diff --git a/tests/cow_transparent.png b/tests/cow_transparent.png
new file mode 100644
index 0000000..912ee09
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diff --git a/tests/gradient.png b/tests/gradient.png
new file mode 100644
index 0000000..0c8605c
Binary files /dev/null and b/tests/gradient.png differ
diff --git a/tests/subsurface_1.png b/tests/subsurface_1.png
new file mode 100644
index 0000000..1a3542d
Binary files /dev/null and b/tests/subsurface_1.png differ
diff --git a/tests/subsurface_1_damaged.png b/tests/subsurface_1_damaged.png
new file mode 100644
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diff --git a/tests/subsurface_base.png b/tests/subsurface_base.png
new file mode 100644
index 0000000..15010b8
Binary files /dev/null and b/tests/subsurface_base.png differ
diff --git a/tests/subsurface_damage.png b/tests/subsurface_damage.png
new file mode 100644
index 0000000..0155a8d
Binary files /dev/null and b/tests/subsurface_damage.png differ
diff --git a/tests/subsurface_test.c b/tests/subsurface_test.c
new file mode 100644
index 0000000..cb57729
--- /dev/null
+++ b/tests/subsurface_test.c
@@ -0,0 +1,560 @@
+/* Tests for the Wayland compositor running on the X server.
+
+Copyright (C) 2022 to various contributors.
+
+This file is part of 12to11.
+
+12to11 is free software: you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the
+Free Software Foundation, either version 3 of the License, or (at your
+option) any later version.
+
+12to11 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 General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with 12to11.  If not, see <https://www.gnu.org/licenses/>.  */
+
+#include "test_harness.h"
+#include "viewporter.h"
+
+/* Tests for subsurfaces.  */
+
+enum test_kind
+  {
+    MAP_WINDOW_KIND,
+    SUBSURFACE_UNDER_KIND,
+    SUBSURFACE_OVER_KIND,
+    SUBSURFACE_MOVE_KIND,
+    SUBSURFACE_STACKING_KIND,
+    SUBSURFACE_TREE_KIND,
+  };
+
+static const char *test_names[] =
+  {
+    "map_window",
+    "subsurface_under",
+    "subsurface_over",
+    "subsurface_move",
+    "subsurface_stacking",
+    "subsurface_tree",
+  };
+
+struct test_subsurface
+{
+  /* The subsurface itself.  */
+  struct wl_subsurface *subsurface;
+
+  /* The associated surface.  */
+  struct wl_surface *surface;
+};
+
+#define LAST_TEST       SUBSURFACE_TREE_KIND
+
+/* The display.  */
+static struct test_display *display;
+
+/* The subcompositor interface.  */
+static struct wl_subcompositor *subcompositor;
+
+/* Test interfaces.  */
+static struct test_interface test_interfaces[] =
+  {
+    { "wl_subcompositor", &subcompositor, &wl_subcompositor_interface, 1, },
+  };
+
+/* The test surface window.  */
+static Window test_surface_window;
+
+/* The test surface and Wayland surface.  */
+static struct test_surface *test_surface;
+static struct wl_surface *wayland_surface;
+
+/* Various subsurfaces.  */
+static struct test_subsurface *subsurfaces[4];
+
+/* Various buffers.  */
+static struct wl_buffer *subsurface_base_png;
+static struct wl_buffer *subsurface_damage_png;
+static struct wl_buffer *subsurface_1_png;
+static struct wl_buffer *subsurface_1_damaged_png;
