feat(tracker/gioui): add scrollbars to menus

CHANGELOG.md

@@ -5,6 +5,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ## Unreleased
 ### Added
+- Scroll bars to menus, shown when a menu is too long to fit.
 - Save the GUI state periodically to a recovery file and load it on
   startup of the app, if present. The recovery files are located in the
   app config directory (e.g. AppData/Roaming/Sointu on Windows).

tracker/gioui/menu.go

@@ -21,6 +21,7 @@ type Menu struct {
 	clicks    []int
 	hover     int
 	list      layout.List
+	scrollBar ScrollBar
 }
 
 type MenuStyle struct {
@@ -80,6 +81,9 @@ func (m *MenuStyle) Layout(gtx C, items ...MenuItem) D {
 			}
 		}
 		m.Menu.list.Axis = layout.Vertical
+		m.Menu.scrollBar.Axis = layout.Vertical
+		return layout.Stack{Alignment: layout.SE}.Layout(gtx,
+			layout.Expanded(func(gtx C) D {
 				return m.Menu.list.Layout(gtx, len(items), func(gtx C, i int) D {
 					defer op.Offset(image.Point{}).Push(gtx.Ops).Pop()
 					var macro op.MacroOp
@@ -130,6 +134,11 @@ func (m *MenuStyle) Layout(gtx C, items ...MenuItem) D {
 					}
 					return dims
 				})
+			}),
+			layout.Expanded(func(gtx C) D {
+				return m.Menu.scrollBar.Layout(gtx, unit.Dp(10), len(items), &m.Menu.list.Position)
+			}),
+		)
 	}
 	popup := Popup(&m.Menu.Visible)
 	popup.NE = unit.Dp(0)