Struct RowViewport 

pub struct RowViewport { /* private fields */ }

A viewport of uniform-height rows: which item is on top, and how pointer rows map back to items.

List-shaped components scroll by item, not by screen row, and hit-test a click by pure arithmetic: divide the pointer’s row by the per-item height, add the offset that was painted. That only works when two things hold — every item is the same height, and the offset used for hit-testing is the one actually painted. This type holds both: the per-item height, and the painted offset — the top-item index the last render actually drew, recorded with record_painted_offset so event-time arithmetic works against what is on screen rather than against app state that may be one frame newer.

The viewport is render-derived runtime state, not a second copy of app-owned scroll: a component that binds scroll still reads the requested offset from app state each frame and resolves it through cursor_visible_offset.

Implementations

impl RowViewport

pub const fn new(row_height: u16) -> Self

A viewport whose items each occupy row_height terminal rows. A height of 0 is treated as 1, so the divisions below stay safe.

pub const fn rows_per_item(&self) -> u16

Terminal rows each item occupies. Never 0.

pub const fn painted_offset(&self) -> usize

The top-item index the last render drew, as recorded by record_painted_offset. 0 before the first render.

pub const fn record_painted_offset(&mut self, offset: usize)

Record the offset this frame is about to paint, so later events hit-test against it.

pub const fn visible_items(&self, area: Rect) -> usize

How many whole items fit in area. This is the unit paging and scrolling work in — screen rows are only a paint concern.

pub fn row_at( &self, area: Rect, len: usize, column: u16, row: u16, ) -> Option<usize>

The item index under the pointer at (column, row), using the painted offset, or None outside area or past the last of len items.

Several screen rows can belong to one item, so the pointer row is divided by the per-item height before the lookup — otherwise a click on an item’s second line would hit the wrong item.

pub fn cursor_visible_offset( &self, area: Rect, len: usize, requested: usize, cursor: Option<usize>, ) -> usize

The offset that keeps cursor visible in area, starting from a requested offset — linear_nav::cursor_visible_offset measured in this viewport’s items.

Trait Implementations

impl Clone for RowViewport

fn clone(&self) -> RowViewport

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for RowViewport

impl Debug for RowViewport

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

Formats the value using the given formatter.

impl Eq for RowViewport

impl PartialEq for RowViewport

fn eq(&self, other: &RowViewport) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for RowViewport