Function set_scroll_offset

primitives/src/virtual/virtualizer.rs:88–126

Handle a scroll event. Writes reactive fields (`scroll_offset`, `is_scrolling`) which trigger component re-renders. Returns an optional correction to apply when scrolling stops.

(
    state: &Store<VirtualizerState>,
    measurements: &[VirtualItem],
    offset: u32,
    is_scrolling: bool,
)

///
/// Returns an optional correction to apply when scrolling stops.
pub fn set_scroll_offset(
    state: &Store<VirtualizerState>,
    measurements: &[VirtualItem],
    offset: u32,
    is_scrolling: bool,
) -> Option<i32> {
    let was_scrolling = *state.is_scrolling().peek();
    let mut correction = None;

    // Reset adjustments when user starts a new scroll
    if is_scrolling && !was_scrolling {
        state.scroll_adjustments().set(0);
        state.deferred_adjustments().set(0);
        // Freeze total size when scrolling starts to prevent scrollbar drift
        let total = calculate_total_size(measurements);
        state.stable_total_size().set(Some(total));
        state
            .stable_measurement_count()
            .set(Some(measurements.len()));
    }

    // When scrolling stops, apply accumulated deferred adjustments
    if !is_scrolling && was_scrolling {
        state.stable_total_size().set(None);
        state.stable_measurement_count().set(None);

        let deferred = *state.deferred_adjustments().peek();
        if deferred != 0 {
            correction = Some(deferred);
            state.deferred_adjustments().set(0);
        }
    }

    // Reactive writes – these trigger re-renders.
    state.scroll_offset().set(offset);
    state.is_scrolling().set(is_scrolling);

    correction
}

/// Set the viewport size. Reactive write.
pub fn set_viewport_size(state: &Store<VirtualizerState>, size: u32) {