Don't render when scene is not changing

Reduce CPU and GPU load by checking if the scene has changed and render
only if it has.

Task-number: QT3DS-4042
Change-Id: I54e447760f04fdad8d64319f326245175b471331
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>
Reviewed-by: Tomi Korpipää <tomi.korpipaa@qt.io>

3 files changed, 9 insertions, 5 deletions

diff --git a/src/engine/Qt3DSRenderRuntimeBinding.cpp b/src/engine/Qt3DSRenderRuntimeBinding.cpp
index 28c5403..e830e0f 100644
--- a/src/engine/Qt3DSRenderRuntimeBinding.cpp
+++ b/src/engine/Qt3DSRenderRuntimeBinding.cpp
@@ -1505,9 +1505,11 @@ struct Qt3DSRenderSceneManager : public Q3DStudio::ISceneManager,
                                        bool firstFrame) override
     {
         Qt3DSRenderScene *theFirstScene = nullptr;
-        for (QT3DSU32 idx = 0, end = m_Scenes.size(); idx < end && theFirstScene == nullptr; ++idx)
+        for (QT3DSU32 idx = 0, end = m_Scenes.size(); idx < end; ++idx) {
             if (m_Scenes[idx].second->m_RuntimePresentation == inPresentation)
                 theFirstScene = m_Scenes[idx].second;
+            m_Scenes[idx].second->TransferDirtyProperties();
+        }
 
         if (theFirstScene && theFirstScene->m_Presentation) {
             m_LastRenderedScene = theFirstScene;
diff --git a/src/engine/Qt3DSRuntimeView.cpp b/src/engine/Qt3DSRuntimeView.cpp
index fd3be65..2335cf1 100644
--- a/src/engine/Qt3DSRuntimeView.cpp
+++ b/src/engine/Qt3DSRuntimeView.cpp
@@ -179,7 +179,7 @@ public:
     void Cleanup() override;
 
     bool CanRender() override;
-    void Render() override;
+    bool Render() override;
     bool WasLastFrameDirty() override;
 
     bool HandleMessage(const QEvent *inEvent) override;
@@ -394,8 +394,9 @@ bool CRuntimeView::CanRender()
  *  returns KD_TRUE to call egl_render and swap properly, KD_FALSE if there has been no scene update
  *or redraw.
  */
-void CRuntimeView::Render()
+bool CRuntimeView::Render()
 {
+    bool ret = true;
     if (m_Application.mPtr == nullptr) {
         // InitializeGraphics has not been called
         QT3DS_ASSERT(false);
@@ -403,7 +404,7 @@ void CRuntimeView::Render()
 
     PerfLogGeneralEvent1(DATALOGGER_FRAME);
 
-    m_Application->UpdateAndRender();
+    ret = m_Application->UpdateAndRender();
 
     if (m_startupTime < 0 && m_startupTimer && m_startupTimer->isValid()) {
 
@@ -457,6 +458,7 @@ void CRuntimeView::Render()
 
         manager.PopState();
     }
+    return ret;
 }
 
 bool CRuntimeView::WasLastFrameDirty()
diff --git a/src/engine/Qt3DSRuntimeView.h b/src/engine/Qt3DSRuntimeView.h
index e3f57d1..e0061b0 100644
--- a/src/engine/Qt3DSRuntimeView.h
+++ b/src/engine/Qt3DSRuntimeView.h
@@ -185,7 +185,7 @@ public: // loading
 
     virtual bool CanRender() = 0;
 
-    virtual void Render() = 0;
+    virtual bool Render() = 0;
 
     virtual bool WasLastFrameDirty() = 0;