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,
}

Visible region of a buffer — the runtime viewport state the host owns and mutates per render frame.

0.0.34 (Patch C-δ.1): semantic ownership moved from hjkl_buffer::Buffer to Host. The struct still lives in hjkl-buffer (alongside hjkl_buffer::Wrap and the rope-walking wrap_segments math it depends on) so the dependency graph stays engine → buffer; the engine re-exports it as crate::types::Viewport (this alias) for hosts that program to the SPEC surface.

The architectural decision is “viewport lives on Host, not Buffer”: vim logic must work in GUI hosts (variable-width fonts, pixel canvases, soft-wrap by pixel) as well as TUI hosts, so the runtime viewport state is expressed in cells/rows/cols and is owned by the host. top_row and top_col are the first visible row / column (top_col is a char index).

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

Mirrors what tui-textarea exposed today: the host publishes (width, height) from the render path each frame, and the buffer uses the cached values to clamp the cursor / scroll offsets when motions ask for it. 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.

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.

Implementations

impl Viewport

pub const fn new() -> Viewport

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<(), Error>

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