Offscreen QPA: implement a native interface

Many code paths simply expect to have a native interface
available, and won't check if a plugin is returning nullptr
for it. This leads to crashes or local workarounds
(e.g. 3197932e6fb03fb9c0ff669af858cb94e3836d79). Instead,
have offscreen implement a dummy native interface.

This requires shuffling some code for the X11 integration.

Pick-to: 5.15
Change-Id: I2bdceee379e4ded9b085ebbb4d03d1e074f60726
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 16 insertions, 8 deletions

diff --git a/src/plugins/platforms/offscreen/qoffscreenintegration_x11.cpp b/src/plugins/platforms/offscreen/qoffscreenintegration_x11.cpp
index bb4d8aeaa1..a11da2d543 100644
--- a/src/plugins/platforms/offscreen/qoffscreenintegration_x11.cpp
+++ b/src/plugins/platforms/offscreen/qoffscreenintegration_x11.cpp
@@ -76,6 +76,8 @@ private:
     QOffscreenX11Connection *m_connection;
 };
 
+QOffscreenX11Integration::~QOffscreenX11Integration() = default;
+
 bool QOffscreenX11Integration::hasCapability(QPlatformIntegration::Capability cap) const
 {
     switch (cap) {
@@ -88,21 +90,27 @@ bool QOffscreenX11Integration::hasCapability(QPlatformIntegration::Capability ca
 
 QPlatformOpenGLContext *QOffscreenX11Integration::createPlatformOpenGLContext(QOpenGLContext *context) const
 {
-    if (!m_connection)
-        m_connection.reset(new QOffscreenX11Connection);
+    auto &connection = nativeInterface()->m_connection;
+
+    if (!connection)
+        connection.reset(new QOffscreenX11Connection);
 
-    if (!m_connection->display())
+    if (!connection->display())
         return nullptr;
 
-    return new QOffscreenX11GLXContext(m_connection->x11Info(), context);
+    return new QOffscreenX11GLXContext(connection->x11Info(), context);
 }
 
-QPlatformNativeInterface *QOffscreenX11Integration::nativeInterface() const
+QOffscreenX11PlatformNativeInterface *QOffscreenX11Integration::nativeInterface() const
 {
-   return const_cast<QOffscreenX11Integration *>(this);
+   if (!m_nativeInterface)
+       m_nativeInterface.reset(new QOffscreenX11PlatformNativeInterface);
+   return static_cast<QOffscreenX11PlatformNativeInterface *>(m_nativeInterface.data());
 }
 
-void *QOffscreenX11Integration::nativeResourceForScreen(const QByteArray &resource, QScreen *screen)
+QOffscreenX11PlatformNativeInterface::~QOffscreenX11PlatformNativeInterface() = default;
+
+void *QOffscreenX11PlatformNativeInterface::nativeResourceForScreen(const QByteArray &resource, QScreen *screen)
 {
     Q_UNUSED(screen);
     if (resource.toLower() == QByteArrayLiteral("display") ) {
@@ -114,7 +122,7 @@ void *QOffscreenX11Integration::nativeResourceForScreen(const QByteArray &resour
 }
 
 #ifndef QT_NO_OPENGL
-void *QOffscreenX11Integration::nativeResourceForContext(const QByteArray &resource, QOpenGLContext *context) {
+void *QOffscreenX11PlatformNativeInterface::nativeResourceForContext(const QByteArray &resource, QOpenGLContext *context) {
     if (resource.toLower() == QByteArrayLiteral("glxconfig") ) {
         if (context) {
             QOffscreenX11GLXContext *glxPlatformContext = static_cast<QOffscreenX11GLXContext *>(context->handle());