xwayland: Notify of root size change with XRandR emulation

Some clients (typically Java, but maybe others) rely on ConfigureNotify
or RRScreenChangeNotify events to tell that the XRandR request is
successful.

When emulated XRandR is used in Xwayland, compute the emulated root size
and send the expected ConfigureNotify and RRScreenChangeNotify events
with the emulated size of the root window to the asking X11 client.

Note that the root window size does not actually change, as XRandR
emulation is achieved by scaling the client window using viewports in
Wayland, so this event is sort of misleading.

Also, because Xwayland is using viewports, emulating XRandR does not
reconfigure the outputs location, meaning that the actual size of the
root window which encompasses all the outputs together may not change
in a multi-monitor setup. To work around this limitation, when using an
emulated mode, we report the size of that emulated mode alone as the
root size for the configure notify event.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>

hw/xwayland/xwayland-output.c

@@ -468,6 +468,85 @@ xwl_output_set_randr_emu_props(struct xwl_screen *xwl_screen, ClientPtr client)
                               xwl_output_set_randr_emu_prop_callback, &prop);
 }
 
+static inline void
+xwl_output_get_emulated_root_size(struct xwl_output *xwl_output,
+                                  ClientPtr client,
+                                  int *width,
+                                  int *height)
+{
+    struct xwl_screen *xwl_screen = xwl_output->xwl_screen;
+    struct xwl_emulated_mode *emulated_mode;
+
+    emulated_mode = xwl_output_get_emulated_mode_for_client(xwl_output, client);
+    /* If not an emulated mode, just return the actual screen size */
+    if (!emulated_mode) {
+        *width = xwl_screen->width;
+        *height = xwl_screen->height;
+        return;
+    }
+
+    if (xwl_output->rotation & (RR_Rotate_0 | RR_Rotate_180)) {
+        *width = emulated_mode->width;
+        *height = emulated_mode->height;
+    } else {
+        *width = emulated_mode->height;
+        *height = emulated_mode->width;
+    }
+}
+
+static int
+xwl_output_get_rr_event_mask(WindowPtr pWin, ClientPtr client)
+{
+    RREventPtr pRREvent, *pHead;
+
+    dixLookupResourceByType((void **) &pHead, pWin->drawable.id,
+                            RREventType, client, DixReadAccess);
+
+    pRREvent = NULL;
+    if (pHead) {
+        for (pRREvent = *pHead; pRREvent; pRREvent = pRREvent->next)
+            if (pRREvent->client == client)
+                break;
+        }
+
+    if (pRREvent)
+        return pRREvent->mask;
+
+    return 0;
+}
+
+static void
+xwl_output_notify_emulated_root_size(struct xwl_output *xwl_output,
+                                     ClientPtr client,
+                                     int new_emulated_root_width,
+                                     int new_emulated_root_height)
+{
+    struct xwl_screen *xwl_screen = xwl_output->xwl_screen;
+    ScreenPtr pScreen = xwl_screen->screen;
+    WindowPtr pRoot = pScreen->root;
+    xEvent event = {
+             .u.configureNotify.event = pRoot->drawable.id,
+             .u.configureNotify.window = pRoot->drawable.id,
+             .u.configureNotify.aboveSibling = None,
+             .u.configureNotify.x = 0,
+             .u.configureNotify.y = 0,
+             .u.configureNotify.width = new_emulated_root_width,
+             .u.configureNotify.height = new_emulated_root_height,
+             .u.configureNotify.borderWidth = pRoot->borderWidth,
+             .u.configureNotify.override = pRoot->overrideRedirect
+         };
+     event.u.u.type = ConfigureNotify;
+
+     if (!client || client == serverClient || client->clientGone)
+         return;
+
+     if (EventMaskForClient(pRoot, client) & StructureNotifyMask)
+         WriteEventsToClient(client, 1, &event);
+
+     if (xwl_output_get_rr_event_mask(pRoot, client) & RRScreenChangeNotifyMask)
+         RRDeliverScreenEvent(client, pRoot, pScreen);
+}
+
 void
 xwl_output_set_window_randr_emu_props(struct xwl_screen *xwl_screen,
                                       WindowPtr window)
@@ -482,10 +561,16 @@ void
 xwl_output_set_emulated_mode(struct xwl_output *xwl_output, ClientPtr client,
                              RRModePtr mode, Bool from_vidmode)
 {
+    int old_emulated_width, old_emulated_height;
+    int new_emulated_width, new_emulated_height;
+
     DebugF("XWAYLAND: xwl_output_set_emulated_mode from %s: %dx%d\n",
            from_vidmode ? "vidmode" : "randr",
            mode->mode.width, mode->mode.height);
 
+    xwl_output_get_emulated_root_size(xwl_output, client,
+                                      &old_emulated_width, &old_emulated_height);
+
     /* modes[0] is the actual (not-emulated) output mode */
     if (mode == xwl_output->randr_output->modes[0])
         xwl_output_remove_emulated_mode_for_client(xwl_output, client);
@@ -495,6 +580,15 @@ xwl_output_set_emulated_mode(struct xwl_output *xwl_output, ClientPtr client,
     xwl_screen_check_resolution_change_emulation(xwl_output->xwl_screen);
 
     xwl_output_set_randr_emu_props(xwl_output->xwl_screen, client);
+
+    xwl_output_get_emulated_root_size(xwl_output, client,
+                                      &new_emulated_width, &new_emulated_height);
+
+    if (new_emulated_width != old_emulated_width ||
+        new_emulated_height != old_emulated_height)
+        xwl_output_notify_emulated_root_size(xwl_output, client,
+                                             new_emulated_width,
+                                             new_emulated_height);
 }
 
 static void