Merge pull request 'atomize-parent-hooks' (#4) from atomize-parent-hooks into main

Reviewed-on: sashakoshka/tomo#4

backends/x/event.go

@@ -122,7 +122,7 @@ func (window *Window) handleButtonPress (
 			sum := scrollSum { }
 			sum.add(buttonEvent.Detail)
 			window.compressScrollSum(buttonEvent, &sum)
-			child.HandleScroll (
+			child.HandleMouseScroll (
 				int(buttonEvent.EventX),
 				int(buttonEvent.EventY),
 				float64(sum.x), float64(sum.y))

backends/x/window.go

@@ -76,26 +76,39 @@ func (backend *Backend) NewWindow (
 }
 
 func (window *Window) Adopt (child tomo.Element) {
+	// disown previous child
 	if window.child != nil {
-		window.child.SetParentHooks (tomo.ParentHooks { })
+		window.child.OnDamage(nil)
-		if previousChild, ok := window.child.(tomo.Selectable); ok {
+		window.child.OnMinimumSizeChange(nil)
-			if previousChild.Selected() {
+	}
-				previousChild.HandleDeselection()
+	if previousChild, ok := window.child.(tomo.Flexible); ok {
-			}
+		previousChild.OnFlexibleHeightChange(nil)
+	}
+	if previousChild, ok := window.child.(tomo.Selectable); ok {
+		previousChild.OnSelectionRequest(nil)
+		previousChild.OnSelectionMotionRequest(nil)
+		if previousChild.Selected() {
+			previousChild.HandleDeselection()
 		}
 	}
+	
+	// adopt new child
 	window.child = child
-	if child != nil {
+	if newChild, ok := child.(tomo.Flexible); ok {
-		child.SetParentHooks (tomo.ParentHooks {
+		newChild.OnFlexibleHeightChange(window.resizeChildToFit)
-			Draw: window.childDrawCallback,
+	}
-			MinimumSizeChange: window.childMinimumSizeChangeCallback,
+	if newChild, ok := child.(tomo.Selectable); ok {
-			FlexibleHeightChange: window.resizeChildToFit,
+		newChild.OnSelectionRequest(window.childSelectionRequestCallback)
-			SelectionRequest: window.childSelectionRequestCallback,
+	}
-		})
+	if child != nil {
-		
+		child.OnDamage(window.childDrawCallback)
-		window.resizeChildToFit()
+		child.OnMinimumSizeChange (func () {
+			window.childMinimumSizeChangeCallback (
+				child.MinimumSize())
+		})
+		window.resizeChildToFit()
+		window.childMinimumSizeChangeCallback(child.MinimumSize())
 	}
-	window.childMinimumSizeChangeCallback(child.MinimumSize())
 }
 
 func (window *Window) Child () (child tomo.Element) {
@@ -204,7 +217,7 @@ func (window *Window) redrawChildEntirely () {
 func (window *Window) resizeChildToFit () {
 	window.skipChildDrawCallback = true
 	if child, ok := window.child.(tomo.Flexible); ok {
-		minimumHeight := child.MinimumHeightFor(window.metrics.width)
+		minimumHeight := child.FlexibleHeightFor(window.metrics.width)
 		minimumWidth, _ := child.MinimumSize()
 		
 		icccm.WmNormalHintsSet (

element.go

@@ -2,96 +2,6 @@ package tomo
 
 import "image"
 
-// 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. 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.
-	Draw func (region Canvas)
-
-	// MinimumSizeChange is called when the child element's minimum width
-	// and/or height changes. When this function is called, the element will
-	// have already been resized and there is no need to send it a resize
-	// event.
-	MinimumSizeChange func (width, height int)
-
-	// FlexibleHeightChange is called when the parameters affecting the
-	// element's felxible height have changed.
-	FlexibleHeightChange func ()
-
-	// ContentBoundsChange is called by scrollable elements when the
-	// element's content bounds have changed. When this function is called,
-	// the element will have already done any drawing necessary. This is
-	// only intended for updating things like scrollbar positions.
-	ContentBoundsChange func ()
-	
-	// SelectionRequest is called when the child element element wants
-	// itself to be selected. If the parent element chooses to grant the
-	// 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.
-func (hooks ParentHooks) RunDraw (region Canvas) {
-	if hooks.Draw != nil {
-		hooks.Draw(region)
-	}
-}
-
-// RunMinimumSizeChange runs the MinimumSizeChange hook if it is not nil. If it
-// is nil, it does nothing.
-func (hooks ParentHooks) RunMinimumSizeChange (width, height int) {
-	if hooks.MinimumSizeChange != nil {
-		hooks.MinimumSizeChange(width, height)
-	}
-}
-
-// RunFlexibleHeightChange runs the ExpandingHeightChange hook if it is not
-// nil. If it is nil, it does nothing.
-func (hooks ParentHooks) RunFlexibleHeightChange () {
-	if hooks.FlexibleHeightChange != nil {
-		hooks.FlexibleHeightChange()
-	}
-}
-
-// RunSelectionRequest runs the SelectionRequest hook if it is not nil. If it is
-// nil, it does nothing.
-func (hooks ParentHooks) RunSelectionRequest () (granted bool) {
-	if hooks.SelectionRequest != nil {
-		granted = hooks.SelectionRequest()
-	}
-	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
-}
-
-// RunContentBoundsChange runs the ContentBoundsChange hook if it is not nil. If
-// it is nil, it does nothing.
-func (hooks ParentHooks) RunContentBoundsChange () {
-	if hooks.ContentBoundsChange != nil {
-		hooks.ContentBoundsChange()
-	}
-}
-
 // Element represents a basic on-screen object.
 type Element interface {
 	// Element must implement the Canvas interface. Elements should start
@@ -109,11 +19,13 @@ type Element interface {
 	// element's parent.
 	Resize (width, height int)
 
