More efficiant roomList delegate in view detection

src/gui/MainPane/AccountRoomsDelegate.qml

@@ -45,20 +45,15 @@ Column {
 
         delegate: HLoader {
             asynchronous: false
-            active: firstSyncDone && inView
+            active: index === 0 || (
+                roomList.firstDelegateHeight !== 0 &&
+                index >= roomList.firstIndexInView &&
+                index <= roomList.lastIndexInView
+            )
 
             width: roomList.width
             height: roomList.firstDelegateHeight
 
-            // XXX: these assume the view has no spacing/margins/header/footer
-            readonly property int yTop:
-                accountRooms.y + account.height + accountRooms.spacing +
-                model.index * height
-            readonly property int yBottom: yTop + height
-            readonly property bool inView:
-                yBottom >= mainPaneList.contentY &&
-                yTop <= mainPaneList.contentY + mainPaneList.height
-
             readonly property var sourceModel: model
 
             sourceComponent: Room {
@@ -71,7 +66,9 @@ Column {
 
         highlight: null  // managed by the AccountRoomsList
 
-        onFirstDelegateHeightChanged: firstDelegateHeight = firstDelegateHeight
+        onFirstDelegateHeightChanged:
+            if (firstDelegateHeight !== 0)
+                firstDelegateHeight = firstDelegateHeight
 
 
         // Delete 0 must *always* be loaded, and all delegates must have the
@@ -81,6 +78,14 @@ Column {
             contentItem.visibleChildren[0].implicitHeight :
             0
 
+        readonly property int firstIndexInView:
+            (mainPaneList.contentY - account.height - accountRooms.spacing) /
+            firstDelegateHeight -
+            accountRooms.y / firstDelegateHeight
+
+        readonly property int lastIndexInView:
+            firstIndexInView + mainPaneList.height / firstDelegateHeight
+
         readonly property bool hasActiveRoom:
             window.uiState.page === "Pages/Chat/Chat.qml" &&
             window.uiState.pageProperties.userId === userId

src/gui/MainPane/Room.qml

@@ -13,9 +13,9 @@ HTileDelegate {
     opacity:
         model.left ? theme.mainPane.listView.room.leftRoomOpacity : 1
 
-    topPadding: theme.spacing / (model.index === 0 ? 1 : 1.5)
+    // topPadding: theme.spacing / (model.index === 0 ? 1 : 1.5)
-    bottomPadding:
+    // bottomPadding:
-        theme.spacing / (model.index === view.count - 1 ? 1 : 1.5)
+    //     theme.spacing / (model.index === view.count - 1 ? 1 : 1.5)
     leftPadding: theme.spacing * 2
     rightPadding: theme.spacing