3D Viewer fix and optimization

src/FlyView/FlyView.qml

@@ -18,7 +18,8 @@ import QGroundControl.Viewer3D
 Item {
     id: _root
 
-    readonly property bool _is3DMode: QGCViewer3DManager.displayMode === QGCViewer3DManager.View3D
+    readonly property bool _is3DMode:       QGCViewer3DManager.displayMode === QGCViewer3DManager.View3D
+    readonly property bool _keepSceneAlive: QGroundControl.settingsManager.viewer3DSettings.keepSceneAlive.rawValue
 
     // These should only be used by MainRootWindow
     property var planController:    _planController
@@ -157,15 +158,24 @@ Item {
         }
 
         Loader {
-            id:             viewer3DLoader
-            z:              1
-            anchors.fill:   parent
-            active:         _is3DMode
-
-            onActiveChanged: {
-                if (active) {
-                    setSource("qrc:/qml/QGroundControl/Viewer3D/Models3D/Viewer3DModel.qml",
-)
+            id:           viewer3DLoader
+            z:            1
+            anchors.fill: parent
+            visible:      _is3DMode
+        }
+
+        Connections {
+            target: QGCViewer3DManager
+            function onDisplayModeChanged() {
+                if (QGCViewer3DManager.displayMode === QGCViewer3DManager.View3D) {
+                    if (!viewer3DLoader.item) {
+                        viewer3DLoader.setSource(
+                            "qrc:/qml/QGroundControl/Viewer3D/Models3D/Viewer3DModel.qml",
+                            { missionController: Qt.binding(() => _missionController) }
+                        )
+                    }
+                } else if (!_keepSceneAlive) {
+                    viewer3DLoader.source = ""
                 }
             }
         }

src/Settings/Viewer3D.SettingsGroup.json

@@ -49,6 +49,14 @@
             "default": 0,
             "label": "Altitude bias for vehicles in the 3D View",
             "keywords": "altitude bias,3d data"
+        },
+        {
+            "name": "keepSceneAlive",
+            "shortDesc": "Keep the 3D scene loaded in memory when switching back to fly view. Disable on memory-constrained devices.",
+            "type": "bool",
+            "default": true,
+            "label": "Keep 3D scene alive when exiting 3D view",
+            "keywords": "3d view,memory,scene,alive"
         }
     ]
 }

src/Settings/Viewer3DSettings.cc

@@ -9,3 +9,4 @@ DECLARE_SETTINGSFACT(Viewer3DSettings, mapProvider)
 DECLARE_SETTINGSFACT(Viewer3DSettings, osmFilePath)
 DECLARE_SETTINGSFACT(Viewer3DSettings, buildingLevelHeight)
 DECLARE_SETTINGSFACT(Viewer3DSettings, altitudeBias)
+DECLARE_SETTINGSFACT(Viewer3DSettings, keepSceneAlive)

src/Settings/Viewer3DSettings.h

@@ -24,4 +24,5 @@ class Viewer3DSettings : public SettingsGroup
     DEFINE_SETTINGFACT(osmFilePath)
     DEFINE_SETTINGFACT(buildingLevelHeight)
     DEFINE_SETTINGFACT(altitudeBias)
+    DEFINE_SETTINGFACT(keepSceneAlive)
 };

src/UI/AppSettings/pages/Viewer3D.SettingsUI.json

@@ -11,6 +11,9 @@
                 },
                 {
                     "setting": "viewer3DSettings.mapProvider"
+                },
+                {
+                    "setting": "viewer3DSettings.keepSceneAlive"
                 }
             ]
         },

src/Viewer3D/Viewer3DQml/Models3D/Viewer3DVehicleItems.qml

@@ -163,7 +163,11 @@ Node {
 
     ListModel {
         id: missionWaypointListModel
+    }
 
+    Component.onDestruction: {
+        // This is necessary insurance to prevent crashes after destruction when "keepSceneAlive" setting is disabled.
+        missionWaypointListModel.clear()
     }
 
     DroneModelDjiF450 {