-	// SetParentHooks gives the element callbacks that let it send
+	// OnDamage sets a function to be called when an area of the element is
-	// information to its parent element without it knowing anything about
+	// drawn on and should be pushed to the screen.
-	// the parent element or containing any reference to it. When a parent
+	OnDamage (callback func (region Canvas))
-	// element adopts a child element, it must set these callbacks.
+
-	SetParentHooks (callbacks ParentHooks)
+	// OnMinimumSizeChange sets a function to be called when the element's
+	// minimum size is changed.
+	OnMinimumSizeChange (callback func ())
 }
 
 // SelectionDirection represents a keyboard navigation direction.
@@ -156,6 +68,18 @@ type Selectable interface {
 	// HandleDeselection causes this element to mark itself and all of its
 	// children as deselected.
 	HandleDeselection ()
+
+	// OnSelectionRequest sets a function to be called when this element
+	// wants its parent element to select it. Parent elements should return
+	// true if the request was granted, and false if it was not.
+	OnSelectionRequest (func () (granted bool))
+
+	// OnSelectionMotionRequest sets a function to be called when this
+	// element wants its parent element to select the element behind or in
+	// front of it, depending on the specified direction. Parent elements
+	// should return true if the request was granted, and false if it was
+	// not.
+	OnSelectionMotionRequest (func (SelectionDirection) (granted bool))
 }
 
 // KeyboardTarget represents an element that can receive keyboard input.
@@ -196,7 +120,7 @@ type MouseTarget interface {
 
 	// HandleScroll is called when the mouse is scrolled. The X and Y
 	// direction of the scroll event are passed as deltaX and deltaY.
-	HandleScroll (x, y int, deltaX, deltaY float64)
+	HandleMouseScroll (x, y int, deltaX, deltaY float64)
 }
 
 // Flexible represents an element who's preferred minimum height can change in
@@ -204,10 +128,10 @@ type MouseTarget interface {
 type Flexible interface {
 	Element
 
-	// HeightForWidth returns what the element's minimum height would be if
+	// FlexibleHeightFor returns what the element's minimum height would be
-	// resized to a specified width. This does not actually alter the state
+	// if resized to a specified width. This does not actually alter the
-	// of the element in any way, but it may perform significant work, so it
+	// state of the element in any way, but it may perform significant work,
-	// should be called sparingly.
+	// so it should be called sparingly.
 	//
 	// It is reccomended that parent containers check for this interface and
 	// take this method's value into account in order to support things like
@@ -217,7 +141,11 @@ type Flexible interface {
 	//
 	// It is important to note that if a parent container checks for
 	// flexible chilren, it itself will likely need to be flexible.
-	MinimumHeightFor (width int) (height int)
+	FlexibleHeightFor (width int) (height int)
+
+	// OnFlexibleHeightChange sets a function to be called when the
+	// parameters affecting this element's flexible height are changed.
+	OnFlexibleHeightChange (callback func ())
 }
 
 // Scrollable represents an element that can be scrolled. It acts as a viewport
@@ -238,4 +166,8 @@ type Scrollable interface {
 
 	// ScrollAxes returns the supported axes for scrolling.
 	ScrollAxes () (horizontal, vertical bool)
+
+	// OnScrollBoundsChange sets a function to be called when the element's
+	// ScrollContentBounds or ScrollViewportBounds are changed.
+	OnScrollBoundsChange (callback func ())
 }

elements/basic/button.go

@@ -14,10 +14,13 @@ type Button struct {
 	pressed  bool
 	enabled  bool
 	selected bool
-	onClick func ()
 
 	text   string
 	drawer artist.TextDrawer
+	
+	onClick func ()
+	onSelectionRequest func () (granted bool)
+	onSelectionMotionRequest func (tomo.SelectionDirection) (granted bool)
 }
 
 // NewButton creates a new button with the specified label text.
@@ -41,7 +44,7 @@ func (element *Button) HandleMouseDown (x, y int, button tomo.Button) {
 	element.pressed = true
 	if element.core.HasImage() {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
@@ -50,7 +53,7 @@ func (element *Button) HandleMouseUp (x, y int, button tomo.Button) {
 	element.pressed = false
 	if element.core.HasImage() {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 
 	within := image.Point { x, y }.
@@ -63,7 +66,7 @@ func (element *Button) HandleMouseUp (x, y int, button tomo.Button) {
 }
 
 func (element *Button) HandleMouseMove (x, y int) { }
-func (element *Button) HandleScroll (x, y int, deltaX, deltaY float64) { }
+func (element *Button) HandleMouseScroll (x, y int, deltaX, deltaY float64) { }
 
