Disable link loading animation when offscreen

Stop the link preview loading indicator animation running when the delegate isn't visible.

CCBUG: 465715

src/qml/Component/Timeline/LinkPreviewDelegate.qml

@@ -44,6 +44,11 @@ Loader {
      */
     property var defaultHeight : Kirigami.Units.gridUnit * 3 + Kirigami.Units.smallSpacing * 2
 
+    /**
+     * @brief Whether the loading indicator should animate if visible.
+     */
+    property bool indicatorEnabled: false
+
     active: !currentRoom.usesEncryption && model.display && links && links.length > 0
     visible: Config.showLinkPreview && active
     sourceComponent: linkPreviewer.loaded ? linkPreviewComponent : loadingComponent
@@ -129,7 +134,7 @@ Loader {
     Component {
         id: loadingComponent
         RowLayout {
-            property bool hovered: false
+            id: componentRoot
             property bool truncated: false
 
             Rectangle {
@@ -137,7 +142,9 @@ Loader {
                 width: Kirigami.Units.smallSpacing
                 color: Kirigami.Theme.highlightColor
             }
-            QQC2.BusyIndicator { }
+            QQC2.BusyIndicator {
+                running: root.indicatorEnabled
+            }
             Kirigami.Heading {
                 Layout.fillWidth: true
                 Layout.minimumHeight: root.defaultHeight

src/qml/Component/Timeline/MessageDelegate.qml

@@ -31,6 +31,7 @@ TimelineContainer {
         }
         LinkPreviewDelegate {
             Layout.fillWidth: true
+            indicatorEnabled: messageDelegate.isVisibleInTimeline()
         }
     }
 }

src/qml/Component/Timeline/TimelineContainer.qml

@@ -320,4 +320,9 @@ ColumnLayout {
 
         visible: eventType !== MessageEventModel.State && eventType !== MessageEventModel.Notice && reaction != undefined && reaction.length > 0
     }
+
+    function isVisibleInTimeline() {
+        let yoff = Math.round(y - ListView.view.contentY);
+        return (yoff + height > 0 && yoff < ListView.view.height)
+    }
 }