diff --git a/src/hb-paint-extents.hh b/src/hb-paint-extents.hh
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+++ b/src/hb-paint-extents.hh
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+/*
+ * Copyright © 2022 Behdad Esfahbod
+ *
+ *  This is part of HarfBuzz, a text shaping library.
+ *
+ * Permission is hereby granted, without written agreement and without
+ * license or royalty fees, to use, copy, modify, and distribute this
+ * software and its documentation for any purpose, provided that the
+ * above copyright notice and the following two paragraphs appear in
+ * all copies of this software.
+ *
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
+ * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ */
+
+#ifndef HB_PAINT_EXTENTS_HH
+#define HB_PAINT_EXTENTS_HH
+
+#include "hb.hh"
+#include "hb-paint.h"
+
+
+typedef struct hb_extents_t
+{
+  hb_extents_t () {}
+  hb_extents_t (float xmin, float ymin, float xmax, float ymax) :
+    xmin (xmin), ymin (ymin), xmax (xmax), ymax (ymax) {}
+
+  bool is_empty () const { return xmin >= xmax || ymin >= ymax; }
+
+  void union_ (const hb_extents_t &o)
+  {
+    xmin = hb_min (xmin, o.xmin);
+    ymin = hb_min (ymin, o.ymin);
+    xmax = hb_max (xmax, o.xmax);
+    ymax = hb_max (ymax, o.ymax);
+  }
+
+  void intersect (const hb_extents_t &o)
+  {
+    xmin = hb_max (xmin, o.xmin);
+    ymin = hb_max (ymin, o.ymin);
+    xmax = hb_min (xmax, o.xmax);
+    ymax = hb_min (ymax, o.ymax);
+  }
+
+  float xmin = 0.f;
+  float ymin = 0.f;
+  float xmax = -1.f;
+  float ymax = -1.f;
+} hb_extents_t;
+
+typedef struct hb_transform_t
+{
+  hb_transform_t () {}
+  hb_transform_t (float xx, float yx,
+		  float xy, float yy,
+		  float x0, float y0) :
+    xx (xx), yx (yx), xy (xy), yy (yy), x0 (x0), y0 (y0) {}
+
+  void multiply (const hb_transform_t &o)
+  {
+    /* Copied from cairo, with "o" being "a" there and "this" being "b" there. */
+    hb_transform_t r;
+
+    r.xx = o.xx * xx + o.yx * xy;
+    r.yx = o.xx * yx + o.yx * yy;
+
+    r.xy = o.xy * xx + o.yy * xy;
+    r.yy = o.xy * yx + o.yy * yy;
+
+    r.x0 = o.x0 * xx + o.y0 * xy + x0;
+    r.y0 = o.x0 * yx + o.y0 * yy + y0;
+
+    *this = r;
+  }
+
+  void transform_distance (float &dx, float &dy)
+  {
+    float new_x = xx * dx + xy * dy;
+    float new_y = yx * dx + yy * dy;
+    dx = new_x;
+    dy = new_y;
+  }
+
+  void transform_point (float &x, float &y)
+  {
+    transform_distance (x, y);
+    x += x0;
+    y += y0;
+  }
+
+  void transform_extents (hb_extents_t extents)
+  {
+    float quad_x[4], quad_y[4];
+
+    quad_x[0] = extents.xmin;
+    quad_y[0] = extents.ymin;
+    quad_x[1] = extents.xmin;
+    quad_y[1] = extents.ymax;
+    quad_x[2] = extents.xmax;
+    quad_y[2] = extents.ymin;
+    quad_x[3] = extents.xmax;
+    quad_y[3] = extents.ymax;
+
+    for (unsigned i = 0; i < 4; i++)
+      transform_point (quad_x[i], quad_y[i]);
+
+    extents.xmin = extents.xmax = quad_x[0];
+    extents.ymin = extents.ymax = quad_y[0];
+
+    for (unsigned i = 1; i < 4; i++)
+    {
+      extents.xmin = hb_min (extents.xmin, quad_x[i]);
+      extents.ymin = hb_min (extents.ymin, quad_y[i]);
+      extents.xmax = hb_max (extents.xmax, quad_x[i]);
+      extents.ymax = hb_max (extents.ymax, quad_y[i]);
+    }
+  }
+
+  float xx = 1.f;
+  float yx = 0.f;
