[pango/pango2: 106/168] Add PangoHbFont

[Matthias Clasen <matthiasc src gnome org>]

commit 74cf20aebac9acabc9143d02c4c43ccc11b4cd54
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Oct 29 19:19:31 2021 -0400

    Add PangoHbFont
    
    This is a simple wrapper around hb_font_t.
    
    This is an attempt to make a font backend that does
    not depend on platform specifics and can be used in
    tests.

 pango/meson.build            |    2 +
 pango/pango-hbfont-private.h |   58 +++
 pango/pango-hbfont.c         | 1040 ++++++++++++++++++++++++++++++++++++++++++
 pango/pango-hbfont.h         |   50 ++
 pango/pango.h                |    1 +
 5 files changed, 1151 insertions(+)
---
diff --git a/pango/meson.build b/pango/meson.build
index 92db28e7..93eacf82 100644
--- a/pango/meson.build
+++ b/pango/meson.build
@@ -44,6 +44,7 @@ pango_sources = [
   'pango-hbface.c',
   'pango-hbfamily.c',
   'pango-generic-family.c',
+  'pango-hbfont.c',
 ]
 
 pango_headers = [
@@ -82,6 +83,7 @@ pango_headers = [
   'pango-types.h',
   'pango-utils.h',
   'pango-hbface.h',
+  'pango-hbfont.h',
 ]
 
 pango_gir_includes = [
diff --git a/pango/pango-hbfont-private.h b/pango/pango-hbfont-private.h
new file mode 100644
index 00000000..eb945dc2
--- /dev/null
+++ b/pango/pango-hbfont-private.h
@@ -0,0 +1,58 @@
+/*
+ * Copyright 2021 Red Hat, Inc.
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "pango-hbfont.h"
+#include "pango-hbface.h"
+#include "pango-font-private.h"
+
+#include <hb.h>
+
+
+typedef struct _HexBoxInfo HexBoxInfo;
+struct _HexBoxInfo
+{
+  PangoFont *font;
+  int rows;
+  double digit_width;
+  double digit_height;
+  double pad_x;
+  double pad_y;
+  double line_width;
+  double box_descent;
+  double box_height;
+};
+
+struct _PangoHbFont
+{
+  PangoFont parent_instance;
+
+  PangoHbFace *face;
+  int size; /* point size, scaled by PANGO_SCALE */
+  float dpi;
+  hb_feature_t *features;
+  unsigned int n_features;
+  hb_variation_t *variations;
+  unsigned int n_variations;
+  PangoGravity gravity;
+  PangoMatrix matrix;
+
+  HexBoxInfo *hex_box_info;
+};
diff --git a/pango/pango-hbfont.c b/pango/pango-hbfont.c
new file mode 100644
index 00000000..76423697
--- /dev/null
+++ b/pango/pango-hbfont.c
@@ -0,0 +1,1040 @@
+/* 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-hbfont-private.h"
+
+#include "pango-font-private.h"
+#include "pango-font-metrics-private.h"
+#include "pango-coverage-private.h"
+#include "pango-hbface-private.h"
+#include "pango-hbfamily-private.h"
+#include "pango-impl-utils.h"
+#include "pango-language-set-private.h"
+
+#include <hb-ot.h>
+
+/**
+ * PangoHbFont:
+ *
+ * `PangoHbFont` is a `PangoFont` implementation that wraps
+ * a `hb_font_t` object and implements all of the `PangoFont`
+ * functionality using HarfBuzz.
+ *
+ * In addition to a `PangoHbFace` and a size, a number of optional
+ * parameters can be tweaked when creating a `PangoHbFont`. First
+ * there are OpenType font features, which can be used to e.g.
+ * select Small Caps. If the face has variation axes, then
+ * coordinates for these axes can be provided. Finally, there are
+ * rendering parameters such as the dpi and the global transformation
+ * matrix.
