tr2/shell: center offscreen window on game launch

docs/tr2/CHANGELOG.md

@@ -15,6 +15,7 @@
 - added the current music track and timestamp to the savegame so they now persist on load (#2579)
 - added waterfalls to the savegame so that they now persist on load (#2686)
 - added support for aspect ratio-specific images (#1840)
+- added a guard to ensure the game always starts on a visible screen even after unplugging displays (#2819)
 - changed savegame files to be stored in the `saves` directory (#2087)
 - changed the default fog distance to 22 tiles cutting off at 30 tiles to match TR1X (#1622)
 - changed the number of static mesh slots from 50 to 256 (#2734)

src/tr2/game/shell/common.c

@@ -138,10 +138,35 @@ static void M_SyncToWindow(void)
             width = 1280;
             height = 720;
         }
-        if (x == -1 && y == -1) { // default config state
+
-            const SHELL_SIZE display_size = Shell_GetCurrentDisplaySize();
+        // Handle default position
-            x = (display_size.w - width) / 2;
+        if (x == -1 && y == -1) {
-            y = (display_size.h - height) / 2;
+            SDL_DisplayMode display_mode;
+            SDL_GetCurrentDisplayMode(0, &display_mode);
+            x = (display_mode.w - width) / 2;
+            y = (display_mode.h - height) / 2;
+        } else {
+            // Adjust window position if completely offscreen
+            bool on_screen = false;
+            const int32_t num_displays = SDL_GetNumVideoDisplays();
+            for (int32_t i = 0; i < num_displays; i++) {
+                SDL_Rect bounds;
+                SDL_GetDisplayBounds(i, &bounds);
+                if (x + width > bounds.x && x < bounds.x + bounds.w
+                    && y + height > bounds.y && y < bounds.y + bounds.h) {
+                    on_screen = true;
+                    break;
+                }
+            }
+            if (!on_screen) {
+                x = 0;
+                y = 0;
+                // Find the first display to reposition the window
+                SDL_Rect bounds;
+                SDL_GetDisplayBounds(0, &bounds);
+                x = bounds.x + (bounds.w - width) / 2;
+                y = bounds.y + (bounds.h - height) / 2;
+            }
         }
 
         SDL_SetWindowFullscreen(g_SDLWindow, 0);