK_SIZE|
+                          PANGO_FONT_MASK_GRAVITY)) == 0, NULL);
+
+  self = g_object_new (PANGO_TYPE_HB_FACE, NULL);
+
+  self->face = hb_face_reference (face);
+  self->index = hb_face_get_index (face) & 0xffff;
+  self->instance_id = instance_id;
+
+  if (instance_id >= (int)hb_ot_var_get_named_instance_count (face))
+    g_warning ("Instance ID %d out of range", instance_id);
+
+  set_name_and_description (self, name, description);
+
+  return self;
+}
+
+/**
+ * pango_hb_face_new_from_file:
+ * @file: font filename
+ * @index: face index
+ * @instance_id: named instance id, or -1 for the default instance
+ *   or -2 for no instance
+ * @name: (nullable): name for the face
+ * @description: (nullable): `PangoFontDescription` for the font
+ *
+ * Creates a new `PangoHbFace` from a font file.
+ *
+ * The @instance_id can be used to pick one of the available named
+ * instances in a variable font. See hb_ot_var_get_named_instance_count()
+ * to learn about the available named instances.
+ *
+ * If @instance_id is -2 and @face has variation axes, then
+ * [method@Pango.FontFace.is_variable] will return `TRUE` for
+ * the returned `PangoHbFace`.
+ *
+ * If @name is provided, it is used as the name for the face.
+ * Otherwise, Pango will use the named instance subfamily name
+ * or `HB_OT_NAME_ID_TYPOGRAPHIC_SUBFAMILY`.
+ *
+ * If @description is provided, it is used as the font description
+ * for the face. Otherwise, Pango creates a description using
+ * `HB_OT_NAME_ID_TYPOGRAPHIC_FAMILY` and the name of the face.
+ *
+ * If @desc and @name are provided, then the returned `PangoHbFace`
+ * object will be lazily initialized as needed.
+ *
+ * Returns: a newly created `PangoHbFace`
+ *
+ * Since: 1.52
+ */
+PangoHbFace *
+pango_hb_face_new_from_file (const char                 *file,
+                             unsigned int                index,
+                             int                         instance_id,
+                             const char                 *name,
+                             const PangoFontDescription *description)
+{
+  PangoHbFace *self;
+
+  g_return_val_if_fail (instance_id >= -2, NULL);
+  g_return_val_if_fail (description == NULL ||
+                        (pango_font_description_get_set_fields (description) &
+                         (PANGO_FONT_MASK_VARIANT|
+                          PANGO_FONT_MASK_SIZE|
+                          PANGO_FONT_MASK_GRAVITY)) == 0, NULL);
+
+  self = g_object_new (PANGO_TYPE_HB_FACE, NULL);
+
+  self->file = g_strdup (file);
+  self->index = index;
+  self->instance_id = instance_id;
+
+  set_name_and_description (self, name, description);
+
+  return self;
+}
+
+/**
+ * pango_hb_face_new_synthetic:
+ * @face: a `PangoHbFace`
+ * @transform: (nullable): the transform to apply
+ * @embolden: `TRUE` to render the font bolder
+ * @name: (nullable): name for the face
+ * @description: a `PangoFontDescription` to override fields from @face's description
+ *
+ * Creates a new `PangoHbFace` that is a synthetic variant of @face.
+ *
+ * Here, 'synthetic' means that the variant is implemented by rendering
+ * the glyphs differently, not by using data from the original @face.
+ * See [ctor@Pango.HbFace.new_instance] for that.
+ *
+ * @transform can be used to specify a non-trivial font matrix for creating
+ * synthetic italics or synthetic condensed variants of an existing face.
+ *
+ * If @embolden is `TRUE`, Pango will render the glyphs bolder, creating
+ * a synthetic bold variant of the face.
+ *
+ * If a @name is not specified, the name for the face will be derived
+ * from the @description.
+ *
+ * Apart from setting the style that this face will be used for,
+ * @description can provide an alternative family name. This can
+ * be used to create generic aliases such as 'sans' or 'monospace'.