 func (element *Button) HandleKeyDown (
 	key tomo.Key,
@@ -75,7 +78,7 @@ func (element *Button) HandleKeyDown (
 		element.pressed = true
 		if element.core.HasImage() {
 			element.draw()
-			element.core.PushAll()
+			element.core.DamageAll()
 		}
 	}
 }
@@ -85,7 +88,7 @@ func (element *Button) HandleKeyUp(key tomo.Key, modifiers tomo.Modifiers) {
 		element.pressed = false
 		if element.core.HasImage() {
 			element.draw()
-			element.core.PushAll()
+			element.core.DamageAll()
 		}
 		if !element.enabled { return }
 		if element.onClick != nil {
@@ -100,7 +103,9 @@ func (element *Button) Selected () (selected bool) {
 
 func (element *Button) Select () {
 	if !element.enabled { return }
-	element.core.RequestSelection()
+	if element.onSelectionRequest != nil {
+		element.onSelectionRequest()
+	}
 }
 
 func (element *Button) HandleSelection (
@@ -117,7 +122,7 @@ func (element *Button) HandleSelection (
 	element.selected = true
 	if element.core.HasImage() {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 	return true
 }
@@ -126,10 +131,20 @@ func (element *Button) HandleDeselection () {
 	element.selected = false
 	if element.core.HasImage() {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
+func (element *Button) OnSelectionRequest (callback func () (granted bool)) {
+	element.onSelectionRequest = callback
+}
+
+func (element *Button) OnSelectionMotionRequest (
+	callback func (direction tomo.SelectionDirection) (granted bool),
+) {
+	element.onSelectionMotionRequest = callback
+}
+
 // OnClick sets the function to be called when the button is clicked.
 func (element *Button) OnClick (callback func ()) {
 	element.onClick = callback
@@ -141,7 +156,7 @@ func (element *Button) SetEnabled (enabled bool) {
 	element.enabled = enabled
 	if element.core.HasImage () {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
@@ -157,7 +172,7 @@ func (element *Button) SetText (text string) {
 		theme.Padding() * 2 + textBounds.Dy())
 	if element.core.HasImage () {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 

elements/basic/checkbox.go

@@ -15,10 +15,13 @@ type Checkbox struct {
 	checked  bool
 	enabled  bool
 	selected bool
-	onClick func ()
 
 	text   string
 	drawer artist.TextDrawer
+	
+	onClick func ()
+	onSelectionRequest func () (granted bool)
+	onSelectionMotionRequest func (tomo.SelectionDirection) (granted bool)
 }
 
 // NewCheckbox creates a new cbeckbox with the specified label text.
@@ -41,7 +44,7 @@ func (element *Checkbox) HandleMouseDown (x, y int, button tomo.Button) {
 	element.pressed = true
 	if element.core.HasImage() {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
@@ -57,7 +60,7 @@ func (element *Checkbox) HandleMouseUp (x, y int, button tomo.Button) {
 	
 	if element.core.HasImage() {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 	if within && element.onClick != nil {
 		element.onClick()
@@ -76,7 +79,7 @@ func (element *Checkbox) HandleKeyDown (
 		element.pressed = true
 		if element.core.HasImage() {
 			element.draw()
-			element.core.PushAll()
+			element.core.DamageAll()
 		}
 	}
 }
@@ -87,7 +90,7 @@ func (element *Checkbox) HandleKeyUp (key tomo.Key, modifiers tomo.Modifiers) {
 		element.checked = !element.checked
 		if element.core.HasImage() {
 			element.draw()
-			element.core.PushAll()
+			element.core.DamageAll()
 		}
 		if element.onClick != nil {
 			element.onClick()
@@ -102,7 +105,10 @@ func (element *Checkbox) Selected () (selected bool) {
 
 // Select requests that this element be selected.
 func (element *Checkbox) Select () {
-	element.core.RequestSelection()
+	if !element.enabled { return }
+	if element.onSelectionRequest != nil {
+		element.onSelectionRequest()
+	}
 }
 
 func (element *Checkbox) HandleSelection (
@@ -119,7 +125,7 @@ func (element *Checkbox) HandleSelection (
 	element.selected = true
 	if element.core.HasImage() {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 	return true
 }
@@ -128,10 +134,20 @@ func (element *Checkbox) HandleDeselection () {
 	element.selected = false
 	if element.core.HasImage() {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
+func (element *Checkbox) OnSelectionRequest (callback func () (granted bool)) {
+	element.onSelectionRequest = callback
+}
+
+func (element *Checkbox) OnSelectionMotionRequest (
+	callback func (direction tomo.SelectionDirection) (granted bool),
+) {
+	element.onSelectionMotionRequest = callback
+}
+
 // OnClick sets the function to be called when the checkbox is toggled.
 func (element *Checkbox) OnClick (callback func ()) {
 	element.onClick = callback
@@ -148,7 +164,7 @@ func (element *Checkbox) SetEnabled (enabled bool) {
 	element.enabled = enabled
 	if element.core.HasImage () {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
@@ -164,7 +180,7 @@ func (element *Checkbox) SetText (text string) {
 		textBounds.Dy())
 	if element.core.HasImage () {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 

elements/basic/container.go

@@ -19,6 +19,10 @@ type Container struct {
 	selected   bool
 	selectable bool
 	flexible   bool
+	
+	onSelectionRequest func () (granted bool)
+	onSelectionMotionRequest func (tomo.SelectionDirection) (granted bool)
+	onFlexibleHeightChange func ()
 }
 
