[ui] Viewer3D: add loading overlay with BusyIndicator

meshroom/ui/qml/Viewer3D/MediaLibrary.qml

@@ -16,6 +16,15 @@ Entity {
     property bool pickingEnabled: false
     readonly property alias count: instantiator.count // number of instantiated media delegates
 
+    /// True while at least one media is being loaded
+    readonly property bool loading: {
+        for(var i=0; i<m.mediaModel.count; ++i) {
+            if(m.mediaModel.get(i).status === SceneLoader.Loading)
+                return true;
+        }
+        return false;
+    }
+
     signal pressed(var pick)
     signal loadRequest(var idx)
 

meshroom/ui/qml/Viewer3D/Viewer3D.qml

@@ -214,6 +214,19 @@ FocusScope {
         }
     }
 
+    // Media loading overlay
+    // (Scene3D is frozen while a media is being loaded)
+    Rectangle {
+        anchors.fill: parent
+        visible: mediaLibrary.loading
+        color: Qt.darker(Colors.sysPalette.mid, 1.2)
+        opacity: 0.6
+        BusyIndicator {
+            anchors.centerIn: parent
+            running: parent.visible
+        }
+    }
+
     //  UI Overlay
     Controls1.SplitView {
         id: overlaySplitView