computeMeshEdges(faces)

function edges = computeMeshEdges(faces)
%COMPUTEMESHEDGES Computes edges array from face array
%
%   EDGES = computeMeshEdges(FACES);
%
%   Example
%   computeMeshEdges
%
%   See also
%   meshes3d
%
% ------
% Author: David Legland
% e-mail: [e-mail]
% Created: 2011-06-28,    using Matlab 7.9.0.529 (R2009b)
% Copyright 2011 INRA - Cepia Software Platform.

if ~iscell(faces)
    % faces is given as numeric array, 
    % all faces have same number of vertices, stored in nVF variable
    
    % compute total number of edges
    nFaces  = size(faces, 1);
    nVF     = size(faces, 2);
    nEdges  = nFaces * nVF;
    
    % create all edges (with double ones)
    edges = zeros(nEdges, 2);
    for i = 1:nFaces
        f = faces(i, :);
        edges(((i-1)*nVF+1):i*nVF, :) = [f' f([2:end 1])'];
    end
    
else
    % faces are given as a cell array, with possibly different number of
    % vertices
    nFaces  = length(faces);
    
    % compute number of edges
    nEdges = 0;
    for i = nFaces
        nEdges = nEdges + length(faces{i});
    end
    
    % allocate memory
    edges = zeros(nEdges, 2);
    ind = 0;
    
    % fillup edge array
    for i = 1:nFaces
        f = faces{i};
        nVF = length(f);
        edges(ind+1:ind+nVF, :) = [f' f([2:end 1])'];
        ind = ind + nVF;
    end
    
end

% keep only unique edges, and return sorted result
edges = sortrows(unique(sort(edges, 2), 'rows'));