 // NewContainer creates a new container.
@@ -35,7 +39,7 @@ func (element *Container) SetLayout (layout tomo.Layout) {
 	if element.core.HasImage() {
 		element.recalculate()
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
@@ -43,38 +47,38 @@ func (element *Container) SetLayout (layout tomo.Layout) {
 // the element will expand (instead of contract to its minimum size), in
 // whatever way is defined by the current layout.
 func (element *Container) Adopt (child tomo.Element, expand bool) {
-	child.SetParentHooks (tomo.ParentHooks {
+	// set event handlers
-		Draw: func (region tomo.Canvas) {
+	child.OnDamage (func (region tomo.Canvas) {
-			element.drawChildRegion(child, region)
+		element.drawChildRegion(child, region)
-		},
-		MinimumSizeChange: func (int, int) {
-			element.updateMinimumSize()
-		},
-		FlexibleHeightChange: element.updateMinimumSize,
-		SelectionRequest: func () (granted bool) {
-			child, selectable := child.(tomo.Selectable)
-			if !selectable { return }
-			return element.childSelectionRequestCallback(child)
-		},
-		SelectionMotionRequest: func (
-			direction tomo.SelectionDirection,
-		) (
-			granted bool,
-		) {
-			return element.core.RequestSelectionMotion(direction)
-		},
 	})
+	child.OnMinimumSizeChange(element.updateMinimumSize)
+	if child0, ok := child.(tomo.Flexible); ok {
+		child0.OnFlexibleHeightChange(element.updateMinimumSize)
+	}
+	if child0, ok := child.(tomo.Selectable); ok {
+		child0.OnSelectionRequest (func () (granted bool) {
+			return element.childSelectionRequestCallback(child0)
+		})
+		child0.OnSelectionMotionRequest (
+			func (direction tomo.SelectionDirection) (granted bool) {
+				if element.onSelectionMotionRequest == nil { return }
+				return element.onSelectionMotionRequest(direction)
+			})
+	}
+
+	// add child
 	element.children = append (element.children, tomo.LayoutEntry {
 		Element: child,
 		Expand:  expand,
 	})
 
+	// refresh stale data
 	element.updateMinimumSize()
 	element.reflectChildProperties()
 	if element.core.HasImage() && !element.warping {
 		element.recalculate()
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
@@ -97,7 +101,7 @@ func (element *Container) Warp (callback func ()) {
 	if element.core.HasImage() {
 		element.recalculate()
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
@@ -106,7 +110,7 @@ func (element *Container) Warp (callback func ()) {
 func (element *Container) Disown (child tomo.Element) {
 	for index, entry := range element.children {
 		if entry.Element == child {
-			entry.SetParentHooks(tomo.ParentHooks { })
+			element.clearChildEventHandlers(entry.Element)
 			element.children = append (
 				element.children[:index],
 				element.children[index + 1:]...)
@@ -119,7 +123,22 @@ func (element *Container) Disown (child tomo.Element) {
 	if element.core.HasImage() && !element.warping {
 		element.recalculate()
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
+	}
+}
+
+func (element *Container) clearChildEventHandlers (child tomo.Element) {
+	child.OnDamage(nil)
+	child.OnMinimumSizeChange(nil)
+	if child0, ok := child.(tomo.Selectable); ok {
+		child0.OnSelectionRequest(nil)
+		child0.OnSelectionMotionRequest(nil)
+		if child0.Selected() {
+			child0.HandleDeselection()
+		}
+	}
+	if child0, ok := child.(tomo.Flexible); ok {
+		child0.OnFlexibleHeightChange(nil)
 	}
 }
 
@@ -132,7 +151,7 @@ func (element *Container) DisownAll () {
 	if element.core.HasImage() && !element.warping {
 		element.recalculate()
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
@@ -209,11 +228,11 @@ func (element *Container) HandleMouseMove (x, y int) {
 	}
 }
 
-func (element *Container) HandleScroll (x, y int, deltaX, deltaY float64) {
+func (element *Container) HandleMouseScroll (x, y int, deltaX, deltaY float64) {
 	child, handlesMouse := element.ChildAt(image.Pt(x, y)).(tomo.MouseTarget)
 	if !handlesMouse { return }
 	childPosition := element.childPosition(child)
-	child.HandleScroll(x - childPosition.X, y - childPosition.Y, deltaX, deltaY)
+	child.HandleMouseScroll(x - childPosition.X, y - childPosition.Y, deltaX, deltaY)
 }
 
 func (element *Container) HandleKeyDown (
@@ -245,7 +264,9 @@ func (element *Container) Selected () (selected bool) {
 }
 
 func (element *Container) Select () {
-	element.core.RequestSelection()
+	if element.onSelectionRequest != nil {
+		element.onSelectionRequest()
+	}
 }
 
 func (element *Container) HandleSelection (direction tomo.SelectionDirection) (ok bool) {
@@ -300,8 +321,12 @@ func (element *Container) HandleSelection (direction tomo.SelectionDirection) (o
 	return false
 }
 
-func (element *Container) MinimumHeightFor (width int) (height int) {
+func (element *Container) FlexibleHeightFor (width int) (height int) {
-	return element.layout.MinimumHeightFor(element.children, width)
+	return element.layout.FlexibleHeightFor(element.children, width)
+}
+
+func (element *Container) OnFlexibleHeightChange (callback func ()) {
+	element.onFlexibleHeightChange = callback
 }
 
 func (element *Container) HandleDeselection () {
@@ -312,6 +337,16 @@ func (element *Container) HandleDeselection () {
 	})
 }
 
