visionOS: Add support for immersive spaces

The QNativeInterface::QVisionOSApplication interface allows opening
and dismissing an immersive space, as well as registering a compositor
layer implementation that can be used to configure the compositor
layer and render to it with Metal.

The compositor layer implementation is consulted both for immersive
spaces triggered explicitly, and when the default scene of the app
is set to CPSceneSessionRoleImmersiveSpaceApplication via the
UIApplicationPreferredDefaultSceneSessionRole in the Info.plist.

All of this requires that the application follows the SwiftUI app
lifecyle, so our application entrypoint is now a SwiftUI app. The
existing qt_main_wrapper used for the QIOSEventDispatcher handles
this transparently, so there is no change for the user, who will
still receive a callback to main() when the Swift app is ready
to build its UI hierarchy.

Change-Id: Ic295010d714e90cd4d3f66bd90f321438659f3a6
Reviewed-by: Christian Strømme <christian.stromme@qt.io>

4 files changed, 64 insertions, 0 deletions

diff --git a/src/gui/CMakeLists.txt b/src/gui/CMakeLists.txt
index cef71318d8..75f55bbc42 100644
--- a/src/gui/CMakeLists.txt
+++ b/src/gui/CMakeLists.txt
@@ -376,6 +376,11 @@ qt_internal_extend_target(Gui CONDITION MACOS
         ${FWAppKit}
 )
 
+qt_internal_extend_target(Gui CONDITION UIKIT
+    SOURCES
+        platform/ios/qiosnativeinterface.cpp
+)
+
 qt_internal_extend_target(Gui CONDITION WASM
     SOURCES
         platform/wasm/qwasmnativeinterface.cpp
diff --git a/src/gui/kernel/qguiapplication.cpp b/src/gui/kernel/qguiapplication.cpp
index f2b914f203..5228ac9477 100644
--- a/src/gui/kernel/qguiapplication.cpp
+++ b/src/gui/kernel/qguiapplication.cpp
@@ -4401,6 +4401,9 @@ void *QGuiApplication::resolveInterface(const char *name, int revision) const
 #if QT_CONFIG(wayland)
     QT_NATIVE_INTERFACE_RETURN_IF(QWaylandApplication, platformNativeInterface());
 #endif
+#if defined(Q_OS_VISIONOS)
+    QT_NATIVE_INTERFACE_RETURN_IF(QVisionOSApplication, platformIntegration);
+#endif
 
     return QCoreApplication::resolveInterface(name, revision);
 }
diff --git a/src/gui/kernel/qguiapplication_platform.h b/src/gui/kernel/qguiapplication_platform.h
index 545bf75c84..d9ff01bf14 100644
--- a/src/gui/kernel/qguiapplication_platform.h
+++ b/src/gui/kernel/qguiapplication_platform.h
@@ -32,6 +32,22 @@ struct wl_pointer;
 struct wl_touch;
 #endif
 
+#if defined(Q_OS_VISIONOS) || defined(Q_QDOC)
+#  ifdef __OBJC__
+Q_FORWARD_DECLARE_OBJC_CLASS(CP_OBJECT_cp_layer_renderer_capabilities);
+typedef CP_OBJECT_cp_layer_renderer_capabilities *cp_layer_renderer_capabilities_t;
+Q_FORWARD_DECLARE_OBJC_CLASS(CP_OBJECT_cp_layer_renderer_configuration);
+typedef CP_OBJECT_cp_layer_renderer_configuration *cp_layer_renderer_configuration_t;
+Q_FORWARD_DECLARE_OBJC_CLASS(CP_OBJECT_cp_layer_renderer);
+typedef CP_OBJECT_cp_layer_renderer *cp_layer_renderer_t;
+#  else
+typedef struct cp_layer_renderer_capabilities_s *cp_layer_renderer_capabilities_t;
+typedef struct cp_layer_renderer_configuration_s *cp_layer_renderer_configuration_t;
+typedef struct cp_layer_renderer_s *cp_layer_renderer_t;
+#  endif
+#endif
+
+
 QT_BEGIN_NAMESPACE
 
 namespace QNativeInterface
@@ -61,6 +77,20 @@ struct Q_GUI_EXPORT QWaylandApplication
 };
 #endif
 
+#if defined(Q_OS_VISIONOS) || defined(Q_QDOC)
+struct Q_GUI_EXPORT QVisionOSApplication
+{
+    QT_DECLARE_NATIVE_INTERFACE(QVisionOSApplication, 1, QGuiApplication)
+    struct ImmersiveSpaceCompositorLayer {
+        virtual void configure(cp_layer_renderer_capabilities_t, cp_layer_renderer_configuration_t) const {}
+        virtual void render(cp_layer_renderer_t) = 0;
+    };
+    virtual void setImmersiveSpaceCompositorLayer(ImmersiveSpaceCompositorLayer *layer) = 0;
+    virtual void openImmersiveSpace() = 0;
+    virtual void dismissImmersiveSpace() = 0;
+};
+#endif
+
 } // QNativeInterface
 
 QT_END_NAMESPACE
diff --git a/src/gui/platform/ios/qiosnativeinterface.cpp b/src/gui/platform/ios/qiosnativeinterface.cpp
new file mode 100644
index 0000000000..c942709e33
--- /dev/null
+++ b/src/gui/platform/ios/qiosnativeinterface.cpp
@@ -0,0 +1,26 @@
+// Copyright (C) 2024 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#include <QtGui/private/qguiapplication_p.h>
+
+QT_BEGIN_NAMESPACE
+
+using namespace QNativeInterface::Private;
+
+#if defined(Q_OS_VISIONOS)
+
+/*!
+    \class QNativeInterface::QVisionOSApplication
+    \since 6.8
+    \internal
+    \preliminary
+    \brief Native interface to QGuiApplication, to be retrieved from QPlatformIntegration.
+    \inmodule QtGui
+    \ingroup native-interfaces
+*/
+
+QT_DEFINE_NATIVE_INTERFACE(QVisionOSApplication);
+
+#endif // Q_OS_VISIONOS
+
+QT_END_NAMESPACE