## Copyright (C) 2005-2012 John W. Eaton
##
## This file is part of Octave.
##
## Octave is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 3 of the License, or (at
## your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING.  If not, see
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn  {Command} {} hold
## @deftypefnx {Command} {} hold @var{state}
## @deftypefnx {Function File} {} hold (@var{hax}, @dots{})
## Toggle or set the "hold" state of the plotting engine which determines
## whether new graphic objects are added to the plot or replace the existing
## objects.
##
## @table @code
## @item hold on
## Retain plot data and settings so that subsequent plot commands are displayed
## on a single graph.
##
## @item hold all
## Retain plot line color, line style, data and settings so that subsequent
## plot commands are displayed on a single graph with the next line color and
## style.
##
## @item hold off
## Clear plot and restore default graphics settings before each new plot
## command.  (default).
##
## @item hold
## Toggle the current hold state.
## @end table
##
## When given the additional argument @var{hax}, the hold state is modified
## only for the given axis handle.
##
## To query the current hold state use the @code{ishold} function.
## @seealso{ishold, cla, newplot, clf}
## @end deftypefn

function hold (varargin)

  if (nargin > 0 && numel (varargin{1}) == 1 && ishandle (varargin{1})
      && strcmp (get (varargin{1}, "type"), "axes"))
    [ax, varargin, nargs] = __plt_get_axis_arg__ ("hold", varargin{:});
    fig = get (ax, "parent");
  elseif (nargin > 0 && numel (varargin{1}) > 1 && ishandle (varargin{1}))
    print_usage ();
  else
    ax = gca ();
    fig = gcf ();
    nargs = numel (varargin);
  endif

  hold_all = false;
  if (nargs == 0)
    turn_hold_off = ishold (ax);
  elseif (nargs == 1)
    state = varargin{1};
    if (ischar (state))
      if (strcmpi (state, "off"))
        turn_hold_off = true;
      elseif (strcmpi (state, "all"))
        turn_hold_off = false;
        hold_all = true;
      elseif (strcmpi (state, "on"))
        turn_hold_off = false;
      else
        error ("hold: invalid hold STATE");
      endif
    endif
  else
    print_usage ();
  endif

  if (turn_hold_off)
    set (ax, "nextplot", "replace");
  else
    set (ax, "nextplot", "add");
    set (fig, "nextplot", "add");
  endif
  set (ax, "__hold_all__", hold_all);

endfunction


%!demo
%! clf;
%! A = rand (100);
%! [X, Y] = find (A > 0.9);
%! imshow (A);
%! hold on;
%! plot (X, Y, 'o');
%! hold off;

%!demo
%! clf;
%! colormap ('default');
%! hold on;
%! imagesc (1 ./ hilb (4));
%! plot (1:4, '-s');
%! hold off;

%!demo
%! clf;
%! colormap ('default');
%! hold on;
%! imagesc (1 ./ hilb (2));
%! imagesc (1 ./ hilb (4));
%! hold off;

%!demo
%! clf;
%! colormap ('default');
%! hold on;
%! plot (1:4, '-s');
%! imagesc (1 ./ hilb (4));
%! hold off;

%!demo
%! clf;
%! colormap ('default');
%! t = linspace (-3, 3, 50);
%! [x, y] = meshgrid (t, t);
%! z = peaks (x, y);
%! contourf (x, y, z, 10);
%! hold on;
%! plot (x(:), y(:), '^');
%! patch ([-1.0 1.0 1.0 -1.0 -1.0], [-1.0 -1.0 1.0 1.0 -1.0], 'red');
%! xlim ([-2.0 2.0]);
%! ylim ([-2.0 2.0]);
%! colorbar ('SouthOutside');
%! title ('Test script for some plot functions');

##hold on
%!test
%! hf = figure ("visible", "off");
%! unwind_protect
%!   p = plot ([0 1]);
%!   assert (! ishold);
%!   hold on;
%!   assert (ishold);
%!   p1 = fill ([0 1 1], [0 0 1], "black");
%!   p2 = fill ([0 1 0], [0 1 1], "red");
%!   assert (length (get (hf, "children")), 1);
%!   assert (length (get (gca, "children")), 3);
%! unwind_protect_cleanup
%!   close (hf);
%! end_unwind_protect

##hold off
%!test
%! hf = figure ("visible", "off");
%! unwind_protect
%!   p = plot ([0 1]);
%!   assert (! ishold);
%!   hold on;
%!   assert (ishold);
%!   p1 = fill ([0 1 1], [0 0 1], "black");
%!   hold off;
%!   p2 = fill ([0 1 0], [0 1 1], "red");
%!   assert (length (get (hf, "children")), 1);
%!   assert (length (get (gca, "children")), 1);
%! unwind_protect_cleanup
%!   close (hf);
%! end_unwind_protect