+static struct wl_buffer *subsurface_transparency_png;
+static struct wl_buffer *cow_transparent_png;
+static struct wl_buffer *gradient_png;
+
+/* The test image ID.  */
+static uint32_t current_test_image;
+
+
+
+/* Forward declarations.  */
+static void wait_frame_callback (struct wl_surface *);
+
+
+
+static void
+sleep_or_verify (void)
+{
+#ifndef INSPECTION
+  char *dump_name;
+#endif
+
+#ifdef INSPECTION
+  /* Sleep for 1 second so the human can see what is happening.  */
+  sleep (1);
+#else
+  if (asprintf (&dump_name, "subsurface_test_%"PRIu32".dump",
+		++current_test_image) < 0)
+    die ("asprintf");
+
+  verify_image_data (display, test_surface_window, dump_name);
+  free (dump_name);
+#endif
+}
+
+static void
+submit_surface_opaque_region (struct wl_surface *surface,
+			      int x, int y, int width, int height)
+{
+  struct wl_region *region;
+
+  region = wl_compositor_create_region (display->compositor);
+  wl_region_add (region, x, y, width, height);
+  wl_surface_set_opaque_region (surface, region);
+  wl_region_destroy (region);
+}
+
+static struct test_subsurface *
+make_test_subsurface (void)
+{
+  struct test_subsurface *subsurface;
+
+  subsurface = malloc (sizeof *subsurface);
+
+  if (!subsurface)
+    goto error_1;
+
+  subsurface->surface
+    = wl_compositor_create_surface (display->compositor);
+
+  if (!subsurface->surface)
+    goto error_2;
+
+  subsurface->subsurface
+    = wl_subcompositor_get_subsurface (subcompositor,
+				       subsurface->surface,
+				       wayland_surface);
+
+  if (!subsurface->subsurface)
+    goto error_3;
+
+  return subsurface;
+
+ error_3:
+  wl_surface_destroy (subsurface->surface);
+ error_2:
+  free (subsurface);
+ error_1:
+  return NULL;
+}
+
+static struct test_subsurface *
+make_test_subsurface_with_parent (struct test_subsurface *parent)
+{
+  struct test_subsurface *subsurface;
+
+  subsurface = malloc (sizeof *subsurface);
+
+  if (!subsurface)
+    goto error_1;
+
+  subsurface->surface
+    = wl_compositor_create_surface (display->compositor);
+
+  if (!subsurface->surface)
+    goto error_2;
+
+  subsurface->subsurface
+    = wl_subcompositor_get_subsurface (subcompositor,
+				       subsurface->surface,
+				       parent->surface);
+
+  if (!subsurface->subsurface)
+    goto error_3;
+
+  return subsurface;
+
+ error_3:
+  wl_surface_destroy (subsurface->surface);
+ error_2:
+  free (subsurface);
+ error_1:
+  return NULL;
+}
+
+static void
+test_single_step (enum test_kind kind)
+{
+  struct wl_buffer *buffer;
+  struct wl_region *region;
+
+  test_log ("running test step: %s", test_names[kind]);
+
+  switch (kind)
+    {
+    case MAP_WINDOW_KIND:
+      buffer = load_png_image (display, "tiny.png");
+
+      if (!buffer)
+	report_test_failure ("failed to load tiny.png");
+
+      wl_surface_attach (wayland_surface, buffer, 0, 0);
+      wl_surface_damage (wayland_surface, 0, 0, INT_MAX, INT_MAX);
+      submit_surface_opaque_region (wayland_surface, 0, 0, 4, 4);
+      wl_surface_commit (wayland_surface);
+      wl_buffer_destroy (buffer);
+      break;
+
+    case SUBSURFACE_UNDER_KIND:
+      /* Make a subsurface, and then place it *under* the parent.
