Struct ScrollingComponent 

pub struct ScrollingComponent {
    pub viewport_height: f32,
    pub content_height: f32,
    pub scroll_offset: f32,
    pub track: Option<ComponentId>,
    pub track_base_pos: [f32; 3],
    pub drag_scope: Option<ComponentId>,
    /* private fields */
}

Generic scroll state for moving a content track inside a clipped viewport.

ScrollingComponent does not own clipping; it only tracks viewport/content sizes, current offset, which transform should be moved by the scroll runtime, and the drag scope currently bridged into scroll events.

Expected topology:

viewport_root                  ← usually clipped by StyleComponent::overflow
  └── ScrollingComponent       ← owned by ScrollingSystem
        └── scroll_track       ← moved in +Y as scroll_offset increases
              ├── child_0
              ├── child_1
              └── ...

If no explicit track is assigned, ScrollingSystem now creates an internal Router plus an owned __scroll_track transform under the ScrollingComponent, and routed children are sent there both at init time and on later direct attaches.

Fields

viewport_height: f32

Height of the clipped viewport in scroll-local/layout units.

content_height: f32

Height of the scrollable content in scroll-local/layout units.

scroll_offset: f32

Current scroll offset in scroll-local/layout units. 0.0 = top.

track: Option<ComponentId>

Transform moved by the scroll runtime.

If unset at init time, the runtime will create an owned internal track by default.

track_base_pos: [f32; 3]

Base local-space position of track before any scrolling is applied.

drag_scope: Option<ComponentId>

Ancestor scope currently forwarding drag motion into this scrolling component.

Implementations

impl ScrollingComponent

pub fn new(viewport_height: f32, content_height: f32) -> Self

pub fn set_track(&mut self, track: ComponentId, base_pos: [f32; 3])

pub fn set_drag_scope(&mut self, drag_scope: ComponentId)

pub fn set_content_height(&mut self, content_height: f32) -> bool

pub fn max_scroll(&self) -> f32

Maximum scroll distance in scroll-local/layout units.

pub fn apply_drag(&mut self, delta_y: f32) -> bool

Update scroll_offset by a scroll-local Y drag delta.

Sign convention: dragging up (positive delta_y) reveals content lower in the list.

pub fn track_translation(&self) -> [f32; 3]

Current translation that should be applied to the scroll track.

pub fn clamp_to_content(&mut self) -> bool

Clamp scroll after content size changes. Returns true if the position changed.

Trait Implementations

impl Clone for ScrollingComponent

fn clone(&self) -> ScrollingComponent

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Component for ScrollingComponent

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

Short debug/type name for this component kind (e.g. “transform”, “camera”).

fn set_id(&mut self, id: ComponentId)

fn as_any(&self) -> &dyn Any

fn as_any_mut(&mut self) -> &mut dyn Any

fn init(&mut self, emit: &mut dyn SignalEmitter, component: ComponentId)

Called when component is added to the World

fn to_mms_ast(&self, _world: &World) -> ComponentExpression

Encode this component as an MMS Component Expression AST node.

fn cleanup(&mut self, _emit: &mut dyn SignalEmitter, _component: ComponentId)

Called when component is removed from the World.

fn encode(&self) -> HashMap<String, Value>

Encode component data to a HashMap for serialization.

fn decode(&mut self, _data: &HashMap<String, Value>) -> Result<(), String>

Decode component data from a HashMap after deserialization.

impl Debug for ScrollingComponent

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

Formats the value using the given formatter.