+ */
+
+ /* {{{ Utilities */
+
+static int
+get_average_char_width (PangoFont  *font,
+                        const char *text)
+{
+  hb_font_t *hb_font = pango_font_get_hb_font (font);
+  int width = 0;
+
+  for (const char *p = text; *p; p = g_utf8_next_char (p))
+    {
+      gunichar wc;
+      hb_codepoint_t glyph;
+      PangoRectangle extents;
+
+      wc = g_utf8_get_char (p);
+      if (!hb_font_get_nominal_glyph (hb_font, wc, &glyph))
+        continue;
+
+      pango_font_get_glyph_extents (font, glyph, &extents, NULL);
+
+      width += extents.x + extents.width;
+    }
+
+  return width / pango_utf8_strwidth (text);
+}
+
+static void
+get_max_char_size (PangoFont  *font,
+                   const char *text,
+                   int        *width,
+                   int        *height)
+{
+  hb_font_t *hb_font = pango_font_get_hb_font (font);
+  int w = 0;
+  int h = 0;
+
+  for (const char *p = text; *p; p = g_utf8_next_char (p))
+    {
+      gunichar wc;
+      hb_codepoint_t glyph;
+      PangoRectangle extents;
+
+      wc = g_utf8_get_char (p);
+      if (!hb_font_get_nominal_glyph (hb_font, wc, &glyph))
+        continue;
+
+      pango_font_get_glyph_extents (font, glyph, &extents, NULL);
+
+      w = MAX (w, extents.x + extents.width);
+      h = MAX (h, extents.height);
+    }
+
+  if (width)
+    *width = w;
+
+  if (height)
+    *height = h;
+}
+
+static PangoFontMap *
+pango_hb_font_get_font_map (PangoFont *font)
+{
+  PangoHbFont *self = PANGO_HB_FONT (font);
+  PangoHbFamily *family = PANGO_HB_FAMILY (self->face->family);
+
+  return family->map;
+}
+
+static PangoVariant
+pango_variant_from_features (hb_feature_t *features,
+                             unsigned int  n_features)
+{
+  PangoVariant variant = PANGO_VARIANT_NORMAL;
+  gboolean all_caps = FALSE;
+
+  for (int i = 0; i < n_features; i++)
+    {
+      if (features[i].value != 1)
+        continue;
+
+      switch (features[i].tag)
+        {
+        case HB_TAG('s','m','c','p'):
+          if (all_caps)
+            variant = PANGO_VARIANT_ALL_SMALL_CAPS;
+          else
+            variant = PANGO_VARIANT_SMALL_CAPS;
+          break;
+        case HB_TAG('c','2','s','c'):
+          if (variant == PANGO_VARIANT_SMALL_CAPS)
+            variant = PANGO_VARIANT_ALL_SMALL_CAPS;
+          else
+            all_caps = TRUE;
+          break;
+        case HB_TAG('p','c','a','p'):
+          if (all_caps)
+            variant = PANGO_VARIANT_ALL_PETITE_CAPS;
+          else
+            variant = PANGO_VARIANT_PETITE_CAPS;
+          break;
+        case HB_TAG('c','2','p','c'):
+          if (variant == PANGO_VARIANT_PETITE_CAPS)
+            variant = PANGO_VARIANT_ALL_PETITE_CAPS;
+          else
+            all_caps = TRUE;
+          break;
+        case HB_TAG('u','n','i','c'):
+          variant = PANGO_VARIANT_UNICASE;
+          break;
+        case HB_TAG('t','i','t','l'):
+          variant = PANGO_VARIANT_TITLE_CAPS;
+          break;
+        default:
+          break;
+        }
+    }
+
+  return variant;
+}
+
+static void
+font_description_get_features (const PangoFontDescription *description,
+                               hb_feature_t               *features,
+                               unsigned int                length,
+                               unsigned int               *n_features)
+{
+
+#define ADD_FEATURE(name) \
+ features[*n_features].tag = HB_TAG (name[0], name[1], name[2], name[3]); \
+ features[*n_features].value = 1; \
+ features[*n_features].start = 0; \
+ features[*n_features].end = (unsigned int) -1; \
+ (*n_features)++
+
+  g_assert (length >= 2);
+
+  *n_features = 0;
+  switch (pango_font_description_get_variant (description))
+    {
+    case PANGO_VARIANT_SMALL_CAPS:
+      ADD_FEATURE ("smcp");
+      break;
+    case PANGO_VARIANT_ALL_SMALL_CAPS:
+      ADD_FEATURE ("smcp");
+      ADD_FEATURE ("c2sc");
+      break;
+    case PANGO_VARIANT_PETITE_CAPS:
+      ADD_FEATURE ("pcap");
+      break;
+    case PANGO_VARIANT_ALL_PETITE_CAPS:
+      ADD_FEATURE ("pcap");
+      ADD_FEATURE ("c2pc");
+      break;
+    case PANGO_VARIANT_UNICASE:
+      ADD_FEATURE ("unic");
+      break;
+    case PANGO_VARIANT_TITLE_CAPS:
+      ADD_FEATURE ("titl");
+      break;
+    case PANGO_VARIANT_NORMAL:
+      break;
+    default:
+      g_assert_not_reached ();
+    }
+
+#undef ADD_FEATURE
+}
+
+static unsigned int
+count_variations (const char *string)
+{
+  unsigned int n;
+  const char *p;
+
+  n = 1;
+  p = string;
+  while ((p = strchr (p, ',')) != NULL)
+    n++;
+
+  return n;
+}
+
+static void
+parse_variations (const char     *str,
+                  hb_variation_t *variations,
+                  unsigned int    length,
+                  unsigned int   *n_variations)
+{
+  const char *p;
+
+  *n_variations = 0;
+
+  p = str;
+  while (p && *p && *n_variations < length)
+    {
+      const char *end = strchr (p, ',');
+      if (hb_variation_from_string (p, end ? end - p: -1, &variations[*n_variations]))
+        (*n_variations)++;
+      p = end ? end + 1 : NULL;
+    }
+}
+
+static char *
+variations_to_string (hb_variation_t *variations,
+                      unsigned int    n_variations)
+{
+  GString *s;
+  char buf[128];
+
+  s = g_string_new ("");
+
+  for (unsigned int i = 0; i < n_variations; i++)
+    {
+      hb_variation_to_string (&variations[i], buf, sizeof (buf));
+      if (s->len > 0)
+        g_string_append_c (s, ',');
+      g_string_append (s, buf);
+    }
+
+  return g_string_free (s, FALSE);
+}
+
+static inline void
+replace_variation (hb_variation_t       *values,
+                   unsigned int         *len,
+                   const hb_variation_t *v)
+{
+  for (int i = 0; i < *len; i++)
+    {
+      if (values[i].tag == v->tag)
+        {
+          values[i].value = v->value;
+          return;
+        }
+    }
+
+  values[(*len)++] = *v;
+}
+
+static unsigned int
+merge_variations (const hb_variation_t *v1,
+                  unsigned int          l1,
+                  const hb_variation_t *v2,
+                  unsigned int          l2,
+                  hb_variation_t       *v,
+                  unsigned int          l)
+{
+  unsigned int len = 0;
+
+  for (int i = 0; i < l1; i++)
+    replace_variation (v, &len, &v1[i]);
+
+  for (int i = 0; i < l2; i++)
+    replace_variation (v, &len, &v2[i]);
+
+  return len;
+}
+
+static inline void
+collect_variation (hb_variation_t        *variation,
+                   unsigned int           n_axes,
+                   hb_ot_var_axis_info_t *axes,
+                   float                 *coords)
+{
+  for (int j = 0; j < n_axes; j++)
+    {
+      if (axes[j].tag == variation->tag)
+        {
+          coords[axes[j].axis_index] = variation->value;
+          break;
+        }
+    }
+}
+
+static inline void
+collect_variations (hb_variation_t        *variations,
+                    unsigned int           n_variations,
+                    unsigned int           n_axes,
+                    hb_ot_var_axis_info_t *axes,
+                    float                 *coords)
+{
+  for (int i = 0; i < n_variations; i++)
+    collect_variation (&variations[i], n_axes, axes, coords);
+}
+
+/* }}} */
+/* {{{ hex box sizing */
+
+/* This code needs to stay in sync with the hexbox rendering code in pangocairo-render.c */
+static HexBoxInfo *
+create_hex_box_info (PangoHbFont *self)
+{
+  const char hexdigits[] = "0123456789ABCDEF";
+  hb_font_t *hb_font;
+  PangoFont *mini_font;
+  HexBoxInfo *hbi;
+  int rows;
+  double pad;
+  int width = 0;
+  int height = 0;
+  hb_font_extents_t font_extents;
+  double font_ascent, font_descent;
+  double mini_size;
+  PangoFontDescription *desc;
+  PangoContext *context;
+  PangoFontMap *map;
+
+  map = pango_hb_font_get_font_map (PANGO_FONT (self));
+
+  if (!map)
+    return NULL;
+
+  desc = pango_font_describe_with_absolute_size (PANGO_FONT (self));
+  hb_font = pango_font_get_hb_font (PANGO_FONT (self));
+
+  /* Create mini_font description */
+
+  /* We inherit most font properties for the mini font.
+   * Just change family and size, so you get bold
+   * hex digits in the hexbox for a bold font.
+   */
+
+  /* We should rotate the box, not glyphs */
+  pango_font_description_unset_fields (desc, PANGO_FONT_MASK_GRAVITY);
+
+  pango_font_description_set_family_static (desc, "monospace");
+
+  rows = 2;
+  mini_size = self->size / 2.2;
+
+  if (mini_size < 6.0)
+    {
+      rows = 1;
+      mini_size = MIN (MAX (self->size - 1, 0), 6.0);
+    }
+
+  pango_font_description_set_size (desc, mini_size);
+