+func (element *Container) OnSelectionRequest (callback func () (granted bool)) {
+	element.onSelectionRequest = callback
+}
+
+func (element *Container) OnSelectionMotionRequest (
+	callback func (direction tomo.SelectionDirection) (granted bool),
+) {
+	element.onSelectionMotionRequest = callback
+}
+
 func (element *Container) forSelected (callback func (child tomo.Selectable) bool) {
 	for _, entry := range element.children {
 		child, selectable := entry.Element.(tomo.Selectable)
@@ -379,7 +414,7 @@ func (element *Container) childSelectionRequestCallback (
 ) (
 	granted bool,
 ) {
-	if element.core.RequestSelection() {
+	if element.onSelectionRequest != nil && element.onSelectionRequest() {
 		element.forSelected (func (child tomo.Selectable) bool {
 			child.HandleDeselection()
 			return true
@@ -394,7 +429,7 @@ func (element *Container) childSelectionRequestCallback (
 func (element *Container) updateMinimumSize () {
 	width, height := element.layout.MinimumSize(element.children)
 	if element.flexible {
-		height = element.layout.MinimumHeightFor(element.children, width)
+		height = element.layout.FlexibleHeightFor(element.children, width)
 	}
 	element.core.SetMinimumSize(width, height)
 }
@@ -422,7 +457,7 @@ func (element *Container) drawChildRegion (child tomo.Element, region tomo.Canva
 	for _, entry := range element.children {
 		if entry.Element == child {
 			artist.Paste(element.core, region, entry.Position)
-			element.core.PushRegion (
+			element.core.DamageRegion (
 				region.Bounds().Add(entry.Position))
 			break
 		}

elements/basic/label.go

@@ -13,6 +13,8 @@ type Label struct {
 	wrap   bool
 	text   string
 	drawer artist.TextDrawer
+	
+	onFlexibleHeightChange func ()
 }
 
 // NewLabel creates a new label. If wrap is set to true, the text inside will be
@@ -38,9 +40,9 @@ func (element *Label) Resize (width, height int) {
 	return
 }
 
-// MinimumHeightFor returns the reccomended height for this element based on the
+// FlexibleHeightFor returns the reccomended height for this element based on
-// given width in order to allow the text to wrap properly.
+// the given width in order to allow the text to wrap properly.
-func (element *Label) MinimumHeightFor (width int) (height int) {
+func (element *Label) FlexibleHeightFor (width int) (height int) {
 	if element.wrap {
 		return element.drawer.ReccomendedHeightFor(width)
 	} else {
@@ -49,6 +51,12 @@ func (element *Label) MinimumHeightFor (width int) (height int) {
 	}
 }
 
+// OnFlexibleHeightChange sets a function to be called when the parameters
+// affecting this element's flexible height are changed.
+func (element *Label) OnFlexibleHeightChange (callback func ()) {
+	element.onFlexibleHeightChange = callback
+}
+
 // SetText sets the label's text.
 func (element *Label) SetText (text string) {
 	if element.text == text { return }
@@ -59,7 +67,7 @@ func (element *Label) SetText (text string) {
 	
 	if element.core.HasImage () {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
@@ -78,7 +86,7 @@ func (element *Label) SetWrap (wrap bool) {
 	
 	if element.core.HasImage () {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
@@ -88,7 +96,9 @@ func (element *Label) updateMinimumSize () {
 		if em < 1 { em = theme.Padding() }
 		element.core.SetMinimumSize (
 			em, element.drawer.LineHeight().Round())
-		element.core.NotifyFlexibleHeightChange()
+		if element.onFlexibleHeightChange != nil {
+			element.onFlexibleHeightChange()
+		}
 	} else {
 		bounds := element.drawer.LayoutBounds()
 		element.core.SetMinimumSize(bounds.Dx(), bounds.Dy())

elements/basic/progressbar.go

@@ -34,7 +34,7 @@ func (element *ProgressBar) SetProgress (progress float64) {
 	element.progress = progress
 	if element.core.HasImage() {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 

elements/basic/scrollcontainer.go

@@ -23,6 +23,9 @@ type ScrollContainer struct {
 		enabled bool
 		bounds image.Rectangle
 	}
+
+	onSelectionRequest func () (granted bool)
+	onSelectionMotionRequest func (tomo.SelectionDirection) (granted bool)
 }
 
 // NewScrollContainer creates a new scroll container with the specified scroll
@@ -52,23 +55,20 @@ func (element *ScrollContainer) Resize (width, height int) {
 func (element *ScrollContainer) Adopt (child tomo.Scrollable) {
 	// disown previous child if it exists
 	if element.child != nil {
-		element.child.SetParentHooks (tomo.ParentHooks { })
+		element.clearChildEventHandlers(child)
-		if previousChild, ok := element.child.(tomo.Selectable); ok {
-			if previousChild.Selected() {
-				previousChild.HandleDeselection()
-			}
-		}
 	}
 
