SceneScrollView

SceneScrollView — a thin composite that gives a SceneView draggable scroll bars, mirroring the widget-tier ScrollArea's options: the same ScrollBarMode (Overlay / Permanent / Thin, with its Tier-3 ScrollBarStyle), per-axis ScrollBarPolicy (AsNeeded / AlwaysOn / AlwaysOff), and thickness. Smooth wheel / keyboard panning and the overscroll policy stay configured on the wrapped SceneView itself (it already animates pan and honours reduced-motion); the scroll bars simply track that motion.

Why a wrapper

A SceneView wraps its entire child subtree in the pan/zoom view transform (via set_content_transform), so scroll bars added as its own children would pan and zoom along with the content. Instead — exactly like ScrollArea wraps arbitrary content and SceneMinimap is a sibling overlay — this widget hosts the SceneView as content plus two reusable ScrollBar children outside the transform, and bridges the bars' scroll signals to the view's pan_x/pan_y.

How the bridge works

The scene's scrollable extent is its effective pan bounds (the Scene-declared pan_bounds intersected with any view-level pan_bounds_override), falling back to the union of item bounds. With the standard view transform screen = zoom*scene + pan + bounds_origin and the SceneView placed flush at this widget's origin (so bounds_origin cancels the viewport's screen offset), the per-axis mapping in screen-pixel units is:

scroll_pos_x   = -pan_x - extent.x * zoom
max_scroll_x   = (extent.width * zoom - viewport_width).max(0)
viewport_ratio = viewport_width / (extent.width * zoom)

and the inverse, when a bar writes a new scroll_pos_x:

pan_x = -extent.x * zoom - scroll_pos_x

The display direction (camera → bar metrics) is recomputed each place_children — the same place ScrollArea computes its metrics — so it never lags a layout pass. The interaction direction (bar drag → pan) is a pair of guarded effects, one per axis, that snap the pan immediately so the thumb tracks the cursor 1:1 (the desktop scroll-bar convention). Both use an epsilon equality guard (the color_picker bidirectional-bridge idiom) so a write arriving from the opposite direction is a no-op and the loop closes — in particular the bars track the SceneView's own smooth wheel / keyboard pan animation without fighting it.

Rotation is supported but approximate: the mapping is exact only when rotation == 0; while rotated the thumbs track the camera using the axis-aligned formula above.

Builder methods at a glance

scroll_bar_mode, vertical_policy, horizontal_policy, scroll_bar_thickness, scroll_pos_x_signal, scroll_pos_y_signal, max_scroll_x_signal, max_scroll_y_signal, viewport_ratio_x_signal, viewport_ratio_y_signal

API reference

📖 Full rustdoc API for this module

`pub struct SceneScrollView`

A SceneView with draggable scroll bars.

Construct directly from a configured view, or via the SceneView::with_scroll_bars convenience method:

#![allow(unused)]
fn main() {
use teksilo_scene::{Scene, SceneView, SceneScrollView, ScrollBarMode};
let scrollable = SceneView::new(Scene::new())
    .with_scroll_bars()
    .scroll_bar_mode(ScrollBarMode::Overlay);
let _ = scrollable;
}

#![allow(unused)]
fn main() {
pub struct SceneScrollView { /* fields */ }
}

Methods

`pub fn new(view: SceneView) -> Self`

Wrap a configured SceneView in a scroll-bar host. Captures the view's pan/zoom/model signals before moving it into the arena.

`pub fn scroll_bar_mode(mut self, mode: ScrollBarMode) -> Self`

Set the scroll-bar display mode (Overlay / Permanent / Thin).

`pub fn vertical_policy(mut self, policy: ScrollBarPolicy) -> Self`

Set the vertical scroll-bar visibility policy.

`pub fn horizontal_policy(mut self, policy: ScrollBarPolicy) -> Self`

Set the horizontal scroll-bar visibility policy.

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

Set the scroll-bar thickness (and the gutter width in Permanent mode).

`pub fn scroll_pos_x_signal(&self) -> &Signal<f32>`

Horizontal scroll position signal (screen-pixel units), for external observation. 0 = content's leading edge flush with the viewport.

`pub fn scroll_pos_y_signal(&self) -> &Signal<f32>`

Vertical scroll position signal (screen-pixel units).

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

Maximum horizontal scroll offset (extent.width*zoom - viewport_width, or 0 when the content fits). Bind for "is there more to scroll?" chrome.

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

Maximum vertical scroll offset.

`pub fn viewport_ratio_x_signal(&self) -> &Signal<f32>`

Horizontal viewport/content ratio (0.0..1.0) — the relative thumb size.

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

Vertical viewport/content ratio (0.0..1.0).

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