NAME
    `Tickit::Widget::ScrollBox' - allow a single child widget to be scrolled

SYNOPSIS
     use Tickit;
     use Tickit::Widget::ScrollBox;
     use Tickit::Widget::Static;

     my $scrollbox = Tickit::Widget::ScrollBox->new(
        child => Tickit::Widget::Static->new(
           text => join( "\n", map { "The content for line $_" } 1 .. 100 ),
        ),
     );

     Tickit->new( root => $scrollbox )->run;

DESCRIPTION
    This container widget draws a scrollbar beside a single child widget and
    allows a portion of it to be displayed by scrolling.

STYLE
    Th following style pen prefixes are used:

    scrollbar => PEN
        The pen used to render the background of the scroll bar

    scrollmark => PEN
        The pen used to render the active scroll position in the scroll bar

    arrow => PEN
        The pen used to render the scrolling arrow buttons

    The following style keys are used:

    arrow_up => STRING
    arrow_down => STRING
    arrow_left => STRING
    arrow_right => STRING
        Each should be a single character to use for the scroll arrow
        buttons.

    The following style actions are used:

    up_1 (<Up>)
    down_1 (<Down>)
    left_1 (<Left>)
    right_1 (<Right>)
        Scroll by 1 line

    up_half (<PageUp>)
    down_half (<PageDown>)
    left_half (<C-Left>)
    right_half (<C-Right>)
        Scroll by half of the viewport

    to_top (<C-Home>)
    to_bottom (<C-End>)
    to_leftmost (<Home>)
    to_rightmost (<End>)
        Scroll to the edge of the area

CONSTRUCTOR
  $scrollbox = Tickit::Widget::ScrollBox->new( %args )
    Constructs a new `Tickit::Widget::ScrollBox' object.

    Takes the following named arguments in addition to those taken by the
    base Tickit::SingleChildWidget constructor:

    vertical => BOOL or "on_demand"
    horizontal => BOOL or "on_demand"
            Whether to apply a scrollbar in the vertical or horizontal
            directions. If not given, these default to vertical only.

            If given as the string `on_demand' then the scrollbar will be
            optionally be displayed only if needed; if the space given to
            the widget is smaller than the child content necessary to
            display.

ACCESSORS
  $vextent = $scrollbox->vextent
    Returns the Tickit::Widget::ScrollBox::Extent object representing the
    box's vertical scrolling extent.

  $hextent = $scrollbox->hextent
    Returns the Tickit::Widget::ScrollBox::Extent object representing the
    box's horizontal scrolling extent.

METHODS
  $scrollbox->scroll( $downward, $rightward )
    Requests the content be scrolled downward a number of lines and
    rightward a number of columns (either of which which may be negative).

  $scrollbox->scroll_to( $top, $left )
    Requests the content be scrolled such that the given line and column
    number of the child's content is the topmost visible in the container.

SMART SCROLLING
    If the child widget declares it supports smart scrolling, then the
    ScrollBox will not implement content scrolling on its behalf. Extra
    methods are used to co-ordinate the scroll position between the
    scrolling-aware child widget and the containing ScrollBox. This is
    handled by the following methods on the child widget.

    If smart scrolling is enabled for the child, then its window will be set
    to the viewport directly, and the child widget must offset its content
    within the window as appropriate. The child must indicate the range of
    its scrolling ability by using the `set_total' method on the extent
    object it is given.

  $smart = $child->CAN_SCROLL
    If this method exists and returns a true value, the ScrollBox will use
    smart scrolling. This method must return a true value for this to work,
    allowing the method to itself be a proxy, for example, to proxy
    scrolling information through a single child widget container.

  $child->set_scrolling_extents( $vextent, $hextent )
    Gives the child widget the vertical and horizontal scrolling extents.
    The child widget should save thes values, and inspect the `start' value
    of them any time it needs these to implement content offset position
    when rendering.

  $child->scrolled( $downward, $rightward, $h_or_v )
    Informs the child widget that one of the scroll positions has changed.
    It passes the delta (which may be negative) of each position, and a
    string which will be either `"h"' or `"v"' to indicate whether it was an
    adjustment of the horizontal or vertical scrollbar. The extent objects
    will already have been updated by this point, so the child may also
    inspect the `start' value of them to obtain the new absolute offsets.

TODO
    *   Choice of left/right and top/bottom bar positions.

    *   Click-and-hold on arrow buttons for auto-repeat

    *   Allow smarter cooperation with a scrolling-aware child widget;
        likely by setting extent objects on the child if it declares to be
        supported, and use that instead of an offset child window.

AUTHOR
    Paul Evans <leonerd@leonerd.org.uk>