Manage X11 display and harden surface recovery

Reuse and store the X11 Display pointer (as void*) so createSurface
doesn't repeatedly open displays. Close the display during cleanup and
before device recreation.

Add a short 200ms delay in recreateDevice to let the GPU driver
stabilize, and explicitly recheck surface support and query surface
capabilities before recreating the swapchain.

src/vulkanwidget.cpp

@@ -8,6 +8,7 @@
 #include <QCloseEvent>
 #include <QWindow>
 #include <QApplication>
+#include <QThread>
 #include <algorithm>
 #include <cmath>
 
@@ -35,6 +36,7 @@ VulkanWidget::VulkanWidget(QWidget *parent)
     , m_surface(VK_NULL_HANDLE)
     , m_swapchain(VK_NULL_HANDLE)
     , m_commandPool(VK_NULL_HANDLE)
+    , m_x11Display(nullptr)
     , m_initialized(false)
     , m_renderingEnabled(false)
     , m_needsResize(false)
@@ -342,12 +344,22 @@ bool VulkanWidget::createSurface()
 #elif defined(__linux__)
     VkXlibSurfaceCreateInfoKHR createInfo = {};
     createInfo.sType = VK_STRUCTURE_TYPE_XLIB_SURFACE_CREATE_INFO_KHR;
-    // Get X11 display - use default display
+    
-    createInfo.dpy = XOpenDisplay(nullptr);
+    // Reuse existing X11 display or open a new one
-    if (!createInfo.dpy) {
+    Display* x11Display = static_cast<Display*>(m_x11Display);
-        qDebug() << "Failed to open X11 display";
+    if (!x11Display) {
-        return false;
+        x11Display = XOpenDisplay(nullptr);
+        if (!x11Display) {
+            qDebug() << "Failed to open X11 display";
+            return false;
+        }
+        m_x11Display = x11Display;
+        qDebug() << "X11 display opened and stored";
+    } else {
+        qDebug() << "Reusing existing X11 display";
     }
+    
+    createInfo.dpy = x11Display;
     createInfo.window = static_cast<Window>(window->winId());
 
     VkResult result = vkCreateXlibSurfaceKHR(m_instance, &createInfo, nullptr, &m_surface);
@@ -1072,6 +1084,15 @@ void VulkanWidget::cleanupVulkan()
         vkDestroySurfaceKHR(m_instance, m_surface, nullptr);
     }
     
+    // Close X11 display if it was opened (Linux only)
+#ifdef __linux__
+    if (m_x11Display) {
+        XCloseDisplay(static_cast<Display*>(m_x11Display));
+        m_x11Display = nullptr;
+        qDebug() << "X11 display closed";
+    }
+#endif
+
     // Cleanup instance
     if (m_instance != VK_NULL_HANDLE) {
         vkDestroyInstance(m_instance, nullptr);
@@ -1303,7 +1324,22 @@ bool VulkanWidget::recreateDevice()
         qDebug() << "Surface destroyed";
     }
     
+    // Close and reset X11 display (Linux only) - will be reopened when creating new surface
+#ifdef __linux__
+    if (m_x11Display) {
+        XCloseDisplay(static_cast<Display*>(m_x11Display));
+        m_x11Display = nullptr;
+        qDebug() << "X11 display closed for recreation";
+    }
+#endif
+    
     // Now recreate everything from surface onwards
+    
+    // Important: Add a small delay to let the GPU driver fully reset
+    // This prevents VK_ERROR_SURFACE_LOST_KHR on some systems
+    qDebug() << "Waiting for GPU driver to stabilize...";
+    QThread::msleep(200); // 200ms delay
+    
     // Step 1: Recreate surface
     if (!createSurface()) {
         setError("Failed to recreate surface after device lost");
@@ -1311,6 +1347,16 @@ bool VulkanWidget::recreateDevice()
     }
     qDebug() << "Surface recreated";
     
+    // Verify the physical device still supports this surface
+    VkBool32 surfaceSupported = VK_FALSE;
+    vkGetPhysicalDeviceSurfaceSupportKHR(m_physicalDevice, m_queueFamilyIndex, m_surface, &surfaceSupported);
+    if (!surfaceSupported) {
+        qDebug() << "Physical device no longer supports the surface after recovery";
+        setError("Surface not supported by physical device after recovery");
+        return false;
+    }
+    qDebug() << "Surface support verified";
+    
     // Step 2: Recreate logical device
     if (!createDevice()) {
         setError("Failed to recreate device after device lost");
@@ -1319,6 +1365,16 @@ bool VulkanWidget::recreateDevice()
     qDebug() << "Logical device recreated";
     
     // Step 3: Recreate swapchain
+    // Query surface capabilities again to ensure they're current
+    VkSurfaceCapabilitiesKHR surfaceCaps;
+    VkResult capsResult = vkGetPhysicalDeviceSurfaceCapabilitiesKHR(m_physicalDevice, m_surface, &surfaceCaps);
+    if (capsResult != VK_SUCCESS) {
+        qDebug() << "Failed to query surface capabilities, error:" << capsResult;
+        setError("Failed to query surface capabilities after device lost");
+        return false;
+    }
+    qDebug() << "Surface capabilities validated";
+    
     if (!createSwapchain()) {
         setError("Failed to recreate swapchain after device lost");
         return false;

src/vulkanwidget.h

@@ -214,6 +214,7 @@ private:
     VkSurfaceKHR m_surface;
     VkSwapchainKHR m_swapchain;
     VkCommandPool m_commandPool;
+    void* m_x11Display; // X11 Display pointer (Linux only), stored as void* to avoid X11 header dependency
     std::vector<VkCommandBuffer> m_commandBuffers;
     std::vector<VkSemaphore> m_imageAvailableSemaphores;
     std::vector<VkSemaphore> m_renderFinishedSemaphores;