## Copyright (C) 2007-2018 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
## <https://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn  {} {} trisurf (@var{tri}, @var{x}, @var{y}, @var{z}, @var{c})
## @deftypefnx {} {} trisurf (@var{tri}, @var{x}, @var{y}, @var{z})
## @deftypefnx {} {} trisurf (@dots{}, @var{prop}, @var{val}, @dots{})
## @deftypefnx {} {@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 trisurf 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 @var{c}, which is a vector for colormap data, or a matrix with
## three columns for RGB data.  The number of colors specified in @var{c} must
## either equal the number of vertices in @var{z} or the number of triangles
## in @var{tri}.  When specifying the color at each vertex the triangle will
## be colored according to the color of the first vertex only (see patch
## documentation and the @qcode{"FaceColor"} property when set to
## @qcode{"flat"}).
##
## 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 < 4)
    print_usage ();
  endif

  if (nargin > 4 && isnumeric (varargin{1}))
    c = varargin{1};
    varargin(1) = [];
    if (isvector (c))
      c = c(:);
    end
    if (rows (c) != numel (z) && rows (c) != rows (tri))
      error ("trisurf: the numbers of colors specified in C must equal the number of vertices in Z or the number of triangles in TRI");
    elseif (columns (c) != 1 && columns (c) != 3)
      error ("trisurf: TrueColor C matrix must have 3 columns");
    endif
  else
    c = z(:);
  endif
  ## For Matlab compatibility:
  if (! any (strcmpi (varargin, "FaceColor")))
    varargin(end+(1:2)) = {"FaceColor", "flat"};
  endif

  hax = newplot ();

  htmp = patch ("Faces", tri, "Vertices", [x(:), y(:), z(:)],
                "FaceVertexCData", c, varargin{:});

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

  if (nargout > 0)
    h = htmp;
  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", "flat");
%! axis tight;
%! zlim auto;
%! title ({"trisurf() of peaks() function", 'facecolor = "flat"'});

%!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 ({"trisurf() of peaks() function", 'facecolor = "interp"'});

%!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(:));
%! title ("trisurf() of sparsely-sampled triangulation of peaks()");

%!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);
%! title ({"trisurf() of random data", 'default "facecolor" = "flat", "edgecolor" = "black"'});

%!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");
%! title ({"trisurf() of random data", '"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", "w");
%! title ({"trisurf() of random data", '"facecolor" = "interp", "edgecolor" = "white"'});

## Test input validation
%!error trisurf ()
%!error trisurf (1)
%!error trisurf (1,2)
%!error trisurf (1,2,3)
%!error <the numbers of colors> trisurf (1,2,3,4,[5 6])
%!error <the numbers of colors> trisurf (1,2,3,4,[5 6]')
%!error <the numbers of colors> trisurf ([1;1],[2;2],[3;3],[4;4], zeros (3,3))
%!error <TrueColor C matrix must have 3 columns>
%! trisurf ([1;1],[2;2],[3;3],[4;4], zeros (2,2))
