Vbox

koto::Vbox is a composite Widget container that owns child widgets via std::unique_ptr<Widget> and draws them top-to-bottom using Layout::vertical (Header: koto/vbox.hpp).

Quick example

Vertical box container

Vbox col;
col.add<Box>(Constraint::fixed(3)).title("Top").border_style(BorderStyle::Rounded);
col.add<Box>(Constraint::fill()).title("Bottom").border_style(BorderStyle::Single);
col.draw(frame, vbox_area);

Output

╭─────────── Top ────────────╮
│                            │
╰────────────────────────────╯
┌────────── Bottom ──────────┐
│                            │
└────────────────────────────┘

Behavior

• Child ownership and fluent chaining: Vbox::add<T>(Constraint c, Args&&... args) allocates a std::unique_ptr<T>(std::forward<Args>(args)...), appends {std::move(widget), c} to m_children, and returns a T& reference so you can chain configuration calls on the newly added child (include/koto/vbox.hpp:15-25).
• Nesting Hbox and Vbox: Because both Vbox and Hbox derive from koto::Widget, you can nest an Hbox inside a Vbox via auto& row = vbox.add<Hbox>(Constraint::fill()); and populate row.add<...>(...).
• Stack constraint buffer for <= 16 children: When m_children.size() <= LayoutResult::InlineCapacity (16), Vbox::draw() copies the child constraints into a stack std::array<Constraint, 16>, calls Layout::vertical(area, std::span<const Constraint>(...)), and draws each child into rect[i] (src/vbox.cpp:16-28).

Methods

Method	Description	Default
Vbox()	Default-constructs an empty vertical container (move-only due to std::unique_ptr<Widget>).	m_children empty
add<T>(Constraint c, Args&&... args)	Constructs child widget T(args...) with vertical constraint c, stores it, and returns T&.	None
draw(Frame& frame, Area area)	Partitions area vertically and draws each child into its corresponding sub-area.	None

Gotchas

• Per-child heap allocation in add<T>: Calling vbox.add<T>(...) invokes std::make_unique<T>(...). To avoid heap allocations inside on_render, either construct a static Vbox when children do not depend on per-frame state or use Layout::vertical(area, {...}) with stack-allocated widgets.

See also

• Hbox
• Layout
• Layout Recipes Guide