+  float xy = 0.f;
+  float yy = 1.f;
+  float x0 = 0.f;
+  float y0 = 0.f;
+} hb_transform_t;
+
+typedef struct hb_bounds_t
+{
+  enum status_t {
+    EMPTY,
+    BOUNDED,
+    UNBOUNDED,
+  };
+
+  hb_bounds_t (status_t status) : status (status) {}
+  hb_bounds_t (const hb_extents_t &extents) :
+    status (extents.is_empty () ? EMPTY : BOUNDED), extents (extents) {}
+
+  void union_ (const hb_bounds_t &o)
+  {
+    if (o.status == UNBOUNDED)
+      status = UNBOUNDED;
+    else if (o.status == BOUNDED)
+    {
+      if (status == EMPTY)
+	*this = o;
+      else if (status == BOUNDED)
+        extents.union_ (o.extents);
+    }
+  }
+
+  void intersect (const hb_bounds_t &o)
+  {
+    if (o.status == EMPTY)
+      status = EMPTY;
+    else if (o.status == BOUNDED)
+    {
+      if (status == UNBOUNDED)
+	*this = o;
+      else if (status == BOUNDED)
+      {
+        extents.intersect (o.extents);
+	if (extents.is_empty ())
+	  status = EMPTY;
+      }
+    }
+  }
+
+  status_t status;
+  hb_extents_t extents;
+} hb_bounds_t;
+
+typedef struct  hb_paint_extents_context_t hb_paint_extents_context_t;
+
+struct hb_paint_extents_context_t {
+
+  hb_paint_extents_context_t ()
+  {
+    clips.push (hb_bounds_t{hb_bounds_t::UNBOUNDED});
+    groups.push (hb_bounds_t{hb_bounds_t::EMPTY});
+    transforms.push (hb_transform_t{});
+  }
+
+  hb_extents_t get_extents ()
+  {
+    return groups.tail().extents;
+  }
+
+  bool is_bounded ()
+  {
+    return groups.tail().status != hb_bounds_t::UNBOUNDED;
+  }
+
+  void push_transform (const hb_transform_t &trans)
+  {
+    hb_transform_t r = transforms.tail ();
+    r.multiply (trans);
+    transforms.push (r);
+  }
+
+  void pop_transform ()
+  {
+    transforms.pop ();
+  }
+
+  void push_clip (hb_extents_t extents)
+  {
+    /* Transform extents and push a new clip. */
+    hb_transform_t &r = transforms.tail ();
+    r.transform_extents (extents);
+
+    hb_bounds_t b {extents};
+    clips.push (b);
+  }
+
+  void pop_clip ()
+  {
+    clips.pop ();
+  }
+
+  void push_group ()
+  {
+    groups.push (hb_bounds_t{hb_bounds_t::EMPTY});
+  }
+
+  void pop_group (hb_paint_composite_mode_t mode)
+  {
+    const hb_bounds_t src_bounds = groups.pop ();
+    hb_bounds_t &backdrop_bounds = groups.tail ();
+
+    // https://learn.microsoft.com/en-us/typography/opentype/spec/colr#format-32-paintcomposite
+    switch ((int) mode)
+    {
+      case HB_PAINT_COMPOSITE_MODE_CLEAR:
+	backdrop_bounds.status = hb_bounds_t::EMPTY;
+	break;
+      case HB_PAINT_COMPOSITE_MODE_SRC:
+      case HB_PAINT_COMPOSITE_MODE_SRC_OUT:
+	backdrop_bounds = src_bounds;
+	break;
+      case HB_PAINT_COMPOSITE_MODE_DEST:
+      case HB_PAINT_COMPOSITE_MODE_DEST_OUT:
+	break;
+      case HB_PAINT_COMPOSITE_MODE_SRC_IN:
+      case HB_PAINT_COMPOSITE_MODE_DEST_IN:
+	backdrop_bounds.intersect (src_bounds);
+	break;
+      default:
+	backdrop_bounds.union_ (src_bounds);
+	break;
+     }
+  }
+
+  void paint ()
+  {
+    const hb_bounds_t &clip = clips.tail ();
+    hb_bounds_t &group = groups.tail ();
+
+    group.union_ (clip);
+  }
+
+  hb_vector_t<hb_bounds_t> clips;
+  hb_vector_t<hb_bounds_t> groups;
+  hb_vector_t<hb_transform_t> transforms;
+};
+
+HB_INTERNAL hb_paint_funcs_t *
+hb_paint_extents_get_funcs ();
+
+
+#endif /* HB_PAINT_EXTENTS_HH */