 	// adopt new child
 	element.child = child
 	if child != nil {
-		child.SetParentHooks (tomo.ParentHooks {
+		child.OnDamage(element.childDamageCallback)
-			// Draw: window.childDrawCallback,
+		child.OnMinimumSizeChange(element.updateMinimumSize)
-			// MinimumSizeChange: window.childMinimumSizeChangeCallback,
+		if newChild, ok := child.(tomo.Selectable); ok {
-			// FlexibleHeightChange: window.resizeChildToFit,
+			newChild.OnSelectionRequest (
-			// SelectionRequest: window.childSelectionRequestCallback,
+				element.childSelectionRequestCallback)
-		})
+			newChild.OnSelectionMotionRequest (
+				element.childSelectionMotionRequestCallback)
+		}
 
 		// TODO: somehow inform the core that we do not in fact want to
 		// redraw the element.
@@ -84,6 +84,104 @@ func (element *ScrollContainer) Adopt (child tomo.Scrollable) {
 	}
 }
 
+func (element *ScrollContainer) HandleKeyDown (
+	key tomo.Key,
+	modifiers tomo.Modifiers,
+	repeated bool,
+) {
+	if child, ok := element.child.(tomo.KeyboardTarget); ok {
+		child.HandleKeyDown(key, modifiers, repeated)
+	}
+}
+
+func (element *ScrollContainer) HandleKeyUp (key tomo.Key, modifiers tomo.Modifiers) {
+	if child, ok := element.child.(tomo.KeyboardTarget); ok {
+		child.HandleKeyUp(key, modifiers)
+	}
+}
+
+func (element *ScrollContainer) Selected () (selected bool) {
+	return element.selected
+}
+
+func (element *ScrollContainer) Select () {
+	if element.onSelectionRequest != nil {
+		element.onSelectionRequest()
+	}
+}
+
+func (element *ScrollContainer) HandleSelection (
+	direction tomo.SelectionDirection,
+) (
+	accepted bool,
+) {
+	if child, ok := element.child.(tomo.Selectable); ok {
+		element.selected = true
+		return child.HandleSelection(direction)
+	} else {
+		element.selected = false
+		return false
+	}
+}
+
+func (element *ScrollContainer) HandleDeselection () {
+	if child, ok := element.child.(tomo.Selectable); ok {
+		child.HandleDeselection()
+	}
+	element.selected = false
+}
+
+func (element *ScrollContainer) OnSelectionRequest (callback func () (granted bool)) {
+	element.onSelectionRequest = callback
+}
+
+func (element *ScrollContainer) OnSelectionMotionRequest (
+	callback func (direction tomo.SelectionDirection) (granted bool),
+) {
+	element.onSelectionMotionRequest = callback
+}
+
+func (element *ScrollContainer) childDamageCallback (region tomo.Canvas) {
+	element.core.DamageRegion(artist.Paste(element, region, image.Point { }))
+}
+
+func (element *ScrollContainer) childSelectionRequestCallback () (granted bool) {
+	child, ok := element.child.(tomo.Selectable)
+	if !ok { return false }
+	if element.onSelectionRequest != nil && element.onSelectionRequest() {
+		child.HandleSelection(tomo.SelectionDirectionNeutral)
+		return true
+	} else {
+		return false
+	}
+}
+
+func (element *ScrollContainer) childSelectionMotionRequestCallback (
+	direction tomo.SelectionDirection,
+) (
+	granted bool,
+) {
+	if element.onSelectionMotionRequest == nil {
+		 return
+	}
+	return element.onSelectionMotionRequest(direction)
+}
+
+func (element *ScrollContainer) clearChildEventHandlers (child tomo.Element) {
+	child.OnDamage(nil)
+	child.OnMinimumSizeChange(nil)
+	if child0, ok := child.(tomo.Selectable); ok {
+		child0.OnSelectionRequest(nil)
+		child0.OnSelectionMotionRequest(nil)
+		if child0.Selected() {
+			child0.HandleDeselection()
+		}
+	}
+	if child0, ok := child.(tomo.Flexible); ok {
+		child0.OnFlexibleHeightChange(nil)
+	}
+}
+
 func (element *ScrollContainer) recalculate () {
 	horizontal := &element.horizontal
 	vertical   := &element.vertical

elements/basic/spacer.go

@@ -34,7 +34,7 @@ func (element *Spacer) SetLine (line bool) {
 	element.line = line
 	if element.core.HasImage() {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 

elements/basic/textbox.go

@@ -25,6 +25,9 @@ type TextBox struct {
 	
 	onKeyDown func (tomo.Key, tomo.Modifiers, bool) (bool)
 	onChange  func ()
+	onSelectionRequest func () (granted bool)
+	onSelectionMotionRequest func (tomo.SelectionDirection) (granted bool)
+	onScrollBoundsChange func ()
 }
 
 // NewTextBox creates a new text box with the specified placeholder text, and
@@ -119,7 +122,7 @@ func (element *TextBox) HandleKeyDown (
 	
 	if altered && element.core.HasImage () {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
@@ -130,7 +133,9 @@ func (element *TextBox) Selected () (selected bool) {
 }
 
 func (element *TextBox) Select () {
-	element.core.RequestSelection()
+	if element.onSelectionRequest != nil {
+		element.onSelectionRequest()
+	}
 }
 
 func (element *TextBox) HandleSelection (
@@ -147,7 +152,7 @@ func (element *TextBox) HandleSelection (
 	element.selected = true
 	if element.core.HasImage() {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 	return true
 }
@@ -156,16 +161,26 @@ func (element *TextBox) HandleDeselection () {
 	element.selected = false
 	if element.core.HasImage() {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
+func (element *TextBox) OnSelectionRequest (callback func () (granted bool)) {
+	element.onSelectionRequest = callback
+}
+
+func (element *TextBox) OnSelectionMotionRequest (
+	callback func (direction tomo.SelectionDirection) (granted bool),
+) {
+	element.onSelectionMotionRequest = callback
+}
+
 func (element *TextBox) SetEnabled (enabled bool) {
 	if element.enabled == enabled { return }
 	element.enabled = enabled
 	if element.core.HasImage () {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
@@ -178,7 +193,7 @@ func (element *TextBox) SetPlaceholder (placeholder string) {
 	element.updateMinimumSize()
 	if element.core.HasImage () {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
@@ -195,7 +210,7 @@ func (element *TextBox) SetValue (text string) {
 	
 	if element.core.HasImage () {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
 	}
 }
 