+ *
+ * Note that only the following fields in @description should be set:
+ * - style or stretch, to indicate a transformed style
+ * - weight, to indicate a bolder weight
+ * - family, to provide an alternative family name
+ *
+ * [method@Pango.Face.is_synthesized] will return `TRUE` for objects
+ * created by this function.
+ *
+ * Returns: (transfer full): a newly created `PangoHbFace`
+ *
+ * Since: 1.52
+ */
+PangoHbFace *
+pango_hb_face_new_synthetic (PangoHbFace                *face,
+                             const PangoMatrix          *transform,
+                             gboolean                    embolden,
+                             const char                 *name,
+                             const PangoFontDescription *description)
+{
+  PangoHbFace *self;
+  PangoFontDescription *desc;
+
+  g_return_val_if_fail (PANGO_IS_HB_FACE (face), NULL);
+  g_return_val_if_fail (description != NULL, NULL);
+  g_return_val_if_fail ((pango_font_description_get_set_fields (description) &
+                         ~(PANGO_FONT_MASK_FAMILY|
+                           PANGO_FONT_MASK_STYLE|
+                           PANGO_FONT_MASK_STRETCH|
+                           PANGO_FONT_MASK_WEIGHT)) == 0, NULL);
+
+  self = g_object_new (PANGO_TYPE_HB_FACE, NULL);
+
+  self->file = g_strdup (face->file);
+  if (face->face)
+    self->face = hb_face_reference (face->face);
+
+  self->index = face->index;
+  self->instance_id = face->instance_id;
+  self->variations = g_memdup2 (face->variations, sizeof (hb_variation_t) * face->n_variations);
+  self->n_variations = face->n_variations;
+
+  if (transform)
+    pango_hb_face_set_matrix (self, transform);
+
+  self->embolden = embolden;
+  self->synthetic = self->embolden || (self->matrix != NULL);
+
+  desc = pango_font_description_copy (face->description);
+  pango_font_description_merge (desc, description, TRUE);
+
+  if (!name)
+    name = style_from_font_description (desc);
+
+  set_name_and_description (self, name, desc);
+
+  pango_font_description_free (desc);
+
+  return self;
+}
+
+/**
+ * pango_hb_face_new_instance:
+ * @face: a `PangoHbFace`
+ * @variations: (nullable) (array length=n_variations): font variations to apply
+ * @n_variations: length of @variations
+ * @name: (nullable): name for the face
+ * @description: a `PangoFontDescription` to override fields from @face's description
+ *
+ * Creates a new `PangoHbFace` that is a variant of @face.
+ *
+ * The @variations provide values for variation axes of @face. Axes that
+ * are not included in @variations will keep the values they have in @face.
+ * @variations that refer to axes that the face does not have are ignored.
+ *
+ * Conceptually, this is similar to a named instance of the face, except
+ * that the mapping of the name to a set of coordinates on the variation
+ * axes is provided externally, and not by the face itself.
+ *
+ * If a @name is not specified, the name for the face will be derived
+ * from the @description.
+ *
+ * Apart from setting the style that this face will be used for,
+ * @description can provide an alternative family name. This can
+ * be used to create generic aliases such as 'sans' or 'monospace'.
