Fix loading screen graphical artifacts on window resize

Recreate Vulkan swapchain in LoadingScreen::render() when the dirty flag
is set, so resizing the window during world loading no longer renders
into a stale swapchain with mismatched framebuffers.

include/rendering/loading_screen.hpp

@@ -4,6 +4,8 @@
 #include <string>
 #include <vector>
 
+struct SDL_Window;
+
 namespace wowee {
 namespace rendering {
 
@@ -27,11 +29,13 @@ public:
 
     // Must be set before initialize() for Vulkan texture upload
     void setVkContext(VkContext* ctx) { vkCtx = ctx; }
+    void setSDLWindow(SDL_Window* win) { sdlWindow = win; }
 
 private:
     bool loadImage(const std::string& path);
 
     VkContext* vkCtx = nullptr;
+    SDL_Window* sdlWindow = nullptr;
 
     // Vulkan texture for background image
     VkImage bgImage = VK_NULL_HANDLE;

src/core/application.cpp

@@ -3065,6 +3065,7 @@ void Application::loadOnlineWorldTerrain(uint32_t mapId, float x, float y, float
     // --- Loading screen for online mode ---
     rendering::LoadingScreen loadingScreen;
     loadingScreen.setVkContext(window->getVkContext());
+    loadingScreen.setSDLWindow(window->getSDLWindow());
     bool loadingScreenOk = loadingScreen.initialize();
 
     auto showProgress = [&](const char* msg, float progress) {

src/rendering/loading_screen.cpp

@@ -5,6 +5,7 @@
 #include <imgui_internal.h>
 #include <imgui_impl_vulkan.h>
 #include <imgui_impl_sdl2.h>
+#include <SDL2/SDL.h>
 #include <random>
 #include <chrono>
 #include <cstdio>
@@ -327,6 +328,15 @@ void LoadingScreen::render() {
 
     // Submit the frame to Vulkan (loading screen runs outside the main render loop)
     if (vkCtx) {
+        // Handle window resize: recreate swapchain before acquiring an image
+        if (vkCtx->isSwapchainDirty() && sdlWindow) {
+            int w = 0, h = 0;
+            SDL_GetWindowSize(sdlWindow, &w, &h);
+            if (w > 0 && h > 0) {
+                vkCtx->recreateSwapchain(w, h);
+            }
+        }
+
         uint32_t imageIndex = 0;
         VkCommandBuffer cmd = vkCtx->beginFrame(imageIndex);
         if (cmd != VK_NULL_HANDLE) {