[client] displayserver: add new earlyInit to the interface

Some platforms such as Wayland need to set environment vairables before
SDL is initialized, as such this change detects the display server
before SDL has started and calls the new `earlyInit` method providing
the implementation an opportunity to set things up.

client/displayservers/SDL/sdl.c

@@ -33,6 +33,11 @@ struct SDLDSState
 
 static struct SDLDSState sdl;
 
+static bool sdlEarlyInit(void)
+{
+  return true;
+}
+
 static void sdlInit(SDL_SysWMinfo * info)
 {
   memset(&sdl, 0, sizeof(sdl));
@@ -143,6 +148,7 @@ static void sdlWarpMouse(int x, int y, bool exiting)
 struct LG_DisplayServerOps LGDS_SDL =
 {
   .subsystem      = SDL_SYSWM_UNKNOWN,
+  .earlyInit      = sdlEarlyInit,
   .init           = sdlInit,
   .startup        = sdlStartup,
   .shutdown       = sdlShutdown,

client/include/interface/displayserver.h

@@ -49,7 +49,10 @@ struct LG_DisplayServerOps
 {
   const SDL_SYSWM_TYPE subsystem;
 
-  /* early initialization */
+  /* called before SDL has been initialized */
+  bool (*earlyInit)(void);
+
+  /* called after SDL has been initialized */
   void (*init)(SDL_SysWMinfo * info);
 
   /* called at startup after window creation, renderer and/or SPICE is ready */

client/src/main.c

@@ -1654,20 +1654,49 @@ static int lg_run(void)
        if (g_cursor.sens < -9) g_cursor.sens = -9;
   else if (g_cursor.sens >  9) g_cursor.sens =  9;
 
-  if (getenv("WAYLAND_DISPLAY"))
+
+  // try to early detect the platform
+  SDL_SYSWM_TYPE subsystem = SDL_SYSWM_UNKNOWN;
+       if (getenv("WAYLAND_DISPLAY")) subsystem = SDL_SYSWM_WAYLAND;
+  else if (getenv("DISPLAY"        )) subsystem = SDL_SYSWM_X11;
+  else
+    DEBUG_WARN("Unknown subsystem, falling back to SDL default");
+
+  // search for the best displayserver ops to use
+  for(int i = 0; i < LG_DISPLAYSERVER_COUNT; ++i)
+    if (LG_DisplayServers[i]->subsystem == subsystem)
     {
-     DEBUG_INFO("Wayland detected");
+      g_state.ds = LG_DisplayServers[i];
-     if (getenv("SDL_VIDEODRIVER") == NULL)
+      break;
+    }
+
+  assert(g_state.ds);
+
+  // set any null methods to the fallback
+#define SET_FALLBACK(x) \
+  if (!g_state.ds->x) g_state.ds->x = LG_DisplayServers[0]->x;
+  SET_FALLBACK(earlyInit);
+  SET_FALLBACK(getProp);
+  SET_FALLBACK(init);
+  SET_FALLBACK(startup);
+  SET_FALLBACK(shutdown);
+  SET_FALLBACK(free);
+  SET_FALLBACK(eventFilter);
+  SET_FALLBACK(grabPointer);
+  SET_FALLBACK(ungrabKeyboard);
+  SET_FALLBACK(warpMouse);
+  SET_FALLBACK(cbInit);
+  SET_FALLBACK(cbNotice);
+  SET_FALLBACK(cbRelease);
+  SET_FALLBACK(cbRequest);
+#undef SET_FALLBACK
+
+  // init the subsystem
+  if (!g_state.ds->earlyInit())
   {
-       int err = setenv("SDL_VIDEODRIVER", "wayland", 1);
+    DEBUG_ERROR("Subsystem early init failed");
-       if (err < 0)
-       {
-         DEBUG_ERROR("Unable to set the env variable SDL_VIDEODRIVER: %d", err);
     return -1;
   }
-       DEBUG_INFO("SDL_VIDEODRIVER has been set to wayland");
-     }
-  }
 
   if (!params.noScreensaver)
     SDL_SetHint(SDL_HINT_VIDEO_ALLOW_SCREENSAVER, "1");
@@ -1793,36 +1822,6 @@ static int lg_run(void)
     return -1;
   }
 
-  // search for the best displayserver ops to use
-  for(int i = 0; i < LG_DISPLAYSERVER_COUNT; ++i)
-    if (LG_DisplayServers[i]->subsystem == g_state.wminfo.subsystem)
-    {
-      g_state.ds = LG_DisplayServers[i];
-      break;
-    }
-
-  if (!g_state.ds)
-    g_state.ds = LG_DisplayServers[0];
-
-  // set any null methods to the fallback
-#define SET_FALLBACK(x) \
-  if (!g_state.ds->x) g_state.ds->x = LG_DisplayServers[0]->x;
-  SET_FALLBACK(getProp);
-  SET_FALLBACK(init);
-  SET_FALLBACK(startup);
-  SET_FALLBACK(shutdown);
-  SET_FALLBACK(free);
-  SET_FALLBACK(eventFilter);
-  SET_FALLBACK(grabPointer);
-  SET_FALLBACK(ungrabKeyboard);
-  SET_FALLBACK(warpMouse);
-  SET_FALLBACK(cbInit);
-  SET_FALLBACK(cbNotice);
-  SET_FALLBACK(cbRelease);
-  SET_FALLBACK(cbRequest);
-#undef SET_FALLBACK
-
-  // init the subsystem
   g_state.ds->init(&g_state.wminfo);
 
   SDL_SetHint(SDL_HINT_VIDEO_MINIMIZE_ON_FOCUS_LOSS,