+ *
+ * Note that only the following fields in @description should be set:
+ * - style or stretch, to indicate a transformed style
+ * - weight, to indicate a bolder weight
+ * - family, to provide an alternative family name
+ *
+ * Returns: (transfer full): a newly created `PangoHbFace`
+ *
+ * Since: 1.52
+ */
+PangoHbFace *
+pango_hb_face_new_instance (PangoHbFace                *face,
+                            const hb_variation_t       *variations,
+                            unsigned int                n_variations,
+                            const char                 *name,
+                            const PangoFontDescription *description)
+{
+  PangoHbFace *self;
+  PangoFontDescription *desc;
+
+  g_return_val_if_fail (PANGO_IS_HB_FACE (face), NULL);
+  g_return_val_if_fail (description != NULL, NULL);
+  g_return_val_if_fail ((pango_font_description_get_set_fields (description) &
+                         ~(PANGO_FONT_MASK_FAMILY|
+                           PANGO_FONT_MASK_STYLE|
+                           PANGO_FONT_MASK_STRETCH|
+                           PANGO_FONT_MASK_WEIGHT)) == 0, NULL);
+
+  self = g_object_new (PANGO_TYPE_HB_FACE, NULL);
+
+  self->file = g_strdup (face->file);
+  if (face->face)
+    self->face = hb_face_reference (face->face);
+
+  self->index = face->index;
+  self->instance_id = face->instance_id;
+
+  if (face->matrix)
+    {
+      self->matrix = g_memdup2 (face->matrix, sizeof (PangoMatrix));
+      self->x_scale = face->x_scale;
+      self->y_scale = face->y_scale;
+    }
+
+  self->embolden = face->embolden;
+  self->synthetic = self->embolden || (self->matrix != NULL);
+
+  self->variations = g_memdup2 (variations, sizeof (hb_variation_t) * n_variations);
+  self->n_variations = n_variations;
+
+  desc = pango_font_description_copy (face->description);
+  pango_font_description_merge (desc, description, TRUE);
+
+  if (!name)
+    name = style_from_font_description (desc);
+
+  set_name_and_description (self, name, desc);
+
+  pango_font_description_free (desc);
+
+  return self;
+}
+
+/**
+ * pango_hb_face_get_hb_face:
+ * @self: a `PangoHbFace`
+ *
+ * Gets the `hb_face_t` object backing this face.
+ *
+ * Note that the objects returned by this function are cached
+ * and immutable, and may be shared between `PangoHbFace` objects.
+ *
+ * Returns: (transfer none): the `hb_face_t` object
+ *   backing the face
+ *
+ * Since: 1.52
+ */
+hb_face_t *
+pango_hb_face_get_hb_face (PangoHbFace *self)
+{
+  ensure_hb_face (self);
+
+  return self->face;
+}
+
+/**
+ * pango_hb_face_get_file:
+ * @self: a `PangoHbFace`
+ *
+ * Gets the file that backs the face.
+ *
+ * Returns: (transfer none) (nullable): the file backing the face
+ *
+ * Since: 1.52
+ */
+const char *
+pango_hb_face_get_file (PangoHbFace *self)
+{
+  return self->file;
+}
+
+/**
+ * pango_hb_face_get_face_index:
+ * @self: a `PangoHbFace`
+ *
+ * Gets the face index of the face.
+ *
+ * Returns: the face indexx
+ *
+ * Since: 1.52
+ */
+unsigned int
+pango_hb_face_get_face_index (PangoHbFace *self)
+{
+  return self->index;
+}
+
+/**
+ * pango_hb_face_get_instance_id:
+ * @self: a `PangoHbFace`
+ *
+ * Gets the instance id of the face.
+ *
+ * Returns: the instance id
+ *
+ * Since: 1.52
+ */
+int
+pango_hb_face_get_instance_id (PangoHbFace *self)
+{
+  return self->instance_id;
+}
+
+/**
+ * pango_hb_face_get_variations:
+ * @self: a `PangoHbFace`
+ * @n_variations: (nullable) (out caller-allocates): return location for
+ *   the length of the returned array
+ *
+ * Gets the variations of the face.
+ *
+ *
+ * Returns: (nullable) (transfer none): the variations
+ *
+ * Since: 1.52
+ */
+const hb_variation_t *
+pango_hb_face_get_variations (PangoHbFace  *self,
+                              unsigned int *n_variations)
+{
+  if (n_variations)
+    *n_variations = self->n_variations;
+
+  return self->variations;
+}
+
+/**
+ * pango_hb_face_get_embolden:
+ * @self: a `PangoHbFace`
+ *
+ * Gets whether face is using synthetic emboldening.
