Made this crazy selection system

backends/x/entity.go

@@ -15,6 +15,7 @@ type entity struct {
 	minWidth      int
 	minHeight     int
 
+	selected      bool
 	layoutInvalid bool
 	isContainer   bool
 }
@@ -42,6 +43,11 @@ func (ent *entity) unlink () {
 	}
 	ent.parent = nil
 	ent.window = nil
+	
+	if element, ok := ent.element.(tomo.Selectable); ok {
+		ent.selected = false
+		element.HandleSelectionChange()
+	}
 }
 
 func (entity *entity) link (parent *entity) {
@@ -96,6 +102,14 @@ func (entity *entity) scrollTargetChildAt (point image.Point) *entity {
 	return nil
 }
 
+func (entity *entity) forMouseTargetContainers (callback func (tomo.MouseTargetContainer)) {
+	if entity.parent == nil { return }
+	if parent, ok := entity.parent.element.(tomo.MouseTargetContainer); ok {
+		callback(parent)
+	}
+	entity.parent.forMouseTargetContainers(callback)
+}
+
 // ----------- Entity ----------- //
 
 func (entity *entity) Invalidate () {
@@ -195,6 +209,14 @@ func (entity *entity) PlaceChild (index int, bounds image.Rectangle) {
 	child.InvalidateLayout()
 }
 
+func (entity *entity) SelectChild (index int, selected bool) {
+	child := entity.children[index]
+	if element, ok := entity.element.(tomo.Selectable); ok {
+		child.selected = selected
+		element.HandleSelectionChange()
+	}
+}
+
 func (entity *entity) ChildMinimumSize (index int) (width, height int) {
 	childEntity := entity.children[index]
 	return childEntity.minWidth, childEntity.minHeight
@@ -220,6 +242,12 @@ func (entity *entity) FocusPrevious () {
 	entity.window.system.focusPrevious()
 }
 
+// ----------- SelectableEntity ----------- //
+
+func (entity *entity) Selected () bool {
+	return entity.selected
+}
+
 // ----------- FlexibleEntity ----------- //
 
 func (entity *entity) NotifyFlexibleHeightChange () {

backends/x/event.go

@@ -206,12 +206,19 @@ func (window *window) handleButtonPress (
 		}
 	} else {
 		underneath := window.system.childAt(point)
+		window.system.drags[buttonEvent.Detail] = underneath
 		if child, ok := underneath.element.(tomo.MouseTarget); ok {
-			window.system.drags[buttonEvent.Detail] = child
 			child.HandleMouseDown (
 				point.X, point.Y,
 				input.Button(buttonEvent.Detail))
 		}
+		callback := func (container tomo.MouseTargetContainer) {
+			container.HandleChildMouseDown (
+				point.X, point.Y,
+				input.Button(buttonEvent.Detail),
+				underneath.element)
+		}
+		underneath.forMouseTargetContainers(callback)
 	}
 	
 	window.system.afterEvent()
@@ -223,12 +230,22 @@ func (window *window) handleButtonRelease (
 ) {
 	buttonEvent := *event.ButtonReleaseEvent
 	if buttonEvent.Detail >= 4 && buttonEvent.Detail <= 7 { return }
-	child := window.system.drags[buttonEvent.Detail]
-	if child != nil {
-		child.HandleMouseUp (
+	dragging := window.system.drags[buttonEvent.Detail]
+	if dragging != nil {
+		if child, ok := dragging.element.(tomo.MouseTarget); ok {
+			child.HandleMouseUp (
+				int(buttonEvent.EventX),
+				int(buttonEvent.EventY),
+				input.Button(buttonEvent.Detail))
+		}
+		callback := func (container tomo.MouseTargetContainer) {
+			container.HandleChildMouseUp (
 			int(buttonEvent.EventX),
 			int(buttonEvent.EventY),
-			input.Button(buttonEvent.Detail))
+			input.Button(buttonEvent.Detail),
+			dragging.element)
+		}
+		dragging.forMouseTargetContainers(callback)
 	}
 	
 	window.system.afterEvent()
@@ -244,7 +261,7 @@ func (window *window) handleMotionNotify (
 
 	handled := false
 	for _, child := range window.system.drags {
-		if child, ok := child.(tomo.MotionTarget); ok {
+		if child, ok := child.element.(tomo.MotionTarget); ok {
 			child.HandleMotion(x, y)
 			handled = true
 		}

backends/x/system.go

@@ -33,7 +33,7 @@ type system struct {
 	drawingInvalid   entitySet
 	anyLayoutInvalid bool
 	