@@ -246,9 +261,11 @@ func (element *TextBox) ScrollTo (position image.Point) {
 
 	if element.core.HasImage () {
 		element.draw()
-		element.core.PushAll()
+		element.core.DamageAll()
+	}
+	if element.onScrollBoundsChange != nil {
+		element.onScrollBoundsChange()
 	}
-	element.core.NotifyContentBoundsChange()
 }
 
 // ScrollAxes returns the supported axes for scrolling.
@@ -256,6 +273,10 @@ func (element *TextBox) ScrollAxes () (horizontal, vertical bool) {
 	return true, false
 }
 
+func (element *TextBox) OnScrollBoundsChange (callback func ()) {
+	element.onScrollBoundsChange = callback
+}
+
 func (element *TextBox) updateMinimumSize () {
 	textBounds := element.placeholderDrawer.LayoutBounds()
 	element.core.SetMinimumSize (
@@ -286,7 +307,9 @@ func (element *TextBox) scrollToCursor () {
 		element.scroll -= minX - cursorPosition.X
 		if element.scroll < 0 { element.scroll = 0 }
 	}
-	element.core.NotifyContentBoundsChange()
+	if element.onScrollBoundsChange != nil {
+		element.onScrollBoundsChange()
+	}
 }
 
 func (element *TextBox) draw () {

elements/core/core.go

@@ -17,7 +17,9 @@ type Core struct {
 
 	selectable bool
 	selected   bool
-	hooks tomo.ParentHooks
+
+	onMinimumSizeChange func ()
+	onDamage func (region tomo.Canvas)
 }
 
 // NewCore creates a new element core and its corresponding control.
@@ -58,10 +60,16 @@ func (core *Core) MinimumSize () (width, height int) {
 	return core.metrics.minimumWidth, core.metrics.minimumHeight
 }
 
-// SetParentHooks fulfils the tomo.Element interface. This should not need to be
+// OnDamage fulfils the tomo.Element interface. This should not need to be
 // overridden.
-func (core *Core) SetParentHooks (hooks tomo.ParentHooks) {
+func (core *Core) OnDamage (callback func (region tomo.Canvas)) {
-	core.hooks = hooks
+	core.onDamage = callback
+}
+
+// OnMinimumSizeChange fulfils the tomo.Element interface. This should not need
+// to be overridden.
+func (core *Core) OnMinimumSizeChange (callback func ()) {
+	core.onMinimumSizeChange = callback
 }
 
 // CoreControl is a struct that can exert control over a Core struct. It can be
@@ -73,41 +81,24 @@ type CoreControl struct {
 	core *Core
 }
 
-// RequestSelection requests that the element's parent send it a selection
-// event. If the request was granted, it returns true. If it was denied, it
-// returns false.
-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) {
 	return !control.Bounds().Empty()
 }
 
-// PushRegion pushes the selected region of pixels to the parent element. This
+// DamageRegion pushes the selected region of pixels to the parent element. This
 // does not need to be called when responding to a resize event.
-func (control CoreControl) PushRegion (bounds image.Rectangle) {
+func (control CoreControl) DamageRegion (bounds image.Rectangle) {
-	control.core.hooks.RunDraw(tomo.Cut(control, bounds))
+	if control.core.onDamage != nil {
+		control.core.onDamage(tomo.Cut(control, bounds))
+	}
 }
 
-// PushAll pushes all pixels to the parent element. This does not need to be
+// DamageAll pushes all pixels to the parent element. This does not need to be
 // called when responding to a resize event.
-func (control CoreControl) PushAll () {
+func (control CoreControl) DamageAll () {
-	control.PushRegion(control.Bounds())
+	control.DamageRegion(control.Bounds())
 }
 
 // AllocateCanvas resizes the canvas, constraining the width and height so that
@@ -128,7 +119,9 @@ func (control CoreControl) SetMinimumSize (width, height int) {
 
 	core.metrics.minimumWidth  = width
 	core.metrics.minimumHeight = height
-	core.hooks.RunMinimumSizeChange(width, height)
+	if control.core.onMinimumSizeChange != nil {
+		control.core.onMinimumSizeChange()
+	}
 
 	// if there is an image buffer, and the current size is less
 	// than this new minimum size, send core.parent a resize event.
@@ -143,18 +136,6 @@ func (control CoreControl) SetMinimumSize (width, height int) {
 	}
 }
 
