Allow widgets to specify whether they accept focus

box.go

@@ -12,8 +12,6 @@ type Box struct {
 
 	children []Widget
 
-	focus bool
-
 	sync.Mutex
 }
 
@@ -35,12 +33,12 @@ func (b *Box) SetRect(r image.Rectangle) {
 	b.rect = r
 }
 
-func (b *Box) SetFocus(focus bool) {
-	b.focus = focus
+func (b *Box) SetFocus(focus bool) bool {
+	return false
 }
 
 func (b *Box) Focus() bool {
-	return b.focus
+	return false
 }
 
 func (b *Box) HandleKeyboardEvent(key ebiten.Key, r rune) (handled bool, err error) {

game.go

@@ -30,13 +30,14 @@ func SetRoot(w Widget) {
 }
 
 func SetFocus(w Widget) {
-	if focusedWidget != nil {
-		focusedWidget.SetFocus(false)
+	lastFocused := focusedWidget
+	if w != nil && !w.SetFocus(true) {
+		return
+	}
+	if lastFocused != nil && lastFocused != w {
+		lastFocused.SetFocus(false)
 	}
 	focusedWidget = w
-	if w != nil {
-		w.SetFocus(true)
-	}
 }
 
 func Focused() Widget {

input.go

@@ -11,6 +11,7 @@ type Input struct {
 	*Box
 	Field  *messeji.InputField
 	Cursor string
+	focus  bool
 }
 
 func NewInput(prefix string, text string, onSelected func(text string) (handled bool)) *Input {
@@ -57,7 +58,7 @@ func (i *Input) SetRect(r image.Rectangle) {
 	i.Field.SetRect(r)
 }
 
-func (i *Input) SetFocus(focus bool) {
+func (i *Input) SetFocus(focus bool) bool {
 	i.focus = focus
 
 	var cursor string
@@ -65,6 +66,11 @@ func (i *Input) SetFocus(focus bool) {
 		cursor = i.Cursor
 	}
 	i.Field.SetSuffix(cursor)
+	return true
+}
+
+func (i *Input) Focused() bool {
+	return i.focus
 }
 
 func (i *Input) HandleMouse(cursor image.Point, pressed bool, clicked bool) (handled bool, err error) {

text.go

@@ -26,8 +26,12 @@ func NewText(text string) *Text {
 	}
 }
 
-func (t *Text) SetFocus(focus bool) {
-	// Do nothing.
+func (t *Text) SetFocus(focus bool) bool {
+	return false
+}
+
+func (t *Text) Focus() bool {
+	return false
 }
 
 func (t *Text) Children() []Widget {

widget.go

@@ -9,7 +9,7 @@ import (
 type Widget interface {
 	Rect() image.Rectangle
 	SetRect(r image.Rectangle)
-	SetFocus(focus bool)
+	SetFocus(focus bool) (accept bool)
 	HandleMouse(cursor image.Point, pressed bool, clicked bool) (handled bool, err error)
 	HandleKeyboard() (handled bool, err error)
 	HandleKeyboardEvent(ebiten.Key, rune) (handled bool, err error)