+  /* Load mini_font */
+  context = pango_font_map_create_context (map);
+  pango_context_set_matrix (context, &self->matrix);
+  pango_context_set_language (context, pango_script_get_sample_language (G_UNICODE_SCRIPT_LATIN));
+
+  mini_font = pango_font_map_load_font (map, context, desc);
+
+  g_object_unref (context);
+
+  pango_font_description_free (desc);
+
+  get_max_char_size (mini_font, hexdigits, &width, &height);
+
+  hb_font_get_extents_for_direction (hb_font, HB_DIRECTION_LTR, &font_extents);
+  font_ascent = font_extents.ascender / (double) PANGO_SCALE;
+  font_descent = - font_extents.descender / (double) PANGO_SCALE;
+
+  pad = (font_ascent + font_descent) / 43.;
+  pad = MIN (pad, mini_size / (double) PANGO_SCALE);
+
+  hbi = g_new (HexBoxInfo, 1);
+  hbi->font = mini_font;
+  hbi->rows = rows;
+
+  hbi->digit_width  = width / (double) PANGO_SCALE;
+  hbi->digit_height = height / (double) PANGO_SCALE;
+
+  hbi->pad_x = pad;
+  hbi->pad_y = pad;
+
+  hbi->line_width = MIN (hbi->pad_x, hbi->pad_y);
+
+  hbi->box_height = 3 * hbi->pad_y + rows * (hbi->pad_y + hbi->digit_height);
+
+  if (rows == 1 || hbi->box_height <= font_ascent)
+    hbi->box_descent = 2 * hbi->pad_y;
+  else if (hbi->box_height <= font_ascent + font_descent - 2 * hbi->pad_y)
+    hbi->box_descent = 2 * hbi->pad_y + hbi->box_height - font_ascent;
+  else
+    hbi->box_descent = font_descent * hbi->box_height / (font_ascent + font_descent);
+
+  return hbi;
+}
+
+static void
+get_space_extents (PangoHbFont    *self,
+                   PangoRectangle *ink_rect,
+                   PangoRectangle *logical_rect)
+{
+  hb_font_t *hb_font = pango_font_get_hb_font (PANGO_FONT (self));
+  int width;
+  hb_direction_t direction;
+  hb_font_extents_t font_extents;
+
+  direction = PANGO_GRAVITY_IS_VERTICAL (self->gravity)
+              ? HB_DIRECTION_TTB
+              : HB_DIRECTION_LTR;
+
+  hb_font_get_extents_for_direction (hb_font, direction, &font_extents);
+
+  /* See https://docs.microsoft.com/en-us/typography/develop/character-design-standards/whitespace */
+
+  width = self->size / 4;
+
+  if (ink_rect)
+    {
+      ink_rect->x = ink_rect->y = ink_rect->height = 0;
+      ink_rect->width = width;
+    }
+
+  if (logical_rect)
+    {
+      logical_rect->x = 0;
+      logical_rect->y = - font_extents.ascender;
+      logical_rect->height = font_extents.ascender - font_extents.descender;
+      logical_rect->width = width;
+    }
+}
+
+static void
+get_glyph_extents_missing (PangoHbFont    *self,
+                           PangoGlyph      glyph,
+                           PangoRectangle *ink_rect,
+                           PangoRectangle *logical_rect)
+{
+  gunichar ch;
+  int rows, cols;
+  HexBoxInfo *hbi;
+
+  ch = glyph & ~PANGO_GLYPH_UNKNOWN_FLAG;
+
+  if (!self->hex_box_info)
+    self->hex_box_info = create_hex_box_info (self);
+
+  if (ch == 0x20 || ch == 0x2423)
+    {
+      get_space_extents (self, ink_rect, logical_rect);
+      return;
+    }
+
+  hbi = self->hex_box_info;
+
+  if (G_UNLIKELY (glyph == PANGO_GLYPH_INVALID_INPUT || ch > 0x10FFFF))
+    {
+      rows = hbi->rows;
+      cols = 1;
+    }
+  else if (pango_get_ignorable_size (ch, &rows, &cols))
+    {
+      /* We special-case ignorables when rendering hex boxes */
+    }
+  else
+    {
+      rows = hbi->rows;
+      cols = (ch > 0xffff ? 6 : 4) / rows;
+    }
+
+  if (ink_rect)
+    {
+      ink_rect->x = PANGO_SCALE * hbi->pad_x;
+      ink_rect->y = PANGO_SCALE * (hbi->box_descent - hbi->box_height);
+      ink_rect->width = PANGO_SCALE * (3 * hbi->pad_x + cols * (hbi->digit_width + hbi->pad_x));
+      ink_rect->height = PANGO_SCALE * hbi->box_height;
+    }
+
+  if (logical_rect)
+    {
+      logical_rect->x = 0;
+      logical_rect->y = PANGO_SCALE * (hbi->box_descent - (hbi->box_height + hbi->pad_y));
+      logical_rect->width = PANGO_SCALE * (5 * hbi->pad_x + cols * (hbi->digit_width + hbi->pad_x));
+      logical_rect->height = PANGO_SCALE * (hbi->box_height + 2 * hbi->pad_y);
+    }
+}
+
+ /* }}} */
+/* {{{ PangoFont implementation */
+
+struct _PangoHbFontClass
+{
+  PangoFontClass parent_class;
+};
+
+G_DEFINE_TYPE (PangoHbFont, pango_hb_font, PANGO_TYPE_FONT)
+
+static void
+pango_hb_font_init (PangoHbFont *self)
+{
+  self->gravity = PANGO_GRAVITY_AUTO;
