Make a child visual that is a window to the parent
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. manpage:: 7 display-sub


Description
-----------

Creates a "child" visual within a "parent". This can be thought of as
a window and the `display-sub` target is intended for simple windowing
systems.

No textual arguments, since this target can only be used by
applications. :p:`argptr` must contain the parent visual.

The sub target behaves a bit special with respect to (i.e. abuses the
semantics of :) the :man:`ggiSetMode(3)` call. It uses the "visible"
size for the top left corner position of the window within the visual,
and the "virtual" size for window width and height.  Note, that
moving/resizing the window does *not* cause any drawing action.  You
have to perform those yourself. All it does for you is providing a
virtual visual within an existing one, which is convenient to allow
for window system canvases to be about any GGI program.


Features
--------

- DirectBuffer not supported.

- Accelerated to the point of the parent. Calls are mapped through
  with modified clipping and coordinates.
