xwayland: Set xrandr primary output

To find XWayland output that should be the primary one, iterate through all
XWayland outputs, and compare their geometry to the geometry of the primary
logical monitor.

To avoid possible race conditions (Mutter's monitor configuration already
updated, but Xrandr not yet), set the output both after Randr notifications and
after 'monitors-changed' signal.

https://gitlab.gnome.org/GNOME/mutter/-/issues/1407

Signed-off-by: Aleksandr Mezin <mezin.alexander@gmail.com>
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1558>

src/wayland/meta-wayland-private.h

@@ -67,6 +67,10 @@ typedef struct
   GList *x11_windows;
 
   MetaXWaylandDnd *dnd;
+
+  gboolean has_xrandr;
+  int rr_event_base;
+  int rr_error_base;
 } MetaXWaylandManager;
 
 struct _MetaWaylandCompositor

src/wayland/meta-xwayland-private.h

@@ -36,6 +36,9 @@ meta_xwayland_complete_init (MetaDisplay *display,
 void
 meta_xwayland_shutdown (MetaXWaylandManager *manager);
 
+gboolean
+meta_xwayland_handle_xevent (XEvent *event);
+
 /* wl_data_device/X11 selection interoperation */
 void     meta_xwayland_init_dnd         (Display *xdisplay);
 void     meta_xwayland_shutdown_dnd     (Display *xdisplay);

src/wayland/meta-xwayland.c

@@ -39,8 +39,10 @@
 #include <linux/random.h>
 #endif
 #include <unistd.h>
+#include <X11/extensions/Xrandr.h>
 #include <X11/Xauth.h>
 
+#include "backends/meta-monitor-manager-private.h"
 #include "backends/meta-settings-private.h"
 #include "core/main-private.h"
 #include "meta/main.h"
@@ -52,6 +54,9 @@ static int display_number_override = -1;
 
 static void meta_xwayland_stop_xserver (MetaXWaylandManager *manager);
 
+static void
+meta_xwayland_set_primary_output (Display *xdisplay);
+
 void
 meta_xwayland_associate_window_with_surface (MetaWindow          *window,
                                              MetaWaylandSurface  *surface)
@@ -871,17 +876,50 @@ meta_xwayland_init (MetaXWaylandManager  *manager,
   return TRUE;
 }
 
+static void
+monitors_changed_cb (MetaMonitorManager *monitor_manager)
+{
+  MetaX11Display *x11_display = meta_get_display ()->x11_display;
+
+  meta_xwayland_set_primary_output (x11_display->xdisplay);
+}
+
 static void
 on_x11_display_closing (MetaDisplay *display)
 {
   Display *xdisplay = meta_x11_display_get_xdisplay (display->x11_display);
 
   meta_xwayland_shutdown_dnd (xdisplay);
+  g_signal_handlers_disconnect_by_func (meta_monitor_manager_get (),
+                                        monitors_changed_cb,
+                                        NULL);
   g_signal_handlers_disconnect_by_func (display,
                                         on_x11_display_closing,
                                         NULL);
 }
 
+static void
+meta_xwayland_init_xrandr (MetaXWaylandManager *manager,
+                           Display             *xdisplay)
+{
+  MetaMonitorManager *monitor_manager = meta_monitor_manager_get ();
+
+  manager->has_xrandr = XRRQueryExtension (xdisplay,
+                                           &manager->rr_event_base,
+                                           &manager->rr_error_base);
+
+  if (!manager->has_xrandr)
+    return;
+
+  XRRSelectInput (xdisplay, DefaultRootWindow (xdisplay),
+                  RRCrtcChangeNotifyMask | RROutputChangeNotifyMask);
+
+  g_signal_connect (monitor_manager, "monitors-changed",
+                    G_CALLBACK (monitors_changed_cb), NULL);
+
+  meta_xwayland_set_primary_output (xdisplay);
+}
+
 /* To be called right after connecting */
 void
 meta_xwayland_complete_init (MetaDisplay *display,
@@ -904,6 +942,7 @@ meta_xwayland_complete_init (MetaDisplay *display,
                     G_CALLBACK (on_x11_display_closing), NULL);
   meta_xwayland_init_dnd (xdisplay);
   add_local_user_to_xhost (xdisplay);
+  meta_xwayland_init_xrandr (manager, xdisplay);
 
   if (meta_get_x11_display_policy () == META_DISPLAY_POLICY_ON_DEMAND)
     {
@@ -945,3 +984,79 @@ meta_xwayland_shutdown (MetaXWaylandManager *manager)
       g_clear_pointer (&manager->auth_file, g_free);
     }
 }
+
+static void
+meta_xwayland_set_primary_output (Display *xdisplay)
+{
+  XRRScreenResources *resources;
+  MetaMonitorManager *monitor_manager;
+  MetaLogicalMonitor *primary_monitor;
+  int i;
+
+  monitor_manager = meta_monitor_manager_get ();
+  primary_monitor =
+    meta_monitor_manager_get_primary_logical_monitor (monitor_manager);
+
+  if (!primary_monitor)
+    return;
+
+  resources = XRRGetScreenResourcesCurrent (xdisplay,
+                                            DefaultRootWindow (xdisplay));
+  if (!resources)
+    return;
+
+  for (i = 0; i < resources->noutput; i++)
+    {
+      RROutput output_id = resources->outputs[i];
+      XRROutputInfo *xrandr_output;
+      XRRCrtcInfo *crtc_info = NULL;
+      MetaRectangle crtc_geometry;
+
+      xrandr_output = XRRGetOutputInfo (xdisplay, resources, output_id);
+      if (!xrandr_output)
+        continue;
+
+      if (xrandr_output->crtc)
+        crtc_info = XRRGetCrtcInfo (xdisplay, resources, xrandr_output->crtc);
+
+      XRRFreeOutputInfo (xrandr_output);
+
+      if (!crtc_info)
+        continue;
+
+      crtc_geometry.x = crtc_info->x;
+      crtc_geometry.y = crtc_info->y;
+      crtc_geometry.width = crtc_info->width;
+      crtc_geometry.height = crtc_info->height;
+
+      XRRFreeCrtcInfo (crtc_info);
+
+      if (meta_rectangle_equal (&crtc_geometry, &primary_monitor->rect))
+        {
+          XRRSetOutputPrimary (xdisplay, DefaultRootWindow (xdisplay),
+                               output_id);
+          break;
+        }
+    }
+
+  XRRFreeScreenResources (resources);
+}
+
+gboolean
+meta_xwayland_handle_xevent (XEvent *event)
+{
+  MetaWaylandCompositor *compositor = meta_wayland_compositor_get_default ();
+  MetaXWaylandManager *manager = &compositor->xwayland_manager;
+
+  if (meta_xwayland_dnd_handle_event (event))
+    return TRUE;
+
+  if (manager->has_xrandr && event->type == manager->rr_event_base + RRNotify)
+    {
+      MetaX11Display *x11_display = meta_get_display ()->x11_display;
+      meta_xwayland_set_primary_output (x11_display->xdisplay);
+      return TRUE;
+    }
+
+  return FALSE;
+}

src/x11/events.c

@@ -1793,7 +1793,7 @@ meta_x11_display_handle_xevent (MetaX11Display *x11_display,
 
 #ifdef HAVE_WAYLAND
   if (meta_is_wayland_compositor () &&
-      meta_xwayland_dnd_handle_event (event))
+      meta_xwayland_handle_xevent (event))
     {
       bypass_gtk = bypass_compositor = TRUE;
       goto out;