## Copyright (C) 2004-2016 David Legland <david.legland@grignon.inra.fr>
## Copyright (C) 2004-2016 INRA - CEPIA Nantes - MIAJ (Jouy-en-Josas)
## Copyright (C) 2016 Adapted to Octave by Juan Pablo Carbajal <ajuanpi+dev@gmail.com>
## All rights reserved.
##
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## modification, are permitted provided that the following conditions are met:
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## THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ''AS IS''
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%CLIPGRAPH Clip a graph with a rectangular area
%
%   [N2 E2] = clipGraph(N, E, BOX);
%   [N2 E2 F2] = clipGraph(N, E, F, BOX);
%   N is an array ov vertices, E an array of edges, containing indices of
%   first ans second vertices, and F (optional) is either a matrice or a
%   cell array containing indices of vertices for each face.
%   BOX is either a box given as a matrix: [XMIN XMAX;YMIN YMAX], or a row
%   vector following matlab axis format: [XMIN XMAX YMIN YMAX].
%
%   Example
%   clipGraph
%
%   See also
%   drawGraph, clipGraphPolygon
%

% ------
% Author: David Legland
% e-mail: david.legland@grignon.inra.fr
% Created: 2007-01-18
% Copyright 2007 INRA - BIA PV Nantes - MIAJ Jouy-en-Josas.

function varargout = clipGraph(nodes, edges, varargin)
  %% Format inputs

  % extract input arguments
  faces = [];
  if length(varargin)==1
      box     = varargin{1};
  elseif length(varargin)==2
      faces   = varargin{1};
      box     = varargin{2};
  else
      error('Wrong number of  arguments in clipGraph');
  end

  % uniformization of input for box.
  box = box';
  box = box(:);

  % accuracy of numeric computations
  ACC = eps;

  %% Get bounding lines

  % get bounds of the box
  xmin = box(1);
  xmax = box(2);
  ymin = box(3);
  ymax = box(4);

  % create box corners
  corners = [ ...
      xmin ymin; ...
      xmin ymax; ...
      xmax ymin; ...
      xmax ymax]; ...

  %% Clip the nodes

  % find nodes inside clipping window
  insideNodes = ...
      nodes(:,1)-xmin>ACC & nodes(:,1)-xmax<ACC & ...
      nodes(:,2)-ymin>ACC & nodes(:,2)-ymax<ACC;

  % convert to indices
  indNodes = find(insideNodes);

  % create correspondance between original nodes and inside nodes
  hashNodes = zeros(size(nodes, 1), 1);
  for i=1:length(indNodes)
      hashNodes(indNodes(i)) = i;
  end

  % select clipped nodes
  nodes2 = nodes(indNodes, :);

  %% Clip edges

  % initialize empty array
  edges2 = zeros([0 2]);

  % create correspondance map between old edges and clipped edges.
  hashEdges = zeros(size(edges, 1), 1);


  % iterate over each edge
  for e = 1:size(edges, 1)
      % current edge
      edge = [nodes(edges(e, 1), :) nodes(edges(e, 2), :)];

      % flags to indicate whether nodes are inside box or not
      in1 = ismember(edges(e, 1), indNodes);
      in2 = ismember(edges(e, 2), indNodes);

      % check if edge is totally inside window -> no clip
      if in1 && in2
          edges2 = [edges2; hashNodes(edges(e, :))']; %#ok<AGROW>
          hashEdges(e) = size(edges2, 1);
          continue;
      end

      % check that edge is not totally clipped -> no edge
      if edge(1)-xmin<ACC && edge(3)-xmin<ACC, continue; end
      if edge(1)-xmax>ACC && edge(3)-xmax>ACC, continue; end
      if edge(2)-ymin<ACC && edge(4)-ymin<ACC, continue; end
      if edge(2)-ymax>ACC && edge(4)-ymax>ACC, continue; end

      % otherwise, we have to clip the edge !
      edge = clipEdge(edge, [box(1) box(2); box(3) box(4)]);

      % display debug info
      %disp(sprintf('clip edge n°%2d, from %2d to %2d', e, edges(e,1), edges(e,2)));

      % Node for first vertex
      if ~in1
          nodes2 = [nodes2; edge([1 2])]; %#ok<AGROW>
          indN1 = size(nodes2, 1);
      else
          indN1 = hashNodes(edges(e, 1));
      end

      % Node for second vertex
      if ~in2
          nodes2 = [nodes2; edge([3 4])]; %#ok<AGROW>
          indN2 = size(nodes2, 1);
      else
          indN2 = hashNodes(edges(e, 2));
      end

      % add clipped edge to the list
      edges2 = [edges2; indN1 indN2]; %#ok<AGROW>
      hashEdges(e) = size(edges2, 1);
  end


  %% Clip the faces
  faces2 = {};
  for f = 1:length(faces)
      % indices of vertices of current face
      face = faces{f};

      % if the face is not clipped, use directly new indices of nodes
      face2 = hashNodes(face)';
      if ~ismember(0, face2)
          faces2 = [faces2, {face2}]; %#ok<AGROW>
          continue;
      end

      % At least one vertex is clipped. Here is some more special processing

      % edges of current face
      faceEdges = sort([face' face([2:end 1])'], 2);

      % indices of face edges in edges array
      indEdges = ismember(edges, faceEdges, 'rows');

      % convert to indices of edges in clipped edges array. indEdges with
      % value=0 correspond to totally clipped edges, and can be removed.
      indEdges = hashEdges(indEdges);
      indEdges = indEdges(indEdges~=0);

      % case of face totally clipped: break and continuue with next face
      if isempty(indEdges)
          continue;
      end

      % extract indices of vertices of the clipped face
      face2 = edges2(indEdges, :);
      face2 = unique(face2(:));

      % Test whether one should add one of the corner of the box.
      poly = [nodes(face, 1) nodes(face, 2)];
      ind = inpolygon(corners(:,1), corners(:,2), poly(:,1), poly(:,2));
      if sum(ind)>0
          nodes2 = [nodes2; corners(ind, :)]; %#ok<AGROW>
          face2 = [face2; size(nodes2, 1)]; %#ok<AGROW>
      end

      % vertices of the face, as points
      faceNodes = nodes2(face2, :);

      % sort vertices according to their angle around the centroid
      [faceNodes, I] = angleSort(faceNodes, centroid(faceNodes)); %#ok<ASGLU>

      % add current face to list of faces
      faces2 = [faces2, {face2(I)'}]; %#ok<AGROW>
  end


  %% Format output arguments

  % clean up nodes to ensure coord correspond to clipping box.
  nodes2(:,1) = min(max(nodes2(:,1), box(1)), box(2));
  nodes2(:,2) = min(max(nodes2(:,2), box(3)), box(4));

  if nargout==2
      varargout{1} = nodes2;
      varargout{2} = edges2;
  elseif nargout==3
      varargout{1} = nodes2;
      varargout{2} = edges2;
      varargout{3} = faces2;
  end

endfunction
