Struct Viewport 

pub struct Viewport {
    pub top_row: usize,
    pub top_col: usize,
    pub width: u16,
    pub height: u16,
    pub wrap: Wrap,
    pub text_width: u16,
    pub tab_width: u16,
}

Where the buffer is scrolled to and how big the visible area is.

Viewport is an input to crate::Buffer::ensure_cursor_visible, not a derived value. The host writes top_row, top_col, width, and height per render frame; the buffer clamps the cursor inside the declared area.

top_row and top_col are the first visible row / column; top_col is a char index, matching Position.

wrap and text_width together drive soft-wrap-aware scrolling and motion. text_width is the cell width of the text area (i.e. width minus any gutter the host renders) so the buffer can compute screen-line splits without duplicating gutter logic.

scroll_off is not a field on Viewport itself; the host computes it and adjusts top_row before handing the viewport to crate::Buffer::ensure_cursor_visible.

Wrap::None / crate::Wrap::Char / crate::Wrap::Word change which screen-row arithmetic the buffer uses. Switching mid-session is supported but the host must call crate::Buffer::ensure_cursor_visible afterwards.

Fields

top_row: usize

top_col: usize

width: u16

height: u16

wrap: Wrap

Soft-wrap mode the renderer + scroll math is using. Default is Wrap::None (no wrap, horizontal scroll via top_col).

text_width: u16

Cell width of the text area (after the host’s gutter is subtracted from the editor area). Used by wrap-aware scroll and motion code; ignored when wrap == Wrap::None. Set to 0 before the first frame; wrap math falls back to no-op then.

tab_width: u16

Cells per \t expansion stop. The renderer uses this to align tab characters; cursor_screen_pos uses it to map char column to visual column. 0 is treated as the renderer’s fallback (4) so hosts that don’t publish a value still render legibly.

Implementations

impl Viewport

pub const fn new() -> Self

pub fn effective_tab_width(self) -> usize

Effective tab width — falls back to 4 when tab_width == 0 so uninitialized viewports still expand tabs sensibly.

pub fn bottom_row(self) -> usize

Last document row that’s currently on screen (inclusive). Returns top_row when height == 0 so callers don’t have to special-case the pre-first-draw state.

pub fn contains(self, pos: Position) -> bool

True when pos lies inside the current viewport rect.

pub fn ensure_visible(&mut self, pos: Position)

Adjust top_row / top_col so pos is visible, scrolling by the minimum amount needed. Used after motions and after content edits that move the cursor.

Trait Implementations

impl Clone for Viewport

fn clone(&self) -> Viewport

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Viewport

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

Formats the value using the given formatter.

impl Default for Viewport

fn default() -> Viewport

Returns the “default value” for a type.

impl Copy for Viewport