+	 Wait for a frame callback, damage it, and check the
+	 results.  */
+      subsurfaces[0] = make_test_subsurface ();
+
+      if (!subsurfaces[0])
+	report_test_failure ("failed to create subsurface");
+
+      subsurface_base_png
+	= load_png_image (display, "subsurface_base.png");
+
+      if (!subsurface_base_png)
+	report_test_failure ("failed to load subsurface_base.png");
+
+      subsurface_damage_png
+	= load_png_image (display, "subsurface_damage.png");
+
+      if (!subsurface_damage_png)
+	report_test_failure ("failed to load subsurface_damage.png");
+
+      wl_subsurface_place_below (subsurfaces[0]->subsurface,
+				 wayland_surface);
+      wl_surface_attach (subsurfaces[0]->surface, subsurface_base_png,
+			 0, 0);
+      wl_surface_damage (subsurfaces[0]->surface, 0, 0, 1024, 1024);
+      submit_surface_opaque_region (subsurfaces[0]->surface,
+				    0, 0, 1024, 1024);
+      wl_surface_commit (subsurfaces[0]->surface);
+      wait_frame_callback (wayland_surface);
+      sleep_or_verify ();
+
+      wl_surface_attach (subsurfaces[0]->surface, subsurface_damage_png,
+			 0, 0);
+      wl_surface_damage (subsurfaces[0]->surface, 256, 256, 512, 512);
+      wl_surface_commit (subsurfaces[0]->surface);
+      wait_frame_callback (wayland_surface);
+      sleep_or_verify ();
+
+      test_single_step (SUBSURFACE_OVER_KIND);
+      break;
+
+    case SUBSURFACE_OVER_KIND:
+      /* Make a subsurface, and then place it over the parent.  Set an
+	 opaque region and attach a buffer.  Move the subsurface. */
+      subsurfaces[1] = make_test_subsurface ();
+
+      if (!subsurfaces[1])
+	report_test_failure ("failed to create subsurface");
+
+      subsurface_1_png
+	= load_png_image (display, "subsurface_1.png");
+
+      if (!subsurface_1_png)
+	report_test_failure ("failed to load subsurface_1.png");
+
+      subsurface_1_damaged_png
+	= load_png_image (display, "subsurface_1_damaged.png");
+
+      if (!subsurface_1_damaged_png)
+	report_test_failure ("failed to load subsurface_1_damaged.png");
+
+      /* Now, move the surface a little.  */
+      wl_subsurface_set_position (subsurfaces[1]->subsurface, 40, 40);
+
+      /* Set an opaque region.  */
+      submit_surface_opaque_region (subsurfaces[1]->surface,
+				    0, 0, 256, 256);
+
+      /* Damage the subsurface.  */
+      wl_surface_attach (subsurfaces[1]->surface, subsurface_1_png,
+			 0, 0);
+      wl_surface_damage (subsurfaces[1]->surface, 0, 0, 256, 256);
+
+      /* Commit the subsurface and its parent.  */
+      wl_surface_commit (subsurfaces[1]->surface);
+      wait_frame_callback (wayland_surface);
+      sleep_or_verify ();
+
+      /* Change the opaque region.  */
+      region = wl_compositor_create_region (display->compositor);
+      wl_region_add (region, 0, 0, 256, 256);
+      wl_region_subtract (region, 128, 128, 70, 70);
+      wl_surface_set_opaque_region (subsurfaces[1]->surface, region);
+      wl_region_destroy (region);
+
+      /* Attach a buffer with transparency.  */
+      wl_surface_attach (subsurfaces[1]->surface, subsurface_1_damaged_png,
+			 0, 0);
+      wl_surface_damage (subsurfaces[1]->surface, 128, 128, 70, 70);
+
+      /* Commit the subsurface and its parent.  */
+      wl_surface_commit (subsurfaces[1]->surface);
+      wait_frame_callback (wayland_surface);
+      sleep_or_verify ();
+      test_single_step (SUBSURFACE_MOVE_KIND);
+      break;
+
+    case SUBSURFACE_MOVE_KIND:
+      /* Move the subsurface to the right a little and check that the
+	 correct area is exposed.  */
+      wl_subsurface_set_position (subsurfaces[1]->subsurface, 50, 50);
+      wait_frame_callback (wayland_surface);
