Add API to temporarily disable updates in 3D map scene

This is useful for debugging 3D views, to pause scene updates and
inspect some parts of the scene in detail.

python/3d/auto_generated/qgs3dmapscene.sip.in

@@ -112,6 +112,24 @@ Returns the scene's elevation range
 Returns the 3D map settings.
 
 .. versionadded:: 3.30
+%End
+
+    bool hasSceneUpdatesEnabled() const;
+%Docstring
+Returns whether updates of the 3D scene's entities are allowed.
+Normally, scene updates are enabled. But for debugging purposes,
+it may be useful to temporarily disable scene updates.
+
+.. versionadded:: 3.40
+%End
+
+    void setSceneUpdatesEnabled( bool enabled );
+%Docstring
+Sets whether updates of the 3D scene's entities are allowed.
+Normally, scene updates are enabled. But for debugging purposes,
+it may be useful to temporarily disable scene updates.
+
+.. versionadded:: 3.40
 %End
 
  static QMap< QString, Qgs3DMapScene * > openScenes() /Deprecated/;

python/PyQt6/3d/auto_generated/qgs3dmapscene.sip.in

@@ -112,6 +112,24 @@ Returns the scene's elevation range
 Returns the 3D map settings.
 
 .. versionadded:: 3.30
+%End
+
+    bool hasSceneUpdatesEnabled() const;
+%Docstring
+Returns whether updates of the 3D scene's entities are allowed.
+Normally, scene updates are enabled. But for debugging purposes,
+it may be useful to temporarily disable scene updates.
+
+.. versionadded:: 3.40
+%End
+
+    void setSceneUpdatesEnabled( bool enabled );
+%Docstring
+Sets whether updates of the 3D scene's entities are allowed.
+Normally, scene updates are enabled. But for debugging purposes,
+it may be useful to temporarily disable scene updates.
+
+.. versionadded:: 3.40
 %End
 
  static QMap< QString, Qgs3DMapScene * > openScenes() /Deprecated/;

src/3d/qgs3dmapscene.cpp

@@ -322,6 +322,12 @@ void Qgs3DMapScene::onCameraChanged()
 
 void Qgs3DMapScene::updateScene( bool forceUpdate )
 {
+  if ( !mSceneUpdatesEnabled )
+  {
+    QgsDebugMsgLevel( "Scene update skipped", 2 );
+    return;
+  }
+
   if ( forceUpdate )
     QgsEventTracing::addEvent( QgsEventTracing::Instant, QStringLiteral( "3D" ), QStringLiteral( "Update Scene" ) );
 

src/3d/qgs3dmapscene.h

@@ -187,6 +187,24 @@ class _3D_EXPORT Qgs3DMapScene : public QObject
      */
     Qgs3DMapSettings *mapSettings() const { return &mMap; }
 
+    /**
+     * Returns whether updates of the 3D scene's entities are allowed.
+     * Normally, scene updates are enabled. But for debugging purposes,
+     * it may be useful to temporarily disable scene updates.
+     *
+     * \since QGIS 3.40
+     */
+    bool hasSceneUpdatesEnabled() const { return mSceneUpdatesEnabled; }
+
+    /**
+     * Sets whether updates of the 3D scene's entities are allowed.
+     * Normally, scene updates are enabled. But for debugging purposes,
+     * it may be useful to temporarily disable scene updates.
+     *
+     * \since QGIS 3.40
+     */
+    void setSceneUpdatesEnabled( bool enabled ) { mSceneUpdatesEnabled = enabled; }
+
     /**
      * Returns a map of 3D map scenes (by name) open in the QGIS application.
      *
@@ -302,5 +320,7 @@ class _3D_EXPORT Qgs3DMapScene : public QObject
     //! 3d axis visualization
     Qgs3DAxis *m3DAxis = nullptr;
 
+    bool mSceneUpdatesEnabled = true;
+
 };
 #endif // QGS3DMAPSCENE_H