Fix Alt+Enter client crash

docs/CHANGELOG.md

@@ -52,6 +52,7 @@ Version 1.3.0 (Bakeapple): Not yet released
 - Optimize network performance for `af_obj_update` packets and bot decommission logic
 - Sync animation state for crouched players in first person spectate view
 - Sync rail scanner in first person spectate
+- Fix Alt+Enter crash in Direct3D 11 renderer
 
 Version 1.2.2 (Willow): Released Jan-04-2026
 --------------------------------

game_patch/graphics/d3d11/gr_d3d11.cpp

@@ -220,6 +220,14 @@ namespace df::gr::d3d11
                 dxgi_factory->CreateSwapChain(device_, &sd, &swap_chain_)
             );
         }
+
+        // Alpine uses DXGI's flip presentation model, which requires ResizeBuffers
+        // after mode transitions
+        // Disable DXGI's built-in Alt+Enter fullscreen toggle. DXGI's auto-handling
+        // calls SetFullscreenState internally without the app's knowledge, which causes
+        // the next Present() call to return DXGI_ERROR_INVALID_CALL and crash. We handle
+        // Alt+Enter ourselves via WM_SYSKEYDOWN in the message handler.
+        dxgi_factory->MakeWindowAssociation(hwnd, DXGI_MWA_NO_ALT_ENTER);
     }
 
     void Renderer::init_back_buffer()

game_patch/graphics/d3d11/gr_d3d11_hooks.cpp

@@ -20,8 +20,13 @@ namespace df::gr::d3d11
 {
     static std::optional<Renderer> renderer;
 
+    void update_window_mode();
+
     void msg_handler(UINT msg, WPARAM w_param, LPARAM l_param)
     {
+        if (!renderer) {
+            return;
+        }
         switch (msg) {
         case WM_ACTIVATEAPP:
             if (w_param) {
@@ -32,6 +37,20 @@ namespace df::gr::d3d11
                 xlog::trace("inactive {:x} {:x}", w_param, l_param);
                 renderer->window_inactive();
             }
+            break;
+        case WM_SYSKEYDOWN:
+            // Handle Alt+Enter to toggle between fullscreen and windowed mode.
+            // DXGI's built-in Alt+Enter handling is disabled (MakeWindowAssociation with
+            // DXGI_MWA_NO_ALT_ENTER) to prevent it from calling SetFullscreenState internally,
+            // which would put the swap chain in an inconsistent state and crash on the next Present().
+            if (w_param == VK_RETURN) {
+                auto new_mode = (rf::gr::screen.window_mode == rf::gr::FULLSCREEN)
+                    ? rf::gr::WINDOWED
+                    : rf::gr::FULLSCREEN;
+                rf::gr::screen.window_mode = new_mode;
+                update_window_mode();
+            }
+            break;
         }
     }