The system can now focus previous, next

backends/x/entity.go

@@ -30,8 +30,10 @@ func (backend *Backend) NewEntity (owner tomo.Element) tomo.Entity {
 
 func (ent *entity) unlink () {
 	ent.propagate (func (child *entity) bool {
-		child.window = nil
+		if child.window != nil {
 			delete(ent.window.system.drawingInvalid, child)
+		}
+		child.window = nil
 		return true
 	})
 
@@ -61,17 +63,19 @@ func (ent *entity) setWindow (window *window) {
 	})
 }
 
-func (entity *entity) propagate (callback func (*entity) bool) {
+func (entity *entity) propagate (callback func (*entity) bool) bool {
 	for _, child := range entity.children {
-		if !callback(child) { break }
+		if !child.propagate(callback) {
-		child.propagate(callback)
+			return false
 		}
 	}
+	return callback(entity)
+}
 
 func (entity *entity) childAt (point image.Point) *entity {
 	for _, child := range entity.children {
 		if point.In(child.bounds) {
-			return child
+			return child.childAt(point)
 		}
 	}
 	return entity
@@ -190,12 +194,7 @@ func (entity *entity) Focused () bool {
 
 func (entity *entity) Focus () {
 	if entity.window == nil { return }
-	previous := entity.window.focused
+	entity.window.system.focus(entity)
-	entity.window.focused = entity
-	if previous != nil {
-		previous.element.(tomo.Focusable).HandleFocusChange()
-	}
-	entity.element.(tomo.Focusable).HandleFocusChange()
 }
 
 func (entity *entity) FocusNext () {

backends/x/system.go

@@ -62,12 +62,55 @@ func (system *system) SetConfig (config tomo.Config) {
 	})
 }
 
+func (system *system) focus (entity *entity) {
+	previous := system.focused
+	system.focused = entity
+	if previous != nil {
+		previous.element.(tomo.Focusable).HandleFocusChange()
+	}
+	if entity != nil {
+		entity.element.(tomo.Focusable).HandleFocusChange()
+	}
+}
+
 func (system *system) focusNext () {
-	// TODO
+	found   := system.focused == nil
+	focused := false
+	system.propagate (func (entity *entity) bool {
+		if found {
+			// looking for the next element to select
+			child, ok := entity.element.(tomo.Focusable)
+			if ok && child.Enabled() {
+				// found it
+				entity.Focus()
+				focused = true
+				return false
+			}
+		} else {
+			// looking for the current focused element
+			if entity == system.focused {
+				// found it
+				found = true
+			}
+		}
+		return true
+	})
+
+	if !focused { system.focus(nil) }
 }
 
 func (system *system) focusPrevious () {
-	// TODO
+	var behind *entity
+	system.propagate (func (entity *entity) bool {
+		if entity == system.focused {
+			return false
+		}
+
+		child, ok := entity.element.(tomo.Focusable)
+		if ok && child.Enabled() { behind = entity }
+		return true
+	})
+	system.focus(behind)
 }
 
 func (system *system) propagate (callback func (*entity) bool) {

element.go

@@ -37,6 +37,9 @@ type Container interface {
 type Focusable interface {
 	Element
 
+	// Enabled returns whether or not the element can currently accept focus.
+	Enabled () bool
+
 	// HandleFocusChange is called when the element is focused or unfocused.
 	HandleFocusChange ()
 }