[client] wayland: gracefully degrade when protocols are unsupported

zwp_relative_pointer_manager_v1 and zwp_pointer_constraints_v1 are
supported by GNOME/KDE/sway (and most other compositors), but they are
not a required part of the protocol.

Some users also run software in one-off nested compositors like cage[0]
for an extra layer of isolation; cage, at least, does not support
pointer captures.

This commit makes Looking Glass warn when an optional protocol is
unsupported, and fail if a required one is missing. Pointer grab paths
have a new guard against the aforementioned protocols being missing.

[0]: https://github.com/Hjdskes/cage

client/displayservers/SDL/sdl.c

@@ -38,9 +38,10 @@ static bool sdlEarlyInit(void)
   return true;
 }
 
-static void sdlInit(SDL_SysWMinfo * info)
+static bool sdlInit(SDL_SysWMinfo * info)
 {
   memset(&sdl, 0, sizeof(sdl));
+  return true;
 }
 
 static void sdlStartup(void)

client/displayservers/Wayland/wayland.c

@@ -84,8 +84,6 @@ struct WCBState
 static struct WaylandDSState wm;
 static struct WCBState       wcb;
 
-// Wayland support.
-
 // Registry-handling listeners.
 
 static void registryGlobalHandler(void * data, struct wl_registry * registry,
@@ -279,7 +277,7 @@ static bool waylandEarlyInit(void)
   return true;
 }
 
-static void waylandInit(SDL_SysWMinfo * info)
+static bool waylandInit(SDL_SysWMinfo * info)
 {
   memset(&wm, 0, sizeof(wm));
 
@@ -290,11 +288,29 @@ static void waylandInit(SDL_SysWMinfo * info)
   wl_registry_add_listener(wm.registry, &registryListener, NULL);
   wl_display_roundtrip(wm.display);
 
+  if (!wm.seat || !wm.dataDeviceManager)
+  {
+    DEBUG_ERROR("Compositor missing a required interface, will not proceed");
+    return false;
+  }
+
+  if (!wm.relativePointerManager)
+    DEBUG_WARN("zwp_relative_pointer_manager_v1 not exported by compositor, "
+               "mouse will not be captured");
+  if (!wm.pointerConstraints)
+    DEBUG_WARN("zwp_pointer_constraints_v1 not exported by compositor, mouse "
+               "will not be captured");
+  if (!wm.keyboardInhibitManager)
+    DEBUG_WARN("zwp_keyboard_shortcuts_inhibit_manager_v1 not exported by "
+               "compositor, keyboard will not be grabbed");
+
   wl_seat_add_listener(wm.seat, &seatListener, NULL);
   wl_display_roundtrip(wm.display);
 
   wm.dataDevice = wl_data_device_manager_get_data_device(
       wm.dataDeviceManager, wm.seat);
+
+  return true;
 }
 
 static void waylandStartup(void)
@@ -317,6 +333,9 @@ static const struct zwp_relative_pointer_v1_listener relativePointerListener = {
 
 static void waylandGrabPointer(void)
 {
+  if (!wm.relativePointerManager || !wm.pointerConstraints)
+    return;
+
   if (!wm.relativePointer)
   {
     wm.relativePointer =
@@ -402,8 +421,6 @@ static bool waylandEventFilter(SDL_Event * event)
   return false;
 }
 
-//asdasd
-
 static const char * textMimetypes[] =
 {
   "text/plain",

client/displayservers/X11/x11.c

@@ -81,7 +81,7 @@ static void x11CBSelectionIncr(const XPropertyEvent e);
 static void x11CBSelectionNotify(const XSelectionEvent e);
 static void x11CBXFixesSelectionNotify(const XFixesSelectionNotifyEvent e);
 
-static void x11Init(SDL_SysWMinfo * info)
+static bool x11Init(SDL_SysWMinfo * info)
 {
   memset(&x11, 0, sizeof(x11));
   x11.display = info->info.x11.display;
@@ -110,6 +110,8 @@ static void x11Init(SDL_SysWMinfo * info)
     (unsigned char *)&value,
     1
   );
+
+  return true;
 }
 
 static void x11Startup(void)

client/include/interface/displayserver.h

@@ -65,7 +65,7 @@ struct LG_DisplayServerOps
   bool (*earlyInit)(void);
 
   /* called after SDL has been initialized */
-  void (*init)(SDL_SysWMinfo * info);
+  bool (*init)(SDL_SysWMinfo * info);
 
   /* called at startup after window creation, renderer and/or SPICE is ready */
   void (*startup)();