Struct ScrollArea 

pub struct ScrollArea { /* private fields */ }

A clipping viewport that makes any child widget scrollable.

The scroll offset per axis is stored in a reactive Signal<f32>, shared with the built-in ScrollBar children. See ScrollBarMode for display options and ScrollBarPolicy for per-axis visibility control.

Implementations

impl ScrollArea

pub fn new() -> Self

Create a new ScrollArea with overlay scroll bars, smooth scrolling, and no content yet.

pub fn child(self, child: impl Widget + 'static) -> Self

Set the scrollable content widget.

pub fn from_id(child: WidgetId) -> Self

Construct from an already-registered child WidgetId.

pub fn scroll_bar_style(self, style: ScrollBarMode) -> Self

Set the scroll bar display mode (Overlay, Permanent, or Thin).

pub fn scroll_bar_thumb_color(self, color: impl Into<ColorProp>) -> Self

Tint the built-in scroll bars’ thumb with an explicit colour instead of the theme’s scrollbar_thumb* tokens. Accepts anything impl Into<ColorProp> — a Color, a theme role, or a Signal — resolved against the live theme at paint, so roles/signals stay reactive. Forwarded to both scroll bars via ScrollBar::thumb_color. Use when the area sits on a surface the surface-relative tokens don’t suit — e.g. a tooltip’s inverse chip (TextRole::TooltipText).

pub fn vertical_scroll_bar_policy(self, policy: ScrollBarPolicy) -> Self

Set the vertical scroll bar visibility policy.

pub fn horizontal_scroll_bar_policy(self, policy: ScrollBarPolicy) -> Self

Set the horizontal scroll bar visibility policy.

pub fn line_height(self, lh: f32) -> Self

Set the pixels-per-line used when translating line-based wheel events.

pub fn scroll_bar_thickness(self, thickness: f32) -> Self

Set the scroll bar thickness in logical pixels (applies to both axes).

pub fn widget_resizable(self, resizable: bool) -> Self

When true, content smaller than the viewport is stretched to fill it. Similar to Qt’s QScrollArea::setWidgetResizable(true).

pub fn smooth_scrolling(self, enabled: bool) -> Self

Enable or disable smooth animated scrolling for wheel events. Enabled by default. Applies to both line-based (ScrollDelta::Lines) and pixel-based (ScrollDelta::Pixels) wheel events — on Wayland and other platforms with high-resolution scroll axes, mouse wheel notches are delivered as pixel deltas, so animating both paths is required for a fast flick to feel smooth instead of jumping.

pub fn smooth_scroll_duration(self, duration: Duration) -> Self

Set the duration of the smooth scroll animation (default: 150ms).

pub fn scroll_past_end(self, fraction: impl Into<Prop<f32>>) -> Self

Allow scrolling past the end of the content by fraction of the viewport height (default 0.0 — the last pixel of content stops flush with the bottom of the viewport).

This extends the scroll range only. It adds no widget, no padding and no layout, so it cannot interfere with the content’s own padding — a distinction worth keeping, since padding-based implementations of this idea in other toolkits are a recurring source of “single-line content is scrollable” bugs.

The motivating case is typewriter scrolling: to pin the caret’s line at the middle of the viewport, the view must be able to scroll half a viewport past the last line, or the pin quietly stops working over the final page — exactly where a writer spends their time. Pair with EventContext::ensure_visible_aligned, passing 1.0 - fraction here for a pin at fraction.

Accepts a literal or a Signal<f32>, so it can follow a setting live. Negative values are treated as 0.0.

pub fn preferred_size(self, width: f32, height: f32) -> Self

Set a preferred size returned when the parent proposes unconstrained dimensions. If not set, falls back to cached content size or 300×200.

This overrides both axes. If you only want to cap the height and let the width follow the content — the usual case for a menu or popover, which must be as wide as its widest row — use preferred_height instead. Passing a width of 0.0 here does not mean “no preference”: it means zero, and the scroll area will collapse.

pub fn preferred_height(self, height: f32) -> Self

Cap the height when the parent proposes an unconstrained one, while letting the width continue to follow the content.