+      sleep_or_verify ();
+
+      /* Move the subsurface to the right a little more.  */
+      wl_subsurface_set_position (subsurfaces[1]->subsurface, 100, 100);
+      wait_frame_callback (wayland_surface);
+      sleep_or_verify ();
+      test_single_step (SUBSURFACE_STACKING_KIND);
+      break;
+
+    case SUBSURFACE_STACKING_KIND:
+      /* Stack the first test subsurface above the other test
+	 subsurface.  Then, load a transparent pattern into the first
+	 subsurface to verify the stacking order.  */
+
+      subsurface_transparency_png
+	= load_png_image (display, "subsurface_transparency.png");
+
+      if (!subsurface_transparency_png)
+	report_test_failure ("failed to load subsurface_transparency.png");
+
+      wl_subsurface_place_above (subsurfaces[0]->subsurface,
+				 subsurfaces[1]->surface);
+      wl_surface_attach (subsurfaces[0]->surface,
+			 subsurface_transparency_png, 0, 0);
+
+      /* Also update the opaque region.  */
+      submit_surface_opaque_region (subsurfaces[0]->surface,
+				    640, 640, 128, 128);
+      wl_surface_damage (subsurfaces[0]->surface, 0, 0, 1024, 1024);
+      wl_surface_commit (subsurfaces[0]->surface);
+      wait_frame_callback (wayland_surface);
+      sleep_or_verify ();
+
+      /* Afterwards, damage the other test subsurface and see if the
+	 damage is composited correctly.  */
+      submit_surface_opaque_region (subsurfaces[1]->surface,
+				    0, 0, 256, 256);
+      wl_surface_attach (subsurfaces[1]->surface, subsurface_1_png,
+			 0, 0);
+      wl_surface_damage (subsurfaces[1]->surface, 128, 128, 70, 70);
+
+      /* Commit the subsurface and its parent.  */
+      wl_surface_commit (subsurfaces[1]->surface);
+      wait_frame_callback (wayland_surface);
+      sleep_or_verify ();
+
+      test_single_step (SUBSURFACE_TREE_KIND);
+      break;
+
+    case SUBSURFACE_TREE_KIND:
+      /* Create two subsurfaces attached to the other test subsurface;
+	 1 below, 1 over.  */
+      subsurfaces[2]
+	= make_test_subsurface_with_parent (subsurfaces[1]);
+      subsurfaces[3]
+	= make_test_subsurface_with_parent (subsurfaces[1]);
+
+      if (!subsurfaces[2] || !subsurfaces[3])
+	report_test_failure ("failed to create subsurfaces");
+
+      gradient_png = load_png_image (display, "gradient.png");
+
+      if (!gradient_png)
+	report_test_failure ("failed to load gradient.png");
+
+      cow_transparent_png = load_png_image (display, "cow_transparent.png");
+
+      if (!cow_transparent_png)
+	report_test_failure ("failed to load cow_transparent.png");
+
+      wl_subsurface_place_below (subsurfaces[2]->subsurface,
+				 subsurfaces[1]->surface);
+      wl_subsurface_place_above (subsurfaces[3]->subsurface,
+				 subsurfaces[1]->surface);
+
+      /* Attach buffers to the various subsurfaces and commit
+	 them.  */
+      wl_surface_attach (subsurfaces[2]->surface, gradient_png,
+			 0, 0);
+      wl_surface_attach (subsurfaces[3]->surface, cow_transparent_png,
+			 0, 0);
+      submit_surface_opaque_region (subsurfaces[2]->surface, 0, 0,
+				    100, 300);
+      wl_surface_damage (subsurfaces[2]->surface, 0, 0, INT_MAX, INT_MAX);
+      wl_surface_damage (subsurfaces[3]->surface, 0, 0, INT_MAX, INT_MAX);
+      wl_surface_commit (subsurfaces[2]->surface);
+      wl_surface_commit (subsurfaces[3]->surface);
+
+      /* Nothing should happen to the surface here.  */
+      wait_frame_callback (wayland_surface);
+      sleep_or_verify ();
+
+      /* Nor here.  */
+      wl_surface_commit (subsurfaces[1]->surface);
+
+      /* Until here.  */
+      wait_frame_callback (wayland_surface);
+      sleep_or_verify ();
+
+      /* Now, unmap the surface.  Subsurfaces 2, 3, 4 should all
