backends: Use helper to translate from/to clutter/evdev button codes

This fixes an issue in the MetaEisClient implementation which didn't
offset correctly.

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

src/backends/meta-eis-client.c

@@ -555,22 +555,7 @@ handle_button (MetaEisClient    *client,
   gboolean is_press = eis_event_button_get_is_press (event);
 
   button = eis_event_button_get_button (event);
-  switch (button)
+  button = meta_evdev_button_to_clutter (button);
-    {
-    case 0x110: /* BTN_LEFT */
-      button = CLUTTER_BUTTON_PRIMARY;
-      break;
-    case 0x111: /* BTN_RIGHT */
-      button = CLUTTER_BUTTON_SECONDARY;
-      break;
-    case 0x112: /* BTN_MIDDLE */
-      button = CLUTTER_BUTTON_MIDDLE;
-      break;
-    default:
-      if (button > 0x110)
-        button -= 0x110;
-      break;
-    }
 
   if (button > MAX_BUTTON)
     return;

src/backends/meta-remote-desktop-session.c

@@ -755,27 +755,6 @@ handle_notify_keyboard_keysym (MetaDBusRemoteDesktopSession *skeleton,
   return TRUE;
 }
 
-/* Translation taken from the clutter evdev backend. */
-static int
-translate_to_clutter_button (int button)
-{
-  switch (button)
-    {
-    case BTN_LEFT:
-      return CLUTTER_BUTTON_PRIMARY;
-    case BTN_RIGHT:
-      return CLUTTER_BUTTON_SECONDARY;
-    case BTN_MIDDLE:
-      return CLUTTER_BUTTON_MIDDLE;
-    default:
-      /*
-       * For compatibility reasons, all additional buttons go after the old
-       * 4-7 scroll ones.
-       */
-      return button - (BTN_LEFT - 1) + 4;
-    }
-}
-
 static gboolean
 handle_notify_pointer_button (MetaDBusRemoteDesktopSession *skeleton,
                               GDBusMethodInvocation        *invocation,
@@ -789,7 +768,7 @@ handle_notify_pointer_button (MetaDBusRemoteDesktopSession *skeleton,
   if (!meta_remote_desktop_session_check_can_notify (session, invocation))
     return TRUE;
 
-  button = translate_to_clutter_button (button_code);
+  button = meta_evdev_button_to_clutter (button_code);
 
   if (pressed)
     {

src/backends/native/meta-input-settings-native.c

@@ -376,26 +376,7 @@ meta_input_settings_native_set_scroll_button (MetaInputSettings  *settings,
     }
   else
     {
-      switch (button)
+      evcode = meta_clutter_button_to_evdev (button);
-        {
-        case 1:
-          evcode = BTN_LEFT;
-          break;
-        case 2:
-          evcode = BTN_MIDDLE;
-          break;
-        case 3:
-          evcode = BTN_RIGHT;
-          break;
-        default:
-          /* Compensate for X11 scroll buttons */
-          if (button > 7)
-            button -= 4;
-
-          /* Button is 1-indexed */
-          evcode = (BTN_LEFT - 1) + button;
-        }
-
       method = LIBINPUT_CONFIG_SCROLL_ON_BUTTON_DOWN;
     }
 

src/backends/native/meta-seat-impl.c

@@ -739,7 +739,7 @@ meta_seat_impl_notify_button_in_impl (MetaSeatImpl       *seat_impl,
       if (clutter_input_device_get_device_type (input_device) == CLUTTER_TABLET_DEVICE)
         button_nr = button - BTN_TOOL_PEN + 4;
       else
-        button_nr = button - (BTN_LEFT - 1) + 4;
+        button_nr = meta_evdev_button_to_clutter (button);
       break;
     }
 

src/backends/native/meta-virtual-input-device-native.c

@@ -22,6 +22,7 @@
 #include <glib-object.h>
 #include <linux/input.h>
 
+#include "backends/meta-backend-private.h"
 #include "backends/native/meta-input-thread.h"
 #include "backends/native/meta-seat-native.h"
 #include "backends/native/meta-virtual-input-device-native.h"
@@ -300,26 +301,6 @@ meta_virtual_input_device_native_notify_absolute_motion (ClutterVirtualInputDevi
   g_object_unref (task);
 }
 
-static int
-translate_to_evdev_button (int 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;
-    default:
-      /*
-       * For compatibility reasons, all additional buttons go after the old
-       * 4-7 scroll ones.
-       */
-      return clutter_button + (BTN_LEFT - 1) - 4;
-    }
-}
-
 static gboolean
 notify_button_in_impl (GTask *task)
 {
@@ -333,7 +314,7 @@ notify_button_in_impl (GTask *task)
   if (event->time_us == CLUTTER_CURRENT_TIME)
     event->time_us = g_get_monotonic_time ();
 
-  evdev_button = translate_to_evdev_button (event->button);
+  evdev_button = meta_clutter_button_to_evdev (event->button);
 
   if (get_button_type (evdev_button) != EVDEV_BUTTON_TYPE_BUTTON)
     {