This is what a scrolling menu/popover wants: it must not grow taller than its viewport, but it must still be as wide as its widest item. Using preferred_size with a 0.0 width for this collapses the panel to its minimum width and clips every row — the parent proposes an unconstrained width (it is hugging its content), so the 0.0 is taken literally.

pub fn overscroll_behavior(self, behavior: OverscrollBehavior) -> Self

Set the scroll-chaining behavior at the boundary. Default OverscrollBehavior::Chain (a boundary scroll bubbles to an ancestor scrollable); OverscrollBehavior::Contain absorbs it instead.

pub fn restore_scroll_y(self, offset: f32) -> Self

Land offset on the first layout pass at which this area has a real scrollable range, then forget it.

max_scroll_y is 0.0 until the content has been measured, so an offset a host writes before that first measurement is clamped away to zero and the page paints at the top for a frame before jumping to where it should have started. This stores the offset instead and applies it itself, inside layout, as soon as max_scroll_y becomes nonzero, before the ordinary clamp would otherwise discard it, so the very first frame the content is measured on is already laid out at the restored position, with no visible jump.

It is a one-shot: once applied, it is dropped, so a later reflow (a wider window, an edit that lengthens the document) never yanks the reader back to where they came in. The offset is still clamped to the real range when it lands: past the end it lands at the end, negative it lands at zero.

offset <= 0.0 is a no-op: there is nothing to restore, and it clears any previously armed offset rather than leaving it pending.

An area that never calls this behaves exactly as it always has.

pub fn scroll_y_signal(&self) -> &Signal<f32>

Get the vertical scroll position signal (for external observation).

pub fn scroll_x_signal(&self) -> &Signal<f32>

Get the horizontal scroll position signal (for external observation).

pub fn max_scroll_y_signal(&self) -> &Signal<f32>

Maximum vertical scroll offset for the current content (content_height − viewport_height, or 0 when content fits), plus any range bought with scroll_past_end. External callers bind to this for “is there more to scroll?” chrome (e.g. trailing scroll-arrow visibility).

pub fn viewport_ratio_y_signal(&self) -> &Signal<f32>

Fraction of the scrollable height currently visible (1.0 when everything fits) — what sizes the vertical scroll bar’s thumb. Accounts for scroll_past_end, so the thumb stays proportional to the range the user can actually travel.

pub fn max_scroll_x_signal(&self) -> &Signal<f32>

Maximum horizontal scroll offset for the current content. External callers bind to this for “is there more to scroll?” chrome (e.g. trailing scroll-arrow visibility on a tab bar).

Trait Implementations

impl Debug for ScrollArea

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for ScrollArea

fn default() -> Self

Returns the “default value” for a type.

impl Widget for ScrollArea

fn as_any(&self) -> Option<&dyn Any>

Opt into concrete-type introspection so a host’s tests can read the scroll metrics of an area built deep inside a composite (a page whose ScrollArea no caller holds a reference to) rather than only of one they constructed themselves.

fn build(&mut self, ctx: &mut BuildContext<'_>) -> Vec<WidgetId>

Compose child widgets. Called once after the widget is placed in the arena, and again on environment change (theme switch, locale switch). Takes &mut self — store child IDs, signal handles, any state needed later. Returns the list of root child IDs (empty for leaf widgets).

fn layout_response( &self, proposal: SizeProposal, ctx: &LayoutContext<'_>, ) -> LayoutResponse

Respond to the parent’s size proposal with this widget’s wanted size, grow/shrink weights, and compression floor (see [LayoutResponse]).

fn place_children( &self, bounds: Rect, _proposal: SizeProposal, children: &mut [WidgetPlacement], ctx: &LayoutContext<'_>, )

Position children within the allocated bounds.

fn paint(&self, _bounds: Rect, _canvas: &mut Canvas, _ctx: &PaintContext<'_>)

Draw the widget’s visual representation.

fn children(&self) -> Vec<WidgetId>

Return the child widget IDs that this widget manages.

fn accessibility(&self, builder: &mut AccessNodeBuilder)

Declare this widget’s accessibility identity.

fn type_name(&self) -> &'static str

Concrete type name of this widget (e.g. "teksilo_widgets::button::Button"). The default implementation resolves at the impl site via std::any::type_name::<Self>(), so calls through &dyn Widget correctly dispatch to the monomorphized fn for the concrete type — getting the concrete name through the vtable without per-impl boilerplate.