-	drags [10]tomo.MouseTarget
+	drags [10]*entity
 
 	pushFunc func (image.Rectangle)
 }

element.go

@@ -40,17 +40,43 @@ type Container interface {
 	HandleChildMinimumSizeChange (child Element)
 }
 
+// Enableable represents an element that can be enabled and disabled. Disabled
+// elements typically appear greyed out.
+type Enableable interface {
+	Element
+
+	// Enabled returns whether or not the element is enabled.
+	Enabled () bool
+	
+	// SetEnabled sets whether or not the element is enabled.
+	SetEnabled (bool)
+}
+
 // Focusable represents an element that has keyboard navigation support.
 type Focusable interface {
 	Element
-
-	// Enabled returns whether or not the element can currently accept focus.
-	Enabled () bool
+	Enableable
 
 	// HandleFocusChange is called when the element is focused or unfocused.
 	HandleFocusChange ()
 }
 
+// Selectable represents an element that can be selected. This includes things
+// like list items, files, etc. The difference between this and Focusable is
+// that multiple Selectable elements may be selected at the same time, whereas
+// only one Focusable element may be focused at the same time. Containers who's
+// purpose is to contain selectable elements can determine when to select them
+// by implementing MouseTargetContainer and listening for HandleChildMouseDown
+// events.
+type Selectable interface {
+	Element
+	Enableable
+
+	// HandleSelectionChange is called when the element is selected or
+	// deselected.
+	HandleSelectionChange ()
+}
+
 // KeyboardTarget represents an element that can receive keyboard input.
 type KeyboardTarget interface {
 	Element
@@ -80,6 +106,22 @@ type MouseTarget interface {
 	HandleMouseUp (x, y int, button input.Button)
 }
 
+// MouseTargetContainer represents an element that wants to know when one
+// of its children is clicked. Children do not have to implement MouseTarget for
+// a container satisfying MouseTargetContainer to be notified that they have
+// been clicked.
+type MouseTargetContainer interface {
+	Container
+
+	// HandleMouseDown is called when a mouse button is pressed down on a
+	// child element.
+	HandleChildMouseDown (x, y int, button input.Button, child Element)
+
+	// HandleMouseUp is called when a mouse button is released that was
+	// originally pressed down on a child element.
+	HandleChildMouseUp (x, y int, button input.Button, child Element)
+}
+
 // MotionTarget represents an element that can receive mouse motion events.
 type MotionTarget interface {
 	Element

