Rule

koto::Rule draws a horizontal divider line across the vertical center of an area with an optional space-padded title (Header: koto/rule.hpp).

Quick example

Titled rule

Rule("Section")
    .style(BorderStyle::Double)
    .title_align(TitleAlign::Center)
    .fg(Color::Cyan)
    .title_fg(Color::White)
    .draw(frame, rule_area);

Output

════════════ Section ═════════════

Behavior

• Vertical centering: Rule::draw() draws on a single row at row = area.row + (area.height - 1) / 2 (src/rule.cpp:64). Rows above and below row in area are untouched.
• Line glyph selection: BorderStyle::Single and BorderStyle::Rounded use U'─', BorderStyle::Double uses U'═', BorderStyle::Thick uses U'━', and BorderStyle::None uses U' ' (src/rule.cpp:66-83).
• Title padding and alignment: When m_title is non-empty, Rule constructs padded = " " + m_title + " " and measures title_w = text_width(padded). If title_w > area.width, the title is skipped and the solid line remains intact. Otherwise:
  • TitleAlign::Left places padded at area.col + 2 (clamped to [area.col, area.right() - title_w]).
  • TitleAlign::Center places padded at area.col + (area.width - title_w) / 2.
  • TitleAlign::Right places padded at area.right() - 2 - title_w (clamped to [area.col, area.right() - title_w]).
• Title color fallback: If m_title_fg == COLOR_DEFAULT, the title uses m_fg; if m_title_bg == COLOR_DEFAULT, the title uses m_bg (src/rule.cpp:122-123).

Methods

Method	Description	Default
Rule(std::string_view title = "")	Constructs a Rule with an optional title string.	title = ""
title(std::string_view title)	Sets the embedded title text.	""
title_align(TitleAlign align)	Sets horizontal title alignment (Left, Center, Right).	TitleAlign::Center
style(BorderStyle style)	Sets the horizontal line glyph style (Single, Rounded, Double, Thick, None).	BorderStyle::Single
fg(Color fg)	Sets the line foreground color (and fallback title foreground).	COLOR_DEFAULT
bg(Color bg)	Sets the line background color (and fallback title background).	COLOR_DEFAULT
title_fg(Color fg)	Sets an explicit foreground color for the padded title.	COLOR_DEFAULT (falls back to fg)
title_bg(Color bg)	Sets an explicit background color for the padded title.	COLOR_DEFAULT (falls back to bg)
draw(Frame& frame, Area area)	Renders the horizontal rule into frame within area.	None

Gotchas

• Method name is .style(...), not .border_style(...): Unlike Box, Button, List, Tabs, TextArea, and TextInput, Rule names its BorderStyle setter .style(BorderStyle) (include/koto/rule.hpp:19).
• No .id(...) method: Rule is a purely decorative divider and does not expose .id(Id).

See also

• Box
• Text