qml: implement scrollbar drag in history listview

electrum/gui/qml/components/Constants.qml

@@ -32,4 +32,7 @@ Item {
     property color colorLightningLocal: "blue"
     property color colorLightningRemote: "yellow"
 
+    function colorAlpha(baseColor, alpha) {
+        return Qt.rgba(baseColor.r, baseColor.g, baseColor.b, alpha)
+    }
 }

electrum/gui/qml/components/History.qml

@@ -10,7 +10,8 @@ import "controls"
 
 Pane {
     id: rootItem
-    visible: Daemon.currentWallet !== undefined
+    visible: Daemon.currentWallet
+    padding: 0
     clip: true
 
     ListView {
@@ -62,6 +63,48 @@ Pane {
 
     }
 
+    MouseArea {
+        id: vdragscroll
+        anchors {
+            top: listview.top
+            right: listview.right
+            bottom: listview.bottom
+        }
+        width: constants.paddingXXLarge
+        drag.target: dragb
+        onPressedChanged: if (pressed) {
+            dragb.y = mouseY - dragb.height/2
+        }
+    }
+
+    Rectangle {
+        id: dragb
+        anchors.right: vdragscroll.left
+        width: postext.width + constants.paddingXXLarge
+        height: postext.height + constants.paddingXXLarge
+        radius: constants.paddingXSmall
+
+        color: constants._alpha(Material.accentColor, 0.33)
+        border.color: Material.accentColor
+        opacity : vdragscroll.drag.active ? 1 : 0
+        Behavior on opacity { NumberAnimation { duration: 300 } }
+
+        onYChanged: {
+            if (vdragscroll.drag.active) {
+                listview.contentY =
+                    Math.min(listview.contentHeight - listview.height + listview.originY,
+                    Math.max(listview.originY,
+                        (y/vdragscroll.height) * listview.contentHeight))
+            }
+        }
+        Label {
+            id: postext
+            anchors.centerIn: parent
+            text: listview.itemAt(0,listview.contentY + (dragb.y + dragb.height/2)).delegateModel.date
+            font.pixelSize: constants.fontSizeLarge
+        }
+    }
+
     Connections {
         target: Network
         function onHeightChanged(height) {

electrum/gui/qml/components/controls/HistoryItemDelegate.qml

@@ -10,6 +10,9 @@ Item {
     width: ListView.view.width
     height: delegateLayout.height
 
+    // expose delegate model for scroll indicator
+    property var delegateModel: model
+
     ColumnLayout {
         id: delegateLayout
         width: parent.width