fn cacheable_layout(&self) -> bool

Whether this widget’s layout_response may be memoized by the per-pass layout cache. Defaults to true.

fn wants_after_paint(&self) -> bool

Whether this widget wants its after_paint hook to fire each frame. Returning false (the default) saves a virtual call per widget per frame for the vast majority of widgets that don’t aggregate descendant geometry.

fn after_paint(&self, _view: &WidgetTreeView<'_>, _ctx: &PaintContext<'_>)

Called once per frame after this widget’s subtree has finished painting. Receives a read-only view of the layout-resolved arena so a parent can read its descendants’ final bounds — e.g. TitleBar aggregates its drag region and control-button rects into a single HitRegions payload for the Windows backend’s WM_NCHITTEST.

fn wants_post_paint(&self) -> bool

Whether this widget wants its post_paint hook to fire each frame. Returning false (the default) saves a virtual call per widget per frame for the vast majority of widgets that don’t draw a foreground over their children.

fn post_paint( &self, _bounds: Rect, _canvas: &mut Canvas, _ctx: &PaintContext<'_>, )

Draw a foreground layer over this widget’s children.

fn wants_descendant_redirects(&self) -> bool

Whether this widget wants the AT walker to consult its a11y_redirect_descendant hook for every descendant during AT tree emission, not just its direct arena children.

fn a11y_redirect_descendant( &self, _self_id: WidgetId, _descendant: WidgetId, ) -> Option<NodeId>

Optional redirection hook for AT-tree placement of a child.

fn accessible_title_hint(&self) -> Option<String>

Suggest an accessible title to an enclosing container that wraps this widget as content — typically a modal / dialog shell that wants to propagate the inner content’s visible title as the shell’s own accessible name.

fn initial_focus_hint(&self) -> Option<WidgetId>

Optional hint that directs initial focus to a specific descendant when this widget is the root of a deferred-built modal surface.

fn accessibility_children(&self) -> Option<Vec<WidgetId>>

Optional override for the child ORDER presented to assistive technology, when it must differ from the paint / z-order child order returned by children.

fn as_any_mut(&mut self) -> Option<&mut (dyn Any + 'static)>

Mutable counterpart of as_any. Default returns None; widgets that want to expose mutable state to tests (e.g. so a test can mutate a Scene inside a SceneView post-layout) override with Some(self). Should follow the same opt-in pattern as as_any: only widgets that opt into & introspection should opt into &mut.

fn clips_children(&self) -> bool

Whether this widget clips its children to its bounds.

fn focus_reveal_rect(&self, _bounds: Rect) -> Option<Rect>

The rectangle (in absolute tree coordinates) that best represents this widget when the framework reveals it into an ancestor scroll area on focus gain. Returning None (the default) reveals the widget’s whole bounds — correct for most controls.

fn hit_shape(&self, _local_point: Point, _bounds: Rect) -> bool

Whether the point lies inside this widget’s actual shape, not just its rectangular bounds. Consulted by hit-testing right after the bounds check: returning false for a point that is inside the bounding box makes the widget transparent to the click there, so it falls through to whatever sibling is painted underneath (the same machinery as a fully pass-through node, but shape-aware).

fn preserves_children_on_rebuild(&self) -> bool

How rebuild_single_widget treats this widget’s existing children when re-running its build().

fn tooltip_has_content(&self) -> bool

Whether this widget, used as tooltip content, currently has anything worth showing.

fn declare_shortcuts(&self) -> Vec<Shortcut>

Declare the rebindable keyboard shortcuts this widget exposes, without installing handlers. The framework calls this at arena insertion time (before build()) and at certain lazy boundaries (e.g. Switcher walks declarations on its not-yet-mounted Pending slots), so settings UIs and the ShortcutRegistry see the keystrokes the moment the owning container mounts — even if build() hasn’t run.

fn take_handler_set(&mut self) -> Option<HandlerSet>

Extract attached handler set from a WidgetWithHandlers wrapper. Called during arena insertion to transfer handlers to the WidgetNode. Default: returns None (no attached handlers).