Centering.tex

\section{Centering}
\label{sec:centering}

The \fw{Centering} module provides widgets for centering other widgets
horizontally and vertically:

\begin{itemize}
\item \fw{hCentered} -- takes a \fw{Widget a} and centers it
  horizontally.  Returns a value of type \fw{Widget (HCentered a)}.
\item \fw{vCentered} -- takes a \fw{Widget a} and centers it
  vertically.  Returns a value of type \fw{Widget (VCentered a)}.
\item \fw{centered} -- takes a \fw{Widget a} and centers it both
  horizontally and vertically using \fw{hCentered} and \fw{vCentered}.
  Returns a value of type \fw{Widget (VCentered (HCentered a))}.
\end{itemize}

Horizontal and vertical centering are only useful if the widget being
centered doesn't grow to fill the available space on its own, since it
would be as large as the available space and thus would be centered
implicitly.  To constrain a growing widget to make it centerable, see
Sections \ref{sec:limits} and \ref{sec:fixed}.

\subsubsection{Growth Policy}

\fw{HCentered} widgets always grow horizontally and defer to their
children for vertical growth policy.  Likewise, \fw{VCentered} widgets
always grow vertically and defer to their children for horizontal
growth policy.  The \fw{centered} function returns a widget which
always grows in both directions.