1 files changed, 38 insertions, 2 deletions
diff --git a/go/ui/widget.go b/go/ui/widget.go
index c8fb0816..d783eb36 100644
--- a/go/ui/widget.go
+++ b/go/ui/widget.go
@@ -5,6 +5,42 @@ import (
 )
 
 type Widget interface {
-	Draw(screen *ebiten.Image)
-	FindObjectAt(x, y int) interface{}
+	Draw(*ebiten.Image)
+	FindObjectAt(int, int) interface{}
+}
+
+type WidgetBase struct {
+	X, Y          int
+	Width, Height int
+	img           *ebiten.Image
+	renderImpl    func() *ebiten.Image
+}
+
+func renderDummy() *ebiten.Image {
+	return nil
+}
+
+func NewWidgetBase(x, y, width, height int) WidgetBase {
+	return WidgetBase{x, y, width, height, nil, renderDummy}
+}
+
+func (w *WidgetBase) Draw(screen *ebiten.Image) {
+	if w.img == nil {
+		w.img = w.renderImpl()
+	}
+	op := &ebiten.DrawImageOptions{}
+	op.GeoM.Translate(float64(w.X), float64(w.Y))
+	screen.DrawImage(w.img, op)
+}
+
+func (w *WidgetBase) ForceRedraw() {
+	w.img = nil
+}
+
+func (w *WidgetBase) Contains(x, y int) bool {
+	return x >= 0 && y >= 0 && x >= w.X && x <= w.X+w.Width && y >= w.Y && y <= w.Y+w.Height
+}
+
+func (w *WidgetBase) FindObjectAt(int, int) interface{} {
+	return nil
 }