## Copyright (C) 2007-2012 David Bateman
##
## 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  {Function File} {} trisurf (@var{tri}, @var{x}, @var{y}, @var{z}, @var{c})
## @deftypefnx {Function File} {} trisurf (@var{tri}, @var{x}, @var{y}, @var{z})
## @deftypefnx {Function File} {} trisurf (@dots{}, @var{prop}, @var{val}, @dots{})
## @deftypefnx {Function File} {@var{h} =} trisurf (@dots{})
## Plot a 3-D triangular surface.
## 
## In contrast to @code{surf}, which plots a surface mesh using rectangles,
## @code{trisurf} plots the mesh using triangles.
##
## @var{tri} is typically the output of a Delaunay triangulation over the
## grid of @var{x}, @var{y}.  Every row of @var{tri} represents one triangle
## and contains three indices into [@var{x}, @var{y}] which are the
## vertices of the triangles in the x-y plane.  @var{z} determines the
## height above the plane of each vertex.
## 
## The color of the trimesh is computed by linearly scaling the @var{z} values
## to fit the range of the current colormap.  Use @code{caxis} and/or
## change the colormap to control the appearance.
##
## Optionally, the color of the mesh can be specified independently of @var{z}
## by supplying a color matrix, @var{c}.
##
## Any property/value pairs are passed directly to the underlying patch object.
##
## The optional return value @var{h} is a graphics handle to the created patch
## object.
## @seealso{surf, triplot, trimesh, delaunay, patch, shading}
## @end deftypefn

function h = trisurf (tri, x, y, z, varargin)

  if (nargin < 3)
    print_usage ();
  endif

  if (nargin == 3)
    triplot (tri, x, y);
  elseif (ischar (z))
    triplot (tri, x, y, z, varargin{:});
  else
    if (nargin > 4 && isnumeric (varargin{1}))
      c = varargin{1};
      varargin(1) = [];
    else
      c = z;
    endif
    if (! any (strcmpi (varargin, "FaceColor")))
      nfc = numel (varargin) + 1;
      varargin(nfc+(0:1)) = {"FaceColor", "flat"};
    else
      nfc = find (any (strcmpi (varargin, "FaceColor")), 1);
    endif
    if (! any (strcmpi (varargin, "EdgeColor"))
        && strcmpi (varargin{nfc+1}, "interp"))
      varargin(end+(1:2)) = {"EdgeColor", "none"};
    endif
    newplot ();
    handle = patch ("Faces", tri, "Vertices", [x(:), y(:), z(:)],
                    "FaceVertexCData", reshape (c, numel (c), 1),
                    varargin{:});
    if (nargout > 0)
      h = handle;
    endif

    if (! ishold ())
      set (gca (), "view", [-37.5, 30],
           "xgrid", "on", "ygrid", "on", "zgrid", "on");
    endif
  endif

endfunction


%!demo
%! clf;
%! colormap ('default');
%! N = 31;
%! [x, y] = meshgrid (1:N);
%! tri = delaunay (x(:), y(:));
%! z = peaks (N);
%! h = trisurf (tri, x, y, z, 'facecolor', 'interp');
%! axis tight;
%! zlim auto;
%! title (sprintf ('facecolor = %s', get (h, 'facecolor')));

%!demo
%! clf;
%! colormap ('default');
%! N = 31;
%! [x, y] = meshgrid (1:N);
%! tri = delaunay (x(:), y(:));
%! z = peaks (N);
%! h = trisurf (tri, x, y, z, 'facecolor', 'flat');
%! axis tight;
%! zlim auto;
%! title (sprintf ('facecolor = %s', get (h, 'facecolor')));

%!demo
%! clf;
%! colormap ('default');
%! old_state = rand ('state');
%! restore_state = onCleanup (@() rand ('state', old_state));
%! rand ('state', 10);
%! N = 10;
%! x = 3 - 6 * rand (N, N);
%! y = 3 - 6 * rand (N, N);
%! z = peaks (x, y);
%! tri = delaunay (x(:), y(:));
%! trisurf (tri, x(:), y(:), z(:));

%!demo
%! clf;
%! colormap ('default');
%! x = rand (100, 1);
%! y = rand (100, 1);
%! z = x.^2 + y.^2;
%! tri = delaunay (x, y);
%! trisurf (tri, x, y, z);

%!demo
%! clf;
%! colormap ('default');
%! x = rand (100, 1);
%! y = rand (100, 1);
%! z = x.^2 + y.^2;
%! tri = delaunay (x, y);
%! trisurf (tri, x, y, z, 'facecolor', 'interp');

%!demo
%! clf;
%! colormap ('default');
%! x = rand (100, 1);
%! y = rand (100, 1);
%! z = x.^2 + y.^2;
%! tri = delaunay (x, y);
%! trisurf (tri, x, y, z, 'facecolor', 'interp', 'edgecolor', 'k');