Selectable elements can now request the selection to be moved

elements/basic/button.go

@@ -103,6 +103,7 @@ func (element *Button) HandleSelection (
 ) (
 	accepted bool,
 ) {
+	direction = direction.Canon()
 	if !element.enabled { return false }
 	if element.selected && direction != tomo.SelectionDirectionNeutral {
 		return false

elements/basic/container.go

@@ -43,6 +43,9 @@ func (element *Container) SetLayout (layout tomo.Layout) {
 // whatever way is defined by the current layout.
 func (element *Container) Adopt (child tomo.Element, expand bool) {
 	child.SetParentHooks (tomo.ParentHooks {
+		Draw: func (region tomo.Canvas) {
+			element.drawChildRegion(child, region)
+		},
 		MinimumSizeChange: func (int, int) {
 			element.updateMinimumSize()
 		},
@@ -51,8 +54,12 @@ func (element *Container) Adopt (child tomo.Element, expand bool) {
 			if !selectable { return }
 			return element.childSelectionRequestCallback(child)
 		},
-		Draw: func (region tomo.Canvas) {
-			element.drawChildRegion(child, region)
+		SelectionMotionRequest: func (
+			direction tomo.SelectionDirection,
+		) (
+			granted bool,
+		) {
+			return element.core.RequestSelectionMotion(direction)
 		},
 	})
 	element.children = append (element.children, tomo.LayoutEntry {

elements/core/core.go

@@ -80,6 +80,18 @@ func (control CoreControl) RequestSelection () (granted bool) {
 	return control.core.hooks.RunSelectionRequest()
 }
 
+// RequestSelectionMotion requests that the element's parent deselect this
+// element and select the one to the left or right of it, depending on the
+// direction. If the requests was granted, it returns true. If it was denied, it
+// returns false.
+func (control CoreControl) RequestSelectionMotion (
+	direction tomo.SelectionDirection,
+) (
+	granted bool,
+) {
+	return control.core.hooks.RunSelectionMotionRequest(direction)
+}
+
 // HasImage returns true if the core has an allocated image buffer, and false if
 // it doesn't.
 func (control CoreControl) HasImage () (has bool) {