2 files changed, 111 insertions, 0 deletions
diff --git a/lib/ui/grid.go b/lib/ui/grid.go
index 3c375ee..5fe6ab2 100644
--- a/lib/ui/grid.go
+++ b/lib/ui/grid.go
@@ -5,6 +5,7 @@ import (
 	"math"
 )
 
+// A container which arranges its children on a grid.
 type Grid struct {
 	rows         []GridSpec
 	rowLayout    []gridLayout
diff --git a/lib/ui/list.go b/lib/ui/list.go
new file mode 100644
index 0000000..58f304f
--- /dev/null
+++ b/lib/ui/list.go
@@ -0,0 +1,110 @@
+package ui
+
+import (
+	"fmt"
+)
+
+// A container which arranges its children in a list.
+type List struct {
+	Items        []*ListItem
+	itemHeight   int
+	onInvalidate func(d Drawable)
+	selected     int
+}
+
+type ListItem struct {
+	Content Drawable
+	invalid bool
+}
+
+type SelectableDrawable interface {
+	Drawable
+	DrawWithSelected(ctx *Context, selected bool)
+}
+
+func NewList() *List {
+	return &List{itemHeight: 1, selected: -1}
+}
+
+func (list *List) OnInvalidate(onInvalidate func(d Drawable)) {
+	list.onInvalidate = onInvalidate
+}
+
+func (list *List) Invalidate() {
+	for _, item := range list.Items {
+		item.Content.Invalidate()
+	}
+	if list.onInvalidate != nil {
+		list.onInvalidate(list)
+	}
+}
+
+func (list *List) Draw(ctx *Context) {
+	for i, item := range list.Items {
+		if !item.invalid {
+			continue
+		}
+		subctx := ctx.Subcontext(0, i, ctx.Width(), list.itemHeight)
+		if content, ok := item.Content.(SelectableDrawable); ok {
+			content.DrawWithSelected(subctx, i == list.selected)
+		} else {
+			item.Content.Draw(subctx)
+		}
+	}
+}
+
+func (list *List) Add(child Drawable) {
+	list.Items = append(list.Items, &ListItem{Content: child, invalid: true})
+	child.OnInvalidate(list.childInvalidated)
+	list.Invalidate()
+}
+
+func (list *List) Remove(child Drawable) {
+	for i, item := range list.Items {
+		if item.Content == child {
+			list.Items = append(list.Items[:i], list.Items[i+1:]...)
+			child.OnInvalidate(nil)
+			list.Invalidate()
+			return
+		}
+	}
+	panic(fmt.Errorf("Attempted to remove unknown child"))
+}
+
+func (list *List) Set(items []Drawable) {
+	for _, item := range list.Items {
+		item.Content.OnInvalidate(nil)
+	}
+	list.Items = make([]*ListItem, len(items))
+	for i, item := range items {
+		list.Items[i] = &ListItem{Content: item, invalid: true}
+		item.OnInvalidate(list.childInvalidated)
+	}
+	list.Invalidate()
+}
+
+func (list *List) Select(index int) {
+	if index >= len(list.Items) || index < 0 {
+		panic(fmt.Errorf("Attempted to select unknown child"))
+	}
+	list.selected = index
+	list.Invalidate()
+}
+
+func (list *List) ItemHeight(height int) {
+	list.itemHeight = height
+	list.Invalidate()
+}
+
+func (list *List) childInvalidated(child Drawable) {
+	for _, item := range list.Items {
+		if item.Content == child {
+			item.invalid = true
+			if list.onInvalidate != nil {
+				list.onInvalidate(list)
+			}
+			return
+		}
+	}
+	panic(fmt.Errorf("Attempted to invalidate unknown child"))
+}