Layout

Divide the screen with constraints, and split it into resizable panes.

Fluent builder for creating named layout regions. Sizes are computed with exact integer arithmetic: regions never overlap, never leave the area, and rounding never drops a cell.

var layout = Layout.Vertical(screen)
    .Add("header", Constraint.Length(3))    // Exactly 3 rows (shrunk only if fixed sizes don't fit)
    .Add("content", Constraint.Fill())      // Fill remaining space
    .Add("footer", Constraint.Length(1))
    .Spacing(1)                             // Optional: empty cells between regions
    .Build();                               // Optional: the indexer builds on first use

buf.SetString(layout["header"].X, layout["header"].Y, "Title", Style.Default.Bold());
Widget.List().Items(items).Draw(buf, layout["content"]);

var columns = Layout.Split(area, Direction.Horizontal, Constraint.Percentage(30), Constraint.Fill());

Constraint	Size
`Length(n)`	n cells
`Percentage(p)`, `Ratio(a, b)`	that share of the space, rounded down
`Min(n)`	at least n, then grows like `Fill(1)`
`Max(n)`	grows like `Fill(1)`, up to n
`Fill(weight)`	shares the leftover in proportion to `weight`

When the fixed sizes don't fit, Length, Percentage and Ratio shrink proportionally first, then Min. Space that nothing can grow into is placed by .Flex(Flex.Start | End | Center | SpaceBetween). .Margin(new Margin(1)) insets the area first.

Split panes

Widget.Split(state) divides an area into two panes with a one-cell divider and returns them for you to draw into. The user drags the divider (with WithMouse()) or moves it with Alt+Shift and the arrows. A SplitState is sized by Ratio (the panes scale with the terminal) or, with SplitState.Fixed(direction, cells, pane), keeps one pane at a size in cells, such as a sidebar. MinFirst and MinSecond (3 by default) limit how small the user can make each pane, and Changed fires when they move it. Splits nest:

private readonly SplitState _sidebar = SplitState.Fixed(Direction.Horizontal, 24);

public override bool HandleMouse(MouseEvent mouse) => _sidebar.HandleMouse(mouse);
public override bool HandleKey(ConsoleKeyInfo key) => _sidebar.HandleKey(key);

public override void Render(CellBuffer buf, Rect area, RenderContext ctx)
{
    var (left, right) = Widget.Split(_sidebar).Draw(buf, area);
    ctx.Render(_files, buf, left);
    ctx.Render(_preview, buf, right);
}

Focused children see keys first, and the list, scroll and tree states take arrows with any modifier, so a pane built on them passes Alt keys on to keep Alt+Shift+arrows for the split. The text states leave Alt with the arrows, Home and End unhandled too.

Table of Contents

Layout

Split panes