Improve error handling in C++ Skia Renderer API

- Don't try to create a GLX context when we only have an XCB window handle,
  XLib is required for that.
- Make it possible to create a NativeWindowHandle from Xlib data types.

Fixes #2978

api/cpp/include/slint_platform.h

@@ -255,13 +255,22 @@ public:
     }
 
 #    if !defined(__APPLE__) && !defined(_WIN32) && !defined(_WIN64)
-    static NativeWindowHandle from_x11(uint32_t /*xcb_window_t*/ window,
-                                       uint32_t /*xcb_visualid_t*/ visual_id,
-                                       xcb_connection_t *connection, int screen)
+    static NativeWindowHandle from_x11_xcb(uint32_t /*xcb_window_t*/ window,
+                                           uint32_t /*xcb_visualid_t*/ visual_id,
+                                           xcb_connection_t *connection, int screen)
     {
 
-        return { cbindgen_private::slint_new_raw_window_handle_x11(window, visual_id, connection,
-                                                                   screen) };
+        return { cbindgen_private::slint_new_raw_window_handle_x11_xcb(window, visual_id,
+                                                                       connection, screen) };
+    }
+
+    static NativeWindowHandle from_x11_xlib(uint32_t /*Window*/ window,
+                                            unsigned long /*VisualID*/ visual_id,
+                                            void /*Display*/ *display, int screen)
+    {
+
+        return { cbindgen_private::slint_new_raw_window_handle_x11_xlib(window, visual_id, display,
+                                                                        screen) };
     }
 
     static NativeWindowHandle from_wayland(wl_surface *surface, wl_display *display)

api/cpp/platform.rs

@@ -249,7 +249,7 @@ pub mod skia {
     }
 
     #[no_mangle]
-    pub unsafe extern "C" fn slint_new_raw_window_handle_x11(
+    pub unsafe extern "C" fn slint_new_raw_window_handle_x11_xcb(
         window: u32,
         visual_id: u32,
         connection: *mut c_void,
@@ -263,6 +263,21 @@ pub mod skia {
         Box::into_raw(Box::new(handle)) as CppRawHandleOpaque
     }
 
+    #[no_mangle]
+    pub unsafe extern "C" fn slint_new_raw_window_handle_x11_xlib(
+        window: core::ffi::c_ulong,
+        visual_id: core::ffi::c_ulong,
+        display: *mut c_void,
+        screen: core::ffi::c_int,
+    ) -> CppRawHandleOpaque {
+        use raw_window_handle::{XlibDisplayHandle, XlibWindowHandle};
+        let handle = CppRawHandle(
+            RawWindowHandle::Xlib(init_raw!(XlibWindowHandle { window, visual_id })),
+            RawDisplayHandle::Xlib(init_raw!(XlibDisplayHandle { display, screen })),
+        );
+        Box::into_raw(Box::new(handle)) as CppRawHandleOpaque
+    }
+
     #[no_mangle]
     pub unsafe extern "C" fn slint_new_raw_window_handle_wayland(
         surface: *mut c_void,

api/cpp/tests/manual/platform_qt/main.cpp

@@ -45,7 +45,7 @@ static slint_platform::NativeWindowHandle window_handle_for_qt_window(QWindow *w
             native->nativeResourceForWindow(QByteArray("connection"), window));
     auto screen = quintptr(native->nativeResourceForWindow(QByteArray("screen"), window));
 
-    return slint_platform::NativeWindowHandle::from_x11(wid, wid, connection, screen);
+    return slint_platform::NativeWindowHandle::from_x11_xcb(wid, wid, connection, screen);
 #endif
 }
 
@@ -56,6 +56,7 @@ class MyWindow : public QWindow, public slint_platform::WindowAdapter
 public:
     MyWindow(QWindow *parentWindow = nullptr) : QWindow(parentWindow)
     {
+        resize(640, 480);
         m_renderer.emplace(window_handle_for_qt_window(this), physical_size());
     }