[vulkan linux] Fix native_platform_handle with gtk

Use gtk connection as handle and use it when creating surface.

src/xenia/ui/vulkan/vulkan_context.cc

@@ -73,10 +73,6 @@ bool VulkanContext::Initialize() {
 #ifdef GDK_WINDOWING_X11
     GtkWidget* window_handle =
         static_cast<GtkWidget*>(target_window_->native_handle());
-    GdkDisplay* gdk_display = gtk_widget_get_display(window_handle);
-    assert(GDK_IS_X11_DISPLAY(gdk_display));
-    xcb_connection_t* connection =
-        XGetXCBConnection(gdk_x11_display_get_xdisplay(gdk_display));
     xcb_window_t window =
         gdk_x11_window_get_xid(gtk_widget_get_window(window_handle));
     VkXcbSurfaceCreateInfoKHR create_info;

src/xenia/ui/window_gtk.cc

@@ -9,6 +9,8 @@
 
 #include <string>
 
+#include <X11/Xlib-xcb.h>
+
 #include "xenia/base/assert.h"
 #include "xenia/base/logging.h"
 #include "xenia/base/platform_linux.h"
@@ -81,6 +83,10 @@ void GTKWindow::Create() {
                    NULL);
   g_signal_connect(G_OBJECT(window_), "event", G_CALLBACK(gtk_event_handler_),
                    reinterpret_cast<gpointer>(this));
+
+  GdkDisplay* gdk_display = gtk_widget_get_display(window_);
+  assert(GDK_IS_X11_DISPLAY(gdk_display));
+  connection_ = XGetXCBConnection(gdk_x11_display_get_xdisplay(gdk_display));
 }
 
 bool GTKWindow::OnCreate() {

src/xenia/ui/window_gtk.h

@@ -15,6 +15,7 @@
 
 #include <gdk/gdkx.h>
 #include <gtk/gtk.h>
+#include <xcb/xcb.h>
 
 #include "xenia/base/platform_linux.h"
 #include "xenia/ui/menu_item.h"
@@ -31,7 +32,7 @@ class GTKWindow : public Window {
   ~GTKWindow() override;
 
   NativePlatformHandle native_platform_handle() const override {
-    return nullptr;
+    return connection_;
   }
   NativeWindowHandle native_handle() const override { return window_; }
 
@@ -74,6 +75,7 @@ class GTKWindow : public Window {
  private:
   void Create();
   GtkWidget* window_;
+  xcb_connection_t* connection_;
 
   friend void gtk_event_handler_(GtkWidget*, GdkEvent*, gpointer);
   bool HandleMouse(GdkEventAny* event);