-// NotifyFlexibleHeightChange notifies the parent element that this element's
-// flexible height has changed.
-func (control CoreControl) NotifyFlexibleHeightChange () {
-	control.core.hooks.RunFlexibleHeightChange()
-}
-
-// NotifyContentBoundsChange notifies the parent element that this element's
-// inner content bounds or scroll position have changed.
-func (control CoreControl) NotifyContentBoundsChange () {
-	control.core.hooks.RunContentBoundsChange()
-}
-
 // ConstrainSize contstrains the specified width and height to the minimum width
 // and height, and returns wether or not anything ended up being constrained.
 func (control CoreControl) ConstrainSize (

elements/testing/mouse.go

@@ -54,7 +54,7 @@ func (element *Mouse) HandleMouseDown (x, y int, button tomo.Button) {
 func (element *Mouse) HandleMouseUp (x, y int, button tomo.Button) {
 	element.drawing = false
 	mousePos := image.Pt(x, y)
-	element.core.PushRegion (artist.Line (
+	element.core.DamageRegion (artist.Line (
 		element.core, element.color, 1,
 		element.lastMousePos, mousePos))
 	element.lastMousePos = mousePos
@@ -63,10 +63,10 @@ func (element *Mouse) HandleMouseUp (x, y int, button tomo.Button) {
 func (element *Mouse) HandleMouseMove (x, y int) {
 	if !element.drawing { return }
 	mousePos := image.Pt(x, y)
-	element.core.PushRegion (artist.Line (
+	element.core.DamageRegion (artist.Line (
 		element.core, element.color, 1,
 		element.lastMousePos, mousePos))
 	element.lastMousePos = mousePos
 }
 
-func (element *Mouse) HandleScroll (x, y int, deltaX, deltaY float64) { }
+func (element *Mouse) HandleMouseScroll (x, y int, deltaX, deltaY float64) { }

layout.go

@@ -23,8 +23,8 @@ type Layout interface {
 	// needs to properly arrange the given slice of layout entries.
 	MinimumSize (entries []LayoutEntry) (width, height int)
 
-	// MinimumHeightFor Returns the minimum height the layout needs to lay
+	// FlexibleHeightFor Returns the minimum height the layout needs to lay
 	// out the specified elements at the given width, taking into account
 	// flexible elements.
-	MinimumHeightFor (entries []LayoutEntry, squeeze int) (height int)
+	FlexibleHeightFor (entries []LayoutEntry, squeeze int) (height int)
 }

layouts/dialog.go

@@ -134,7 +134,9 @@ func (layout Dialog) MinimumSize (
 	return
 }
 
-func (layout Dialog) MinimumHeightFor (
+// FlexibleHeightFor Returns the minimum height the layout needs to lay out the
+// specified elements at the given width, taking into account flexible elements.
+func (layout Dialog) FlexibleHeightFor (
 	entries []tomo.LayoutEntry,
 	width int,
 ) (
@@ -147,7 +149,7 @@ func (layout Dialog) MinimumHeightFor (
 	if len(entries) > 0 {
 		mainChildHeight := 0
 		if child, flexible := entries[0].Element.(tomo.Flexible); flexible {
-			mainChildHeight = child.MinimumHeightFor(width)
+			mainChildHeight = child.FlexibleHeightFor(width)
 		} else {
 			_, mainChildHeight = entries[0].MinimumSize()
 		}

layouts/horizontal.go

@@ -75,7 +75,9 @@ func (layout Horizontal) MinimumSize (
 	return
 }
 
-func (layout Horizontal) MinimumHeightFor (
+// FlexibleHeightFor Returns the minimum height the layout needs to lay out the
+// specified elements at the given width, taking into account flexible elements.
+func (layout Horizontal) FlexibleHeightFor (
 	entries []tomo.LayoutEntry,
 	width int,
 ) (
@@ -100,7 +102,7 @@ func (layout Horizontal) MinimumHeightFor (
 			entryWidth = expandingElementWidth
 		}
 		if child, flexible := entry.Element.(tomo.Flexible); flexible {
-			entryHeight = child.MinimumHeightFor(entryWidth)
+			entryHeight = child.FlexibleHeightFor(entryWidth)
 		}
 		if entryHeight > height { height = entryHeight }
 		

layouts/vertical.go

@@ -32,7 +32,7 @@ func (layout Vertical) Arrange (entries []tomo.LayoutEntry, width, height int) {
 		var entryMinHeight int
 
 		if child, flexible := entry.Element.(tomo.Flexible); flexible {
-			entryMinHeight = child.MinimumHeightFor(width)
+			entryMinHeight = child.FlexibleHeightFor(width)
 		} else {
 			_, entryMinHeight = entry.MinimumSize()
 		}
@@ -102,9 +102,9 @@ func (layout Vertical) MinimumSize (
 	return
 }
 
-// MinimumHeightFor Returns the minimum height the layout needs to lay out the
+// FlexibleHeightFor Returns the minimum height the layout needs to lay out the
 // specified elements at the given width, taking into account flexible elements.
-func (layout Vertical) MinimumHeightFor (
+func (layout Vertical) FlexibleHeightFor (
 	entries []tomo.LayoutEntry,
 	width int,
 ) (
@@ -118,7 +118,7 @@ func (layout Vertical) MinimumHeightFor (
 	for index, entry := range entries {
 		child, flexible := entry.Element.(tomo.Flexible)
 		if flexible {
-			height += child.MinimumHeightFor(width)
+			height += child.FlexibleHeightFor(width)
 		} else {
 			_, entryHeight := entry.MinimumSize()
 			height += entryHeight