+ *
+ * Returns: `TRUE` if the face is using synthetic embolding
+ */
+gboolean
+pango_hb_face_get_embolden (PangoHbFace *self)
+{
+  return self->embolden;
+}
+
+/**
+ * pango_hb_face_get_transform:
+ * @self: a `PangoHbFace`
+ *
+ * Gets the transform that this face uses.
+ *
+ * This is the 'font matrix' which iis used for
+ * sythetic italics and width variations.
+ *
+ * Returns: (nullable) (transfer none): the transform of face
+ */
+const PangoMatrix *
+pango_hb_face_get_transform (PangoHbFace *self)
+{
+  return self->matrix;
+}
+
+/* }}} */
+
+/* vim:set foldmethod=marker expandtab: */
diff --git a/pango/pango-hbface.h b/pango/pango-hbface.h
new file mode 100644
index 00000000..80f77509
--- /dev/null
+++ b/pango/pango-hbface.h
@@ -0,0 +1,84 @@
+/* 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-font.h>
+
+G_BEGIN_DECLS
+
+#define PANGO_TYPE_HB_FACE      (pango_hb_face_get_type ())
+
+PANGO_AVAILABLE_IN_1_52
+G_DECLARE_FINAL_TYPE (PangoHbFace, pango_hb_face, PANGO, HB_FACE, PangoFontFace)
+
+PANGO_AVAILABLE_IN_1_52
+PangoHbFace *   pango_hb_face_new_from_hb_face  (hb_face_t                  *face,
+                                                 int                         instance_id,
+                                                 const char                 *name,
+                                                 const PangoFontDescription *description);
+
+PANGO_AVAILABLE_IN_1_52
+PangoHbFace *   pango_hb_face_new_from_file     (const char                 *file,
+                                                 unsigned int                index,
+                                                 int                         instance_id,
+                                                 const char                 *name,
+                                                 const PangoFontDescription *description);
+
+PANGO_AVAILABLE_IN_1_52
+PangoHbFace *   pango_hb_face_new_synthetic     (PangoHbFace                *face,
+                                                 const PangoMatrix          *transform,
+                                                 gboolean                    embolden,
+                                                 const char                 *name,
+                                                 const PangoFontDescription *description);
+
+PANGO_AVAILABLE_IN_1_52
+PangoHbFace *   pango_hb_face_new_instance      (PangoHbFace                *face,
+                                                 const hb_variation_t       *variations,
+                                                 unsigned int                n_variations,
+                                                 const char                 *name,
+                                                 const PangoFontDescription *description);
+
+PANGO_AVAILABLE_IN_1_52
+hb_face_t *     pango_hb_face_get_hb_face       (PangoHbFace            *self);
+
+PANGO_AVAILABLE_IN_1_52
+const char *    pango_hb_face_get_file          (PangoHbFace            *self);
+
+PANGO_AVAILABLE_IN_1_52
+unsigned int    pango_hb_face_get_face_index    (PangoHbFace            *self);
+
+PANGO_AVAILABLE_IN_1_52
+int             pango_hb_face_get_instance_id   (PangoHbFace            *self);
+
+PANGO_AVAILABLE_IN_1_52
+const hb_variation_t *
+                pango_hb_face_get_variations   (PangoHbFace            *self,
+                                                unsigned int           *n_variations);
+
+PANGO_AVAILABLE_IN_1_52
+gboolean        pango_hb_face_get_embolden      (PangoHbFace            *self);
+
+PANGO_AVAILABLE_IN_1_52
+const PangoMatrix *
+                pango_hb_face_get_transform     (PangoHbFace            *self);
+
+G_END_DECLS
diff --git a/pango/pango.h b/pango/pango.h
index eca66265..917f9ffd 100644
--- a/pango/pango.h
+++ b/pango/pango.h
@@ -39,6 +39,7 @@
 #include <pango/pango-glyph.h>
 #include <pango/pango-glyph-item.h>
 #include <pango/pango-gravity.h>
+#include <pango/pango-hbface.h>
 #include <pango/pango-item.h>
 #include <pango/pango-language.h>
 #include <pango/pango-layout.h>