Ensure offscreen surface used during cleanup is created on gui thread

Windows uses a QWindow to back QOffscreenSurface so we must needs
create it on the gui thread. To complicate matters we don't know the
format used by Qt 3D until the Renderer is initialized. So we have to
defer creation of the offscreen surface until that time and do it in
the gui thread with the correct format.

Task-number: QTBUG-57496
Change-Id: Idaad23c2229ab069f3e02c8d075be8e6718a8a50
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>

2 files changed, 17 insertions, 0 deletions

diff --git a/src/render/frontend/qrenderaspect.cpp b/src/render/frontend/qrenderaspect.cpp
index 4ba5c208a..14555d15a 100644
--- a/src/render/frontend/qrenderaspect.cpp
+++ b/src/render/frontend/qrenderaspect.cpp
@@ -121,6 +121,7 @@
 #include <Qt3DRender/private/rendersettings_p.h>
 #include <Qt3DRender/private/backendnode_p.h>
 #include <Qt3DRender/private/rendercapture_p.h>
+#include <Qt3DRender/private/offscreensurfacehelper_p.h>
 
 #include <Qt3DCore/qentity.h>
 #include <Qt3DCore/qtransform.h>
@@ -442,6 +443,12 @@ void QRenderAspect::onRegistered()
     d->m_renderer = new Render::Renderer(d->m_renderType);
     d->m_renderer->setNodeManagers(d->m_nodeManagers);
 
+    // Create a helper for deferring creation of an offscreen surface used during cleanup
+    // to the main thread, after we knwo what the surface format in use is.
+    d->m_offscreenHelper = new Render::OffscreenSurfaceHelper(d->m_renderer);
+    d->m_offscreenHelper->moveToThread(QCoreApplication::instance()->thread());
+    d->m_renderer->setOffscreenSurfaceHelper(d->m_offscreenHelper);
+
     // Register backend types now that we have a renderer
     d->registerBackendTypes();
 
@@ -479,6 +486,11 @@ void QRenderAspect::onUnregistered()
     // Waits for the render thread to join (if using threaded renderer)
     delete d->m_renderer;
     d->m_renderer = nullptr;
+
+    // Queue the offscreen surface helper for deletion on the main thread.
+    // That will take care of deleting the offscreen surface itself.
+    d->m_offscreenHelper->deleteLater();
+    d->m_offscreenHelper = nullptr;
 }
 
 QVector<Qt3DCore::QAspectJobPtr> QRenderAspectPrivate::createGeometryRendererJobs()
diff --git a/src/render/frontend/qrenderaspect_p.h b/src/render/frontend/qrenderaspect_p.h
index f196c2ec2..d2c789ada 100644
--- a/src/render/frontend/qrenderaspect_p.h
+++ b/src/render/frontend/qrenderaspect_p.h
@@ -67,6 +67,10 @@ class AbstractRenderer;
 class NodeManagers;
 }
 
+namespace Render {
+class OffscreenSurfaceHelper;
+}
+
 class QT3DRENDERSHARED_PRIVATE_EXPORT QRenderAspectPrivate : public Qt3DCore::QAbstractAspectPrivate
 {
 public:
@@ -89,6 +93,7 @@ public:
     bool m_initialized;
     QList<QSceneIOHandler *> m_sceneIOHandler;
     QRenderAspect::RenderType m_renderType;
+    Render::OffscreenSurfaceHelper *m_offscreenHelper;
 };
 
 }