+  self->matrix = (PangoMatrix) PANGO_MATRIX_INIT;
+}
+
+static void
+hex_box_info_destroy (HexBoxInfo *hex_box_info)
+{
+  g_object_unref (hex_box_info->font);
+  g_free (hex_box_info);
+}
+
+static void
+pango_hb_font_finalize (GObject *object)
+{
+  PangoHbFont *self = PANGO_HB_FONT (object);
+
+  g_object_unref (self->face);
+  g_free (self->variations);
+  g_clear_pointer (&self->hex_box_info, hex_box_info_destroy);
+
+  G_OBJECT_CLASS (pango_hb_font_parent_class)->finalize (object);
+}
+
+static PangoFontDescription *
+pango_hb_font_describe (PangoFont *font)
+{
+  PangoHbFont *self = PANGO_HB_FONT (font);
+  PangoFontDescription *desc;
+  PangoVariant variant;
+
+  desc = pango_font_face_describe (PANGO_FONT_FACE (self->face));
+  pango_font_description_set_gravity (desc, self->gravity);
+  variant = pango_variant_from_features (self->features, self->n_features);
+  if (variant != PANGO_VARIANT_NORMAL)
+    pango_font_description_set_variant (desc, variant);
+  if (self->n_variations > 0)
+    {
+      hb_variation_t *variations;
+      unsigned int n_variations;
+      char *str;
+
+      if (self->face->n_variations > 0)
+        {
+           variations = g_alloca (sizeof (hb_variation_t) * (self->n_variations + self->face->n_variations));
+           n_variations = merge_variations (self->face->variations, self->face->n_variations,
+                                            self->variations, self->n_variations,
+                                            variations, self->n_variations + self->face->n_variations);
+        }
+      else
+        {
+          variations = self->variations;
+          n_variations = self->n_variations;
+        }
+
+      str = variations_to_string (variations, n_variations);
+      pango_font_description_set_variations (desc, str);
+      g_free (str);
+    }
+  pango_font_description_set_size (desc, self->size);
+
+  return desc;
+}
+
+static PangoFontDescription *
+pango_hb_font_describe_absolute (PangoFont *font)
+{
+  PangoHbFont *self = PANGO_HB_FONT (font);
+  PangoFontDescription *desc;
+
+  desc = pango_hb_font_describe (font);
+  pango_font_description_set_absolute_size (desc, self->size * self->dpi / 72.);
+
+  return desc;
+}
+
+static PangoCoverage *
+pango_hb_font_get_coverage (PangoFont     *font,
+                            PangoLanguage *language G_GNUC_UNUSED)
+{
+  PangoHbFont *self = PANGO_HB_FONT (font);
+
+  return pango_coverage_new_for_hb_face (pango_hb_face_get_hb_face (self->face));
+}
+
+static void
+pango_hb_font_get_glyph_extents (PangoFont      *font,
+                                 PangoGlyph      glyph,
+                                 PangoRectangle *ink_rect,
+                                 PangoRectangle *logical_rect)
+{
+  PangoHbFont *self = PANGO_HB_FONT (font);
+  hb_font_t *hb_font = pango_font_get_hb_font (font);
+  hb_glyph_extents_t extents;
+  hb_direction_t direction;
+  hb_font_extents_t font_extents;
+
+  direction = PANGO_GRAVITY_IS_VERTICAL (self->gravity)
+              ? HB_DIRECTION_TTB
+              : HB_DIRECTION_LTR;
+
+  hb_font_get_extents_for_direction (hb_font, direction, &font_extents);
+
+  if (glyph == PANGO_GLYPH_EMPTY)
+    {
+      if (ink_rect)
+        ink_rect->x = ink_rect->y = ink_rect->width = ink_rect->height = 0;
+
+      if (logical_rect)
+        {
+          logical_rect->x = logical_rect->width = 0;
+          logical_rect->y = - font_extents.ascender;
+          logical_rect->height = font_extents.ascender - font_extents.descender;
+        }
+
+      return;
+    }
+  else if (glyph & PANGO_GLYPH_UNKNOWN_FLAG)
+    {
+      get_glyph_extents_missing (self, glyph, ink_rect, logical_rect);
+
+      return;
+    }
+
+  hb_font_get_glyph_extents (hb_font, glyph, &extents);
+
+  if (ink_rect)
+    {
+      PangoRectangle r;
+      PangoMatrix m = PANGO_MATRIX_INIT;
+
+      r.x = extents.x_bearing;
+      r.y = - extents.y_bearing;
+      r.width = extents.width;
+      r.height = - extents.height;
+
+      if (self->face->matrix)
+        {
+          m.xx = self->face->matrix->xx;
+          m.yx = - self->face->matrix->yx;
+          m.xy = - self->face->matrix->xy;
+          m.yy = self->face->matrix->yy;
+        }
+
+      pango_matrix_transform_rectangle (&m, &r);
+
+      switch (self->gravity)
+        {
