Render enough frames to flush the Qt3D pipeline when dirty

Sometimes Qt3D needs 2 frames if it involves introspecting and then
compiling shaders. So render at least this many frames when needed.

The change in formatting is pushed upon us by the clang-format use
in the pre-commit hook.

Change-Id: Ie9f48876351a8d1a7bd0df705a9e43831753ac69
Reviewed-by: Mike Krus <mike.krus@kdab.com>
(cherry picked from commit c2f6cfd0e4c382045a3391dd20809d9bd3b04311)
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>

2 files changed, 19 insertions, 11 deletions

diff --git a/src/quick3d/imports/scene3d/scene3ditem.cpp b/src/quick3d/imports/scene3d/scene3ditem.cpp
index c8c0e0f59..1c610d8bc 100644
--- a/src/quick3d/imports/scene3d/scene3ditem.cpp
+++ b/src/quick3d/imports/scene3d/scene3ditem.cpp
@@ -219,6 +219,7 @@ Scene3DItem::Scene3DItem(QQuickItem *parent)
     , m_cameraAspectRatioMode(AutomaticAspectRatio)
     , m_compositingMode(FBO)
     , m_dummySurface(nullptr)
+    , m_framesToRender(ms_framesNeededToFlushPipeline)
 {
     setFlag(QQuickItem::ItemHasContents, true);
     setAcceptedMouseButtons(Qt::MouseButtonMask);
@@ -542,8 +543,13 @@ bool Scene3DItem::needsRender(QRenderAspect *renderAspect)
             || (renderAspectPriv
                 && renderAspectPriv->m_renderer
                 && renderAspectPriv->m_renderer->shouldRender());
-    m_dirty = false;
-    return dirty;
+
+    if (m_dirty) {
+        --m_framesToRender;
+        if (m_framesToRender <= 0)
+            m_dirty = false;
+    }
+    return dirty || m_framesToRender > 0;
 }
 
 // This function is triggered in the context of the Main Thread
@@ -911,15 +917,14 @@ QSGNode *Scene3DItem::updatePaintNode(QSGNode *node, QQuickItem::UpdatePaintNode
         updateWindowSurface();
         managerNode->init();
         // Note: ChangeArbiter is only set after aspect was registered
-
-        // This allows Scene3DItem to know when it needs to re-render as a result of frontend nodes receiving a change.
-        QObject::connect(renderAspectPriv->m_aspectManager->changeArbiter(), &Qt3DCore::QChangeArbiter::receivedChange,
-                         this, [this] { m_dirty = true; }, Qt::DirectConnection);
-
-        // This allows Scene3DItem to know when it needs to re-render as a result of backend nodes receiving a change.
-        // For e.g. nodes being created/destroyed.
-        QObject::connect(renderAspectPriv->m_aspectManager->changeArbiter(), &Qt3DCore::QChangeArbiter::syncedChanges,
-                         this, [this] { m_dirty = true; }, Qt::QueuedConnection);
+        QObject::connect(
+                renderAspectPriv->m_aspectManager->changeArbiter(),
+                &Qt3DCore::QChangeArbiter::receivedChange, this,
+                [this] {
+                    m_dirty = true;
+                    m_framesToRender = ms_framesNeededToFlushPipeline;
+                },
+                Qt::DirectConnection);
     }
 
     const bool usesFBO = m_compositingMode == FBO;
diff --git a/src/quick3d/imports/scene3d/scene3ditem_p.h b/src/quick3d/imports/scene3d/scene3ditem_p.h
index 7680ee8b1..827f6c29d 100644
--- a/src/quick3d/imports/scene3d/scene3ditem_p.h
+++ b/src/quick3d/imports/scene3d/scene3ditem_p.h
@@ -169,6 +169,9 @@ private:
     QOffscreenSurface *m_dummySurface;
     QVector<Scene3DView *> m_views;
     QMetaObject::Connection m_windowConnection;
+    qint8 m_framesToRender;
+
+    static const qint8 ms_framesNeededToFlushPipeline = 2;
 };
 
 } // Qt3DRender