backend: Introduce helpers for turning from/to clutter/evdev buttons

We have multiple implementations of these types of transformations, and
one is broken. Instead of just fixing it, add this helper so that it can
use it instead.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3325>

src/backends/meta-backend-private.h

@@ -209,3 +209,9 @@ void meta_backend_update_from_event (MetaBackend  *backend,
 
 char * meta_backend_get_vendor_name (MetaBackend *backend,
                                      const char  *pnp_id);
+
+META_EXPORT_TEST
+uint32_t meta_clutter_button_to_evdev (uint32_t clutter_button);
+
+META_EXPORT_TEST
+uint32_t meta_evdev_button_to_clutter (uint32_t evdev_button);

src/backends/meta-backend.c

@@ -119,6 +119,12 @@ static guint signals[N_SIGNALS];
 
 #define HIDDEN_POINTER_TIMEOUT 300 /* ms */
 
+#ifndef BTN_LEFT
+#define BTN_LEFT 0x110
+#define BTN_RIGHT 0x111
+#define BTN_MIDDLE 0x112
+#endif
+
 struct _MetaBackendPrivate
 {
   MetaContext *context;
@@ -1797,3 +1803,37 @@ meta_backend_get_vendor_name (MetaBackend *backend,
   return g_strdup (pnp_id);
 #endif
 }
+
+uint32_t
+meta_clutter_button_to_evdev (uint32_t clutter_button)
+{
+  switch (clutter_button)
+    {
+    case CLUTTER_BUTTON_PRIMARY:
+      return BTN_LEFT;
+    case CLUTTER_BUTTON_SECONDARY:
+      return BTN_RIGHT;
+    case CLUTTER_BUTTON_MIDDLE:
+      return BTN_MIDDLE;
+    }
+
+  return (clutter_button + (BTN_LEFT - 1)) - 4;
+}
+
+uint32_t
+meta_evdev_button_to_clutter (uint32_t evdev_button)
+{
+  switch (evdev_button)
+    {
+    case BTN_LEFT:
+      return CLUTTER_BUTTON_PRIMARY;
+    case BTN_RIGHT:
+      return CLUTTER_BUTTON_SECONDARY;
+    case BTN_MIDDLE:
+      return CLUTTER_BUTTON_MIDDLE;
+    }
+
+  g_return_val_if_fail (evdev_button > BTN_LEFT, 0);
+
+  return (evdev_button - (BTN_LEFT - 1)) + 4;
+}

src/tests/button-transform-tests.c

@@ -0,0 +1,118 @@
+/*
+ * Copyright (C) 2023 Red Hat Inc.
+ *
+ * This program 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 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program 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 this program; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "config.h"
+
+#include "button-transform-tests.h"
+
+#include <linux/input-event-codes.h>
+
+#include "backends/meta-backend-private.h"
+
+static void
+meta_test_clutter_to_evdev (void)
+{
+  struct {
+    uint32_t clutter_button;
+    uint32_t evdev_button;
+  } test_cases[] = {
+    { .clutter_button = CLUTTER_BUTTON_PRIMARY, .evdev_button = BTN_LEFT },
+    { .clutter_button = CLUTTER_BUTTON_MIDDLE, .evdev_button = BTN_MIDDLE },
+    { .clutter_button = CLUTTER_BUTTON_SECONDARY, .evdev_button = BTN_RIGHT },
+  };
+  size_t i;
+
+  for (i = 0; i < G_N_ELEMENTS (test_cases); i++)
+    {
+      uint32_t clutter_button;
+      uint32_t expected_evdev_button;
+      uint32_t evdev_button;
+
+      clutter_button = test_cases[i].clutter_button;
+      expected_evdev_button = test_cases[i].evdev_button;
+
+      evdev_button = meta_clutter_button_to_evdev (clutter_button);
+      g_assert_cmpuint (evdev_button, ==, expected_evdev_button);
+    }
+}
+
+static void
+meta_test_evdev_to_clutter (void)
+{
+  struct {
+    uint32_t evdev_button;
+    uint32_t clutter_button;
+  } test_cases[] = {
+    { .evdev_button = BTN_LEFT, .clutter_button = CLUTTER_BUTTON_PRIMARY },
+    { .evdev_button = BTN_MIDDLE, .clutter_button = CLUTTER_BUTTON_MIDDLE },
+    { .evdev_button = BTN_RIGHT, .clutter_button = CLUTTER_BUTTON_SECONDARY },
+  };
+  size_t i;
+
+  for (i = 0; i < G_N_ELEMENTS (test_cases); i++)
+    {
+      uint32_t evdev_button;
+      uint32_t expected_clutter_button;
+      uint32_t clutter_button;
+
+      evdev_button = test_cases[i].evdev_button;
+      expected_clutter_button = test_cases[i].clutter_button;
+
+      clutter_button = meta_evdev_button_to_clutter (evdev_button);
+      g_assert_cmpuint (clutter_button, ==, expected_clutter_button);
+    }
+}
+
+static void
+meta_test_evdev_to_clutter_to_evdev (void)
+{
+  uint32_t test_cases[] = {
+    BTN_LEFT,
+    BTN_MIDDLE,
+    BTN_RIGHT,
+    BTN_SIDE,
+    BTN_BACK,
+    BTN_FORWARD,
+  };
+  size_t i;
+
+  for (i = 0; i < G_N_ELEMENTS (test_cases); i++)
+    {
+      uint32_t evdev_button;
+      uint32_t expected_evdev_button;
+      uint32_t clutter_button;
+
+      evdev_button = test_cases[i];
+      expected_evdev_button = evdev_button;
+
+      clutter_button = meta_evdev_button_to_clutter (evdev_button);
+      evdev_button = meta_clutter_button_to_evdev (clutter_button);
+      g_assert_cmpuint (evdev_button, ==, expected_evdev_button);
+    }
+}
+
+void
+init_button_transform_tests (void)
+{
+  g_test_add_func ("/backends/button-transform/clutter-to-evdev",
+                   meta_test_clutter_to_evdev);
+  g_test_add_func ("/backends/button-transform/evdev-clutter",
+                   meta_test_evdev_to_clutter);
+  g_test_add_func ("/backends/button-transform/evdev-clutter-evdev",
+                   meta_test_evdev_to_clutter_to_evdev);
+}

src/tests/button-transform-tests.h

@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2023 Red Hat Inc.
+ *
+ * This program 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 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program 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 this program; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#pragma once
+
+void init_button_transform_tests (void);

src/tests/meson.build

@@ -242,6 +242,7 @@ test_cases += [
       'monitor-transform-tests.h',
       'orientation-manager-unit-tests.c',
       'hdr-metadata-unit-tests.c',
+      'button-transform-tests.c',
     ],
     'depends': [
       test_client,

src/tests/unit-tests.c

@@ -39,6 +39,7 @@
 #include "tests/meta-test-utils.h"
 #include "tests/orientation-manager-unit-tests.h"
 #include "tests/hdr-metadata-unit-tests.h"
+#include "tests/button-transform-tests.h"
 
 MetaContext *test_context;
 
@@ -244,6 +245,7 @@ init_tests (void)
   init_monitor_transform_tests ();
   init_orientation_manager_tests ();
   init_hdr_metadata_tests ();
+  init_button_transform_tests ();
 }
 
 int