elements/entry.go

@@ -0,0 +1,142 @@
+package elements
+
+import "git.tebibyte.media/sashakoshka/tomo"
+import "git.tebibyte.media/sashakoshka/tomo/canvas"
+import "git.tebibyte.media/sashakoshka/tomo/artist"
+import "git.tebibyte.media/sashakoshka/tomo/default/theme"
+
+type cellEntity interface {
+	tomo.ContainerEntity
+	tomo.SelectableEntity
+}
+
+// Cell is a single-element container that satisfies tomo.Selectable. It
+// provides styling based on whether or not it is selected.
+type Cell struct {
+	entity   cellEntity
+	child    tomo.Element
+	enabled  bool
+	padding  bool
+	theme    theme.Wrapped
+}
+
+// NewCell creates a new cell element. If padding is true, the cell will have
+// padding on all sides. Child can be nil and added later with the Adopt()
+// method.
+func NewCell (child tomo.Element, padding bool) (element *Cell) {
+	element = &Cell { padding: padding }
+	element.theme.Case = tomo.C("tomo", "cell")
+	element.entity = tomo.NewEntity(element).(cellEntity)
+	element.Adopt(child)
+	return
+}
+
+// Entity returns this element's entity.
+func (element *Cell) Entity () tomo.Entity {
+	return element.entity
+}
+
+// Draw causes the element to draw to the specified destination canvas.
+func (element *Cell) Draw (destination canvas.Canvas) {
+	bounds  := element.entity.Bounds()
+	pattern := element.theme.Pattern(tomo.PatternTableCell, element.state())
+	if element.child == nil {
+		pattern.Draw(destination, bounds)
+	} else if element.padding {
+		artist.DrawShatter (
+			destination, pattern, bounds,
+			element.child.Entity().Bounds())
+	}
+}
+
+// Draw causes the element to perform a layout operation.
+func (element *Cell) Layout () {
+	if element.child == nil { return }
+	
+	bounds := element.entity.Bounds()
+	if element.padding {
+		bounds = element.theme.Padding(tomo.PatternTableCell).Apply(bounds)
+	}
+
+	element.entity.PlaceChild(0, bounds)
+}
+
+// DrawBackground draws this element's background pattern to the specified
+// destination canvas.
+func (element *Cell) DrawBackground (destination canvas.Canvas) {
+	element.theme.Pattern(tomo.PatternTableCell, element.state()).
+		Draw(destination, element.entity.Bounds())
+}
+
+// Adopt sets this element's child. If nil is passed, any child is removed.
+func (element *Cell) Adopt (child tomo.Element) {
+	if element.child != nil {
+		element.entity.Disown(element.entity.IndexOf(element.child))
+	}
+	if child != nil {
+		element.entity.Adopt(child)
+	}
+	element.child = child
+
+	element.updateMinimumSize()
+	element.entity.Invalidate()
+	element.entity.InvalidateLayout()
+}
+
+// Enabled returns whether this cell is enabled or not.
+func (element *Cell) Enabled () bool {
+	return element.enabled
+}
+
+// SetEnabled sets whether this cell can be selected or not.
+func (element *Cell) SetEnabled (enabled bool) {
+	if element.enabled == enabled { return }
+	element.enabled = enabled
+	element.entity.Invalidate()
+	if child, ok := element.child.(tomo.Enableable); ok {
+		child.SetEnabled(enabled)
+	}
+}
+
+// SetTheme sets this element's theme.
+func (element *Cell) SetTheme (theme tomo.Theme) {
+	if theme == element.theme.Theme { return }
+	element.theme.Theme = theme
+	element.updateMinimumSize()
+	element.entity.Invalidate()
+	element.entity.InvalidateLayout()
+}
+
+func (element *Cell) HandleSelectionChange () {
+	element.entity.Invalidate()
+}
+
+func (element *Cell) HandleChildMinimumSizeChange (tomo.Element) {
+	element.updateMinimumSize()
+	element.entity.Invalidate()
+	element.entity.InvalidateLayout()
+}
+
+func (element *Cell) state () tomo.State {
+	return tomo.State {
+		Disabled: !element.enabled,
+		On:       element.entity.Selected(),
+	}
+}
+
+func (element *Cell) updateMinimumSize () {
+	width, height := 0, 0
+
+	if element.child != nil {
+		childWidth, childHeight := element.entity.ChildMinimumSize(0)
+		width  += childWidth
+		height += childHeight
+	}
+	if element.padding {
+		padding := element.theme.Padding(tomo.PatternTableCell)
+		width  += padding.Horizontal()
+		height += padding.Vertical()
+	}
+	
+	element.entity.SetMinimumSize(width, height)
+}

entity.go

@@ -69,6 +69,10 @@ type ContainerEntity interface {
 	// index to a bounding rectangle.
 	PlaceChild (index int, bounds image.Rectangle)
 
+	// SelectChild marks a child as selected or unselected, if it is
+	// selectable.
+	SelectChild (index int, selected bool)
+
 	// ChildMinimumSize returns the minimum size of the child at the
 	// specified index.
 	ChildMinimumSize (index int) (width, height int)
@@ -94,6 +98,14 @@ type FocusableEntity interface {
 	FocusPrevious ()
 }
 
+// SelectableEntity is given to elements that support the Selectable interface.
+type SelectableEntity interface {
+	Entity
+
+	// Selected returns whether this element is currently selected.
+	Selected () bool
+}
+
 // FlexibleEntity is given to elements that support the Flexible interface.
 type FlexibleEntity interface {
 	Entity