########################################################################
##
## Copyright (C) 1993-2026 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## 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.
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## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
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## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING.  If not, see
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########################################################################

## -*- texinfo -*-
## @deftypefn  {} {} contour (@var{z})
## @deftypefnx {} {} contour (@var{z}, @var{vn})
## @deftypefnx {} {} contour (@var{x}, @var{y}, @var{z})
## @deftypefnx {} {} contour (@var{x}, @var{y}, @var{z}, @var{vn})
## @deftypefnx {} {} contour (@dots{}, @var{style})
## @deftypefnx {} {} contour (@var{hax}, @dots{})
## @deftypefnx {} {[@var{c}, @var{h}] =} contour (@dots{})
## Create a 2-D contour plot.
##
## Plot level curves (contour lines) of the matrix @var{z}, using the
## contour matrix @var{c} computed by @code{contourc} from the same
## arguments; see the latter for their interpretation.
##
## The appearance of contour lines can be defined with a line style @var{style}
## in the same manner as @code{plot}.  Only line style and color are used;
## Any markers defined by @var{style} are ignored.
##
## If the first argument @var{hax} is an axes handle, then plot into this axes,
## rather than the current axes returned by @code{gca}.
##
## The optional output @var{c} contains the contour levels in @code{contourc}
## format.
##
## The optional return value @var{h} is a graphics handle to the hggroup
## comprising the contour lines.
##
## Example:
##
## @example
## @group
## x = 0:3;
## y = 0:2;
## z = y' * x;
## contour (x, y, z, 2:3)
## @end group
## @end example
##
## @seealso{ezcontour, contourc, contourf, contour3, clabel, meshc, surfc,
## clim, colormap, plot}
##
## @end deftypefn

function [c, h] = contour (varargin)

  [hax, varargin] = __plt_get_axis_arg__ ("contour", varargin{:});

  hax = newplot (hax);

  [ctmp, htmp] = __contour__ (hax, "none", varargin{:});

  if (! ishold (hax))
    set (hax, "box", "on");
  endif

  if (nargout > 0)
    c = ctmp;
    h = htmp;
  endif

endfunction


%!demo
%! clf;
%! colormap ("default");
%! [x, y, z] = peaks ();
%! contour (x, y, z);
%! title ({"contour() plot (isolines of constant Z)"; "Z = peaks()"});

%!demo
%! clf;
%! colormap ("default");
%! [theta, r] = meshgrid (linspace (0,2*pi,64), linspace (0,1,64));
%! [X, Y] = pol2cart (theta, r);
%! Z = sin (2*theta) .* (1-r);
%! contour (X, Y, abs (Z), 10);
%! title ({"contour() plot"; "polar fcn: Z = sin (2*theta) * (1-r)"});

%!demo
%! clf;
%! colormap ("default");
%! z = peaks ();
%! contour (z, [0 0]);
%! title ({"contour() plot with single isoline at Z == 0"; "Z = peaks()"});

%!test
%! hf = figure ("visible", "off");
%! clf (hf);
%! unwind_protect
%!   [x, y, z] = peaks ();
%!   [c, h] = contour (x, y, z);
%!   levellist = -6:6;
%!   set (h, "levellist", levellist);
%!   assert (get (h, "levellist"), levellist);
%!   assert (get (h, "levellistmode"), "manual");
%! unwind_protect_cleanup
%!   close (hf);
%! end_unwind_protect

%!test
%! hf = figure ("visible", "off");
%! clf (hf);
%! unwind_protect
%!   [x, y, z] = peaks ();
%!   [c, h] = contour (x, y, z);
%!   levelstep = 3;
%!   set (h, "levelstep", levelstep);
%!   assert (get (h, "levelstep"), levelstep);
%!   assert (get (h, "levelstepmode"), "manual");
%!   assert (get (h, "levellist"), -6:levelstep:6);
%!   assert (get (h, "levellistmode"), "auto");
%! unwind_protect_cleanup
%!   close (hf);
%! end_unwind_protect
