Re-added OnScrollBoundsChange methods because they are useful

elements/basic/documentContainer.go

@@ -21,6 +21,8 @@ type DocumentContainer struct {
 	
 	config config.Wrapped
 	theme  theme.Wrapped
+
+	onScrollBoundsChange func ()
 }
 
 // NewDocumentContainer creates a new document container.
@@ -255,6 +257,12 @@ func (element *DocumentContainer) ScrollTo (position image.Point) {
 	}
 }
 
+// OnScrollBoundsChange sets a function to be called when the element's viewport
+// bounds, content bounds, or scroll axes change.
+func (element *DocumentContainer) OnScrollBoundsChange (callback func ()) {
+	element.onScrollBoundsChange = callback
+}
+
 func (element *DocumentContainer) maxScrollHeight () (height int) {
 	padding := element.theme.Padding(theme.PatternSunken)
 	viewportHeight := element.Bounds().Dy() - padding.Vertical()

elements/basic/list.go

@@ -31,6 +31,7 @@ type List struct {
 	theme  theme.Wrapped
 	
 	onNoEntrySelected    func ()
+	onScrollBoundsChange func ()
 }
 
 // NewList creates a new list element with the specified entries.
@@ -240,6 +241,12 @@ func (element *List) OnNoEntrySelected (callback func ()) {
 	element.onNoEntrySelected = callback
 }
 
+// OnScrollBoundsChange sets a function to be called when the element's viewport
+// bounds, content bounds, or scroll axes change.
+func (element *List) OnScrollBoundsChange (callback func ()) {
+	element.onScrollBoundsChange = callback
+}
+
 // CountEntries returns the amount of entries in the list.
 func (element *List) CountEntries () (count int) {
 	return len(element.entries)

elements/basic/textbox.go

@@ -34,6 +34,7 @@ type TextBox struct {
 	
 	onKeyDown func (key input.Key, modifiers input.Modifiers) (handled bool)
 	onChange  func ()
+	onScrollBoundsChange func ()
 }
 
 // NewTextBox creates a new text box with the specified placeholder text, and
@@ -241,6 +242,12 @@ func (element *TextBox) OnChange (callback func ()) {
 	element.onChange = callback
 }
 
+// OnScrollBoundsChange sets a function to be called when the element's viewport
+// bounds, content bounds, or scroll axes change.
+func (element *TextBox) OnScrollBoundsChange (callback func ()) {
+	element.onScrollBoundsChange = callback
+}
+
 // ScrollContentBounds returns the full content size of the element.
 func (element *TextBox) ScrollContentBounds () (bounds image.Rectangle) {
 	bounds = element.valueDrawer.LayoutBounds()