backends/x/window.go

@@ -261,6 +261,20 @@ func (window *Window) childSelectionRequestCallback () (granted bool) {
 	return true
 }
 
+func (window *Window) childSelectionMotionRequestCallback (
+	direction tomo.SelectionDirection,
+) (
+	granted bool,
+) {
+	if child, ok := window.child.(tomo.Selectable); ok {
+		if !child.HandleSelection(direction) {
+			child.HandleDeselection()
+		}
+		return true
+	}
+	return true
+}
+
 func (window *Window) pushRegion (region image.Rectangle) {
 	if window.xCanvas == nil { panic("whoopsie!!!!!!!!!!!!!!") }
 	image, ok := window.xCanvas.SubImage(region).(*xgraphics.Image)

element.go

@@ -3,7 +3,8 @@ package tomo
 // ParentHooks is a struct that contains callbacks that let child elements send
 // information to their parent element without the child element knowing
 // anything about the parent element or containing any reference to it. When a
-// parent element adopts a child element, it must set these callbacks.
+// parent element adopts a child element, it must set these callbacks. They are
+// allowed to be nil.
 type ParentHooks struct {
 	// Draw is called when a part of the child element's surface is updated.
 	// The updated region will be passed to the callback as a sub-image.
@@ -20,6 +21,10 @@ type ParentHooks struct {
 	// request, it must send the child element a selection event and return
 	// true.
 	SelectionRequest func () (granted bool)
+
+	// SelectionMotionRequest is called when the child element wants the
+	// parent element to select the previous/next element in relation to it.
+	SelectionMotionRequest func (direction SelectionDirection) (granted bool)
 }
 
 // RunDraw runs the Draw hook if it is not nil. If it is nil, it does nothing.
@@ -46,6 +51,19 @@ func (hooks ParentHooks) RunSelectionRequest () (granted bool) {
 	return
 }
 
+// RunSelectionMotionRequest runs the SelectionMotionRequest hook if it is not
+// nil. If it is nil, it does nothing.
+func (hooks ParentHooks) RunSelectionMotionRequest (
+	direction SelectionDirection,
+) (
+	granted bool,
+) {
+	if hooks.SelectionMotionRequest != nil {
+		granted = hooks.SelectionMotionRequest(direction)
+	}
+	return
+}
+
 // Element represents a basic on-screen object.
 type Element interface {
 	// Element must implement the Canvas interface. Elements should start

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) {
+		SelectionMotionRequest: func (
-			element.drawChildRegion(child, region)
+			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) {