%% Copyright (c) 2011, INRA
%% 2004-2011, David Legland <david.legland@grignon.inra.fr>
%% 2011 Adapted to Octave by Juan Pablo Carbajal <carbajal@ifi.uzh.ch>
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%% -*- texinfo -*-
%% @deftypefn {Function File} {@var{alpha} =} angle3Points (@var{p1}, @var{p2}, @var{p3})
%% Computes the angle between the points @var{p1}, @var{p2} and @var{p3}.
%%
%% @var{p1}, @var{p2} and @var{p3} are either [1x2] arrays, or [Nx2] arrays, in this case
%% @var{alpha} is a [Nx1] array. The angle computed is the directed angle between line 
%% (@var{p2}@var{p1}) and line (@var{p2}@var{p3}).
%%
%% Result is always given in radians, between 0 and 2*pi.
%% 
%% @seealso{points2d, angles2d, angle2points}
%% @end deftypefn

function theta = angle3Points(varargin)

  if length(varargin)==3
      p1 = varargin{1};
      p2 = varargin{2};
      p3 = varargin{3};
  elseif length(varargin)==1
      var = varargin{1};
      p