function varargout = drawFaceNormals(varargin)
%DRAWFACENORMALS Draw normal vector of each face in a mesh
%
%   drawFaceNormals(V, E, F)
%   Compute and draw the face normals of the mesh defined by vertices V,
%   edges E and faces F. See meshes3d for format of each argument.
%
%   H = drawFaceNormals(...)
%   Return handle array to the created objects.
%
%   Example
%   % draw face normals of a cube
%     drawMesh(v, f)
%     axis([-1 2 -1 2 -1 2]);
%     hold on
%     drawFaceNormals(v, e, f)
%
%   See also
%   meshes3d, drawMesh, drawVector3d, quiver3
%

% ------
% Author: David Legland
% e-mail: david.legland@grignon.inra.fr
% Created: 2010-10-06,    using Matlab 7.9.0.529 (R2009b)
% Copyright 2010 INRA - Cepia Software Platform.

% extract vertices and faces
[vertices, faces] = parseMeshData(varargin{:});

% compute vector data
c = faceCentroids(vertices, faces);
n = faceNormal(vertices, faces);

% display an arrow for each normal
h = quiver3(c(:,1), c(:,2), c(:,3), n(:,1), n(:,2), n(:,3));

% format output
if nargout > 0
    varargout{1} = h;
end
