Enum VirtualMode 

pub enum VirtualMode {
    Fixed {
        row_height: f32,
    },
    Dynamic {
        estimated_row_height: f32,
        append_only: bool,
    },
}

Virtualized list state attached to a Kind::VirtualList node. Holds the row count, the row-height policy, and the closure that realizes a row by global index. Set via crate::virtual_list or crate::virtual_list_dyn; the layout pass calls build_row(i) only for indices whose rect intersects the viewport.

Row-height policies

• VirtualMode::Fixed — every row is the same logical-pixel height. Scroll → visible-range is O(1).
• VirtualMode::Dynamic — rows vary in height. The library uses estimated_row_height as a placeholder for unmeasured rows, measures visible rows at the current layout width, and preserves a row anchor on screen while estimates become measurements.

Other current scope

• Vertical only — feed/chat-log-shaped lists are the target. A horizontal variant can come later.
• No row pooling — visible rows are rebuilt from scratch each layout pass. Fine for thousands of items; if it bottlenecks we add a pool keyed by stable row keys.

Variants

Fixed

Every row is exactly row_height logical pixels tall.

Fields

row_height: f32

Uniform row height in logical pixels. Must be > 0.

Dynamic

Rows have variable heights. estimated_row_height seeds the content-height total and the visible-range walk for rows that haven’t been measured yet.

Fields

estimated_row_height: f32

Placeholder height (logical pixels) for not-yet-measured rows. Must be > 0.

append_only: bool

Opt-in contract: across frames the row sequence changes only by appending rows at the tail and/or dropping a contiguous prefix at the head (an append-at-bottom feed or a capped ring buffer). When set, layout maintains an incremental per-row height index so the per-frame cost is O(visible) instead of several O(n) walks — the difference that lets a 100k-row chat log stay inside frame budget while scrolling (issue #107). Reordering, mid-list insertion, or re-keying a surviving row violates the contract: debug builds assert, release self-heals with a one-frame O(n) rebuild. Set via VirtualItems::append_only / crate::tree::El::append_only.

Trait Implementations

impl Clone for VirtualMode

fn clone(&self) -> VirtualMode

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for VirtualMode

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

Formats the value using the given formatter.