+	 disappear!  */
+      wl_surface_attach (subsurfaces[1]->surface, NULL, 0, 0);
+      wl_surface_commit (subsurfaces[1]->surface);
+      wl_surface_commit (subsurfaces[1]->surface);
+      wait_frame_callback (wayland_surface);
+      sleep_or_verify ();
+
+      /* Map it again.  All subsurfaces should appear again, this time
+	 with the opaque circle in subsurface 2 transparent.  */
+      wl_surface_attach (subsurfaces[1]->surface, subsurface_1_damaged_png,
+			 0, 0);
+
+      region = wl_compositor_create_region (display->compositor);
+      wl_region_add (region, 0, 0, 256, 256);
+      wl_region_subtract (region, 128, 128, 70, 70);
+      wl_surface_set_opaque_region (subsurfaces[1]->surface, region);
+      wl_region_destroy (region);
+
+      wl_surface_damage (subsurfaces[1]->surface, 128, 128, 70, 70);
+      wl_surface_commit (subsurfaces[1]->surface);
+      wait_frame_callback (wayland_surface);
+      sleep_or_verify ();
+
+      /* Move subsurface 1 to where it gets obscured by the opaque
+	 region of the view above.  Verify that the views all move
+	 accordingly.  */
+      wl_subsurface_set_position (subsurfaces[1]->subsurface, 640, 640);
+      wait_frame_callback (wayland_surface);
+      sleep_or_verify ();
+
+      /* Move one of the views further to the right.  */
+      wl_subsurface_set_position (subsurfaces[2]->subsurface, 100, 100);
+      wl_surface_commit (subsurfaces[1]->surface);
+      wait_frame_callback (wayland_surface);
+      sleep_or_verify ();
+      break;
+    }
+
+  if (kind == LAST_TEST)
+    test_complete ();
+}
+
+
+
+static void
+handle_test_surface_mapped (void *data, struct test_surface *surface,
+			    uint32_t xid, const char *display_string)
+{
+  /* Sleep for 1 second to ensure that the window is exposed and
+     redirected.  */
+  sleep (1);
+
+  /* Start the test.  */
+  test_surface_window = xid;
+
+  /* Run the test again.  */
+  test_single_step (SUBSURFACE_UNDER_KIND);
+}
+
+static const struct test_surface_listener test_surface_listener =
+  {
+    handle_test_surface_mapped,
+  };
+
+
+
+static void
+handle_wl_callback_done (void *data, struct wl_callback *callback,
+			   uint32_t callback_data)
+{
+  bool *flag;
+
+  wl_callback_destroy (callback);
+
+  /* Now tell wait_frame_callback to break out of the loop.  */
+  flag = data;
+  *flag = true;
+}
+
+static const struct wl_callback_listener wl_callback_listener =
+  {
+    handle_wl_callback_done,
+  };
+
+
+
+static void
+wait_frame_callback (struct wl_surface *surface)
+{
+  struct wl_callback *callback;
+  bool flag;
+
+  /* Commit surface and wait for a frame callback.  */
+
+  callback = wl_surface_frame (surface);
+  flag = false;
+
+  wl_callback_add_listener (callback, &wl_callback_listener,
+			    &flag);
+  wl_surface_commit (surface);
+
+  while (!flag)
+    {
+      if (wl_display_dispatch (display->display) == -1)
+        die ("wl_display_dispatch");
+    }
+}
+
+static void
+run_test (void)
+{
+  if (!make_test_surface (display, &wayland_surface,
+			  &test_surface))
+    report_test_failure ("failed to create test surface");
+
+  test_surface_add_listener (test_surface, &test_surface_listener,
+			     NULL);
+  test_single_step (MAP_WINDOW_KIND);
+
+  while (true)
+    {
+      if (wl_display_dispatch (display->display) == -1)
+        die ("wl_display_dispatch");
+    }
+}
+
+int
+main (void)
+{
+  test_init ();
+  display = open_test_display (test_interfaces,
+			       ARRAYELTS (test_interfaces));
+
+  if (!display)
+    report_test_failure ("failed to open display");
+
+  run_test ();
+}
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