/// Viewport represents the visible window into the buffer.
#[derive(Debug, Clone)]pubstructViewport{/// First visible line index (0-based).
puboffset:usize,
/// Number of visible lines.
pubheight:usize,
/// Number of visible columns.
pubwidth:usize,
}implDefault forViewport{fndefault()->Self{Self{
offset:0,
height:24,
width:80,}}}