+        case PANGO_GRAVITY_AUTO:
+        case PANGO_GRAVITY_SOUTH:
+          ink_rect->x = r.x;
+          ink_rect->y = r.y;
+          ink_rect->width = r.width;
+          ink_rect->height = r.height;
+          break;
+        case PANGO_GRAVITY_NORTH:
+          ink_rect->x = - r.x;
+          ink_rect->y = - r.y;
+          ink_rect->width = - r.width;
+          ink_rect->height = - r.height;
+          break;
+        case PANGO_GRAVITY_EAST:
+          ink_rect->x = r.y;
+          ink_rect->y = - r.x - r.width;
+          ink_rect->width = r.height;
+          ink_rect->height = r.width;
+          break;
+        case PANGO_GRAVITY_WEST:
+          ink_rect->x = - r.y - r.height;
+          ink_rect->y = r.x;
+          ink_rect->width = r.height;
+          ink_rect->height = r.width;
+          break;
+        default:
+          g_assert_not_reached ();
+        }
+
+      if (PANGO_GRAVITY_IS_IMPROPER (self->gravity))
+        {
+          PangoMatrix matrix = (PangoMatrix) PANGO_MATRIX_INIT;
+          pango_matrix_scale (&matrix, -1, -1);
+          pango_matrix_transform_rectangle (&matrix, ink_rect);
+        }
+    }
+
+  if (logical_rect)
+    {
+      hb_position_t h_advance;
+      hb_font_extents_t extents;
+
+      h_advance = hb_font_get_glyph_h_advance (hb_font, glyph);
+      hb_font_get_h_extents (hb_font, &extents);
+
+      logical_rect->x = 0;
+      logical_rect->height = extents.ascender - extents.descender;
+
+      switch (self->gravity)
+        {
+        case PANGO_GRAVITY_AUTO:
+        case PANGO_GRAVITY_SOUTH:
+          logical_rect->y = - extents.ascender;
+          logical_rect->width = h_advance;
+          break;
+        case PANGO_GRAVITY_NORTH:
+          logical_rect->y = extents.descender;
+          logical_rect->width = h_advance;
+          break;
+        case PANGO_GRAVITY_EAST:
+          logical_rect->y = - logical_rect->height / 2;
+          logical_rect->width = logical_rect->height;
+          break;
+        case PANGO_GRAVITY_WEST:
+          logical_rect->y = - logical_rect->height / 2;
+          logical_rect->width = - logical_rect->height;
+          break;
+        default:
+          g_assert_not_reached ();
+        }
+
+      if (PANGO_GRAVITY_IS_IMPROPER (self->gravity))
+        {
+          logical_rect->height = - logical_rect->height;
+          logical_rect->y = - logical_rect->y;
+        }
+    }
+}
+
+static PangoFontMetrics *
+pango_hb_font_get_metrics (PangoFont     *font,
+                           PangoLanguage *language)
+{
+  hb_font_t *hb_font = pango_font_get_hb_font (font);
+  PangoFontMetrics *metrics;
+  hb_font_extents_t extents;
+  hb_position_t position;
+
+  metrics = pango_font_metrics_new ();
+
+  hb_font_get_extents_for_direction (hb_font, HB_DIRECTION_LTR, &extents);
+
+  metrics->descent = - extents.descender;
+  metrics->ascent = extents.ascender;
+  metrics->height = extents.ascender - extents.descender + extents.line_gap;
+
+  if (hb_ot_metrics_get_position (hb_font, HB_OT_METRICS_TAG_UNDERLINE_SIZE, &position) && position != 0)
+    metrics->underline_thickness = position;
+  else
+    metrics->underline_thickness = PANGO_SCALE;
+
+  if (hb_ot_metrics_get_position (hb_font, HB_OT_METRICS_TAG_UNDERLINE_OFFSET, &position) && position != 0)
+    metrics->underline_position = position;
+  else
+    metrics->underline_position = - PANGO_SCALE;
+
+  if (hb_ot_metrics_get_position (hb_font, HB_OT_METRICS_TAG_STRIKEOUT_SIZE, &position) && position != 0)
+    metrics->strikethrough_thickness = position;
+  else
+    metrics->strikethrough_thickness = PANGO_SCALE;
+
+  if (hb_ot_metrics_get_position (hb_font, HB_OT_METRICS_TAG_STRIKEOUT_OFFSET, &position) && position != 0)
+    metrics->strikethrough_position = position;
+  else
+    metrics->strikethrough_position = metrics->ascent / 2;
+
+  metrics->approximate_char_width = get_average_char_width (font, pango_language_get_sample_string 
(language));
+  get_max_char_size (font, "0123456789", &metrics->approximate_digit_width, NULL);
+
+  return metrics;
+}
+
+static hb_font_t *
+pango_hb_font_create_hb_font (PangoFont *font)
+{
+  PangoHbFont *self = PANGO_HB_FONT (font);
+  hb_face_t *hb_face;
+  hb_font_t *hb_font;
+  double x_scale, y_scale;
+  unsigned int n_axes;
