Engine: get desktop size and modes of display window is on (if able)

Engine/platform/base/sys_main.cpp

@@ -73,9 +73,19 @@ void sys_set_background_mode(bool /*on*/) {
 // ----------------------------------------------------------------------------
 const int DEFAULT_DISPLAY_INDEX = 0; // TODO: is this always right?
 
+// Gets the display index on which the window is currently positioned.
+// Returns default display index in case window does not exist yet, or on any error.
+int sys_get_window_display_index() {
+    int index = -1;
+    SDL_Window *window = sys_get_window();
+    if (window)
+        index = SDL_GetWindowDisplayIndex(window);
+    return index >= 0 ? index : DEFAULT_DISPLAY_INDEX;
+}
+
 int sys_get_desktop_resolution(int &width, int &height) {
     SDL_Rect r;
-    if (SDL_GetDisplayBounds(DEFAULT_DISPLAY_INDEX, &r) != 0) {
+    if (SDL_GetDisplayBounds(sys_get_window_display_index(), &r) != 0) {
         Debug::Printf(kDbgMsg_Error, "SDL_GetDisplayBounds failed: %s", SDL_GetError());
         return -1;
     }
@@ -86,7 +96,7 @@ int sys_get_desktop_resolution(int &width, int &height) {
 
 void sys_get_desktop_modes(std::vector<AGS::Engine::DisplayMode> &dms, int color_depth) {
     SDL_DisplayMode mode;
-    const int display_id = DEFAULT_DISPLAY_INDEX;
+    const int display_id = sys_get_window_display_index();
     const int count = SDL_GetNumDisplayModes(display_id);
     dms.clear();
     for (int i = 0; i < count; ++i) {