+  hb_ot_var_axis_info_t *axes;
+  float *coords;
+  int size;
+
+  hb_face = pango_hb_face_get_hb_face (self->face);
+  hb_font = hb_font_create (hb_face);
+
+  size = self->size * self->dpi / 72.f;
+  x_scale = self->face->x_scale;
+  y_scale = self->face->y_scale;
+
+  if (PANGO_GRAVITY_IS_IMPROPER (self->gravity))
+    {
+      x_scale = - x_scale;
+      y_scale = - y_scale;
+    }
+
+  hb_font_set_scale (hb_font, size * x_scale, size * y_scale);
+  hb_font_set_ptem (hb_font, self->size / PANGO_SCALE);
+
+#if HB_VERSION_ATLEAST (3, 3, 0)
+  hb_font_set_synthetic_slant (hb_font, pango_matrix_get_slant_ratio (self->face->matrix));
+#endif
+
+  if (self->face->instance_id >= 0)
+    hb_font_set_var_named_instance (hb_font, self->face->instance_id);
+
+  if (self->n_variations > 0 || self->face->n_variations > 0)
+    {
+      n_axes = hb_ot_var_get_axis_count (self->face->face);
+      axes = g_alloca (sizeof (hb_ot_var_axis_info_t) * n_axes);
+      coords = g_alloca (sizeof (float) * n_axes);
+
+      hb_ot_var_get_axis_infos (hb_face, 0, &n_axes, axes);
+
+      if (self->face->instance_id >= 0)
+        hb_ot_var_named_instance_get_design_coords (self->face->face, self->face->instance_id, &n_axes, 
coords);
+      else
+        {
+          for (int i = 0; i < n_axes; i++)
+            coords[axes[i].axis_index] = axes[i].default_value;
+        }
+
+      collect_variations (self->face->variations, self->face->n_variations, n_axes, axes, coords);
+      collect_variations (self->variations, self->n_variations, n_axes, axes, coords);
+
+      hb_font_set_var_coords_design (hb_font, coords, n_axes);
+    }
+
+  return hb_font;
+}
+
+static gboolean
+pango_hb_font_has_char (PangoFont *font,
+                        gunichar   wc)
+{
+  hb_font_t *hb_font = pango_font_get_hb_font (font);
+  hb_codepoint_t glyph;
+
+  return hb_font_get_nominal_glyph (hb_font, wc, &glyph);
+}
+
+static PangoFontFace *
+pango_hb_font_get_face (PangoFont *font)
+{
+  PangoHbFont *self = PANGO_HB_FONT (font);
+
+  return PANGO_FONT_FACE (self->face);
+}
+
+static void
+pango_hb_font_get_matrix (PangoFont   *font,
+                          PangoMatrix *matrix)
+{
+  PangoHbFont *self = PANGO_HB_FONT (font);
+
+  if (self->face->matrix)
+    {
+      *matrix = *self->face->matrix;
+      pango_matrix_scale (matrix, self->face->x_scale, self->face->y_scale);
+    }
+  else
+    *matrix = (PangoMatrix) PANGO_MATRIX_INIT;
+}
+
+static void
+pango_hb_font_get_features (PangoFont    *font,
+                            hb_feature_t *features,
+                            guint         len,
+                            guint        *num_features)
+{
+  PangoHbFont *self = PANGO_HB_FONT (font);
+
+  *num_features = MIN (len, self->n_features);
+  memcpy (features, self->features, sizeof (hb_feature_t) * *num_features);
+}
+
+static void
+pango_hb_font_class_init (PangoHbFontClass *class)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+  PangoFontClass *font_class = PANGO_FONT_CLASS (class);
+
+  object_class->finalize = pango_hb_font_finalize;
+
+  font_class->describe = pango_hb_font_describe;
+  font_class->describe_absolute = pango_hb_font_describe_absolute;
+  font_class->get_coverage = pango_hb_font_get_coverage;
+  font_class->get_glyph_extents = pango_hb_font_get_glyph_extents;
+  font_class->get_metrics = pango_hb_font_get_metrics;
+  font_class->get_font_map = pango_hb_font_get_font_map;
+  font_class->create_hb_font = pango_hb_font_create_hb_font;
+  font_class->get_features = pango_hb_font_get_features;
+  font_class->has_char = pango_hb_font_has_char;
+  font_class->get_face = pango_hb_font_get_face;
+  font_class->get_matrix = pango_hb_font_get_matrix;
+}
+
+/* }}} */
+ /* {{{ Public API */
+
+/**
+ * pango_hb_font_new:
+ * @face: the `PangoHbFace` to use
+ * @size: the desired size in points, scaled by `PANGO_SCALE`
+ * @features: (nullable) (array length=n_features): OpenType font features to use for this font
+ * @n_features: length of @features
+ * @variations: (nullable) (array length=n_variations): font variations to apply
+ * @n_variations: length of @variations
+ * @gravity: the gravity to use when rendering
+ * @dpi: the dpi used when rendering
+ * @matrix: (nullable): transformation matrix to use when rendering
+ *
+ * Creates a new `PangoHbFont`.
+ *
+ * Returns: a newly created `PangoHbFont`
+ */
+PangoHbFont *
+pango_hb_font_new (PangoHbFace       *face,
+                   int                size,
+                   hb_feature_t      *features,
+                   unsigned int       n_features,
+                   hb_variation_t    *variations,
+                   unsigned int       n_variations,
+                   PangoGravity       gravity,
+                   float              dpi,
+                   const PangoMatrix *matrix)
+{
+  PangoHbFont *self;
+
+  self = g_object_new (PANGO_TYPE_HB_FONT, NULL);
+
+  self->face = g_object_ref (face);
+
+  self->size = size;
+  self->dpi = dpi;
+  self->features = g_memdup2 (features, sizeof (hb_feature_t) * n_features);
+  self->n_features = n_features;
+  self->variations = g_memdup2 (variations, sizeof (hb_variation_t) * n_variations);
+  self->n_variations = n_variations;
+  if (gravity != PANGO_GRAVITY_AUTO)
+    self->gravity = gravity;
+  if (matrix)
+    self->matrix = *matrix;
+
+  return self;
+}
+
+/**
+ * pango_hb_font_new_for_description:
+ * @face: the `PangoHbFace` to use
+ * @description: a `PangoFontDescription`
+ * @dpi: the dpi used when rendering
+ * @matrix: (nullable): transformation matrix to use when rendering
+ *
+ * Creates a new `PangoHbFont` with size, features, variations and
+ * gravity taken from a font description.
+ *
+ * Returns: a newly created `PangoHbFont`
+ */
+PangoHbFont *
+pango_hb_font_new_for_description (PangoHbFace                *face,
+                                   const PangoFontDescription *description,
+                                   float                       dpi,
+                                   const PangoMatrix          *matrix)
+{
+  int size;
+  hb_feature_t features[10];
+  unsigned int n_features;
+  hb_variation_t *variations;
+  unsigned int n_variations;
+  unsigned int length;
+  PangoGravity gravity;
+  const char *str;
+
+  if (pango_font_description_get_size_is_absolute (description))
+    size = pango_font_description_get_size (description) * 72. / dpi;
+  else
+    size = pango_font_description_get_size (description);
+
+  font_description_get_features (description, features, G_N_ELEMENTS (features), &n_features);
+
+  if ((pango_font_description_get_set_fields (description) & PANGO_FONT_MASK_VARIATIONS) != 0)
+    {
+      str = pango_font_description_get_variations (description);
+      length = count_variations (str);
+      variations = g_alloca (sizeof (hb_variation_t) * length);
+      parse_variations (str, variations, length, &n_variations);
+    }
+  else
+    {
+      variations = NULL;
+      n_variations = 0;
+    }
+
+  if ((pango_font_description_get_set_fields (description) & PANGO_FONT_MASK_GRAVITY) != 0 &&
+      pango_font_description_get_gravity (description) != PANGO_GRAVITY_SOUTH)
+    gravity = pango_font_description_get_gravity (description);
+  else
+    gravity = PANGO_GRAVITY_AUTO;
+
+  return pango_hb_font_new (face, size, features, n_features, variations, n_variations, gravity, dpi, 
matrix);
+}
+
+/* }}} */
+
+/* vim:set foldmethod=marker expandtab: */
diff --git a/pango/pango-hbfont.h b/pango/pango-hbfont.h
new file mode 100644
index 00000000..8ff0a650
--- /dev/null
+++ b/pango/pango-hbfont.h
@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2021 Matthias Clasen
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <pango/pango-types.h>
+#include <pango/pango-font.h>
+#include <pango/pango-hbface.h>
+#include <hb.h>
+
+G_BEGIN_DECLS
+
+#define PANGO_TYPE_HB_FONT      (pango_hb_font_get_type ())
+
+PANGO_AVAILABLE_IN_ALL
+PANGO_DECLARE_INTERNAL_TYPE (PangoHbFont, pango_hb_font, PANGO, HB_FONT, PangoFont)
+
+PANGO_AVAILABLE_IN_ALL
+PangoHbFont *           pango_hb_font_new                       (PangoHbFace                    *face,
+                                                                 int                             size,
+                                                                 hb_feature_t                   *features,
+                                                                 unsigned int                    n_features,
+                                                                 hb_variation_t                 *variations,
+                                                                 unsigned int                    
n_variations,
+                                                                 PangoGravity                    gravity,
+                                                                 float                           dpi,
+                                                                 const PangoMatrix              *matrix);
+
+PANGO_AVAILABLE_IN_ALL
+PangoHbFont *           pango_hb_font_new_for_description       (PangoHbFace                    *face,
+                                                                 const PangoFontDescription     *description,
+                                                                 float                           dpi,
+                                                                 const PangoMatrix              *matrix);
+G_END_DECLS
diff --git a/pango/pango.h b/pango/pango.h
index 128950a0..080e98bd 100644
--- a/pango/pango.h
+++ b/pango/pango.h
@@ -43,6 +43,7 @@
 #include <pango/pango-glyph-item.h>
 #include <pango/pango-gravity.h>
 #include <pango/pango-hbface.h>
+#include <pango/pango-hbfont.h>
 #include <pango/pango-item.h>
 #include <pango/pango-language.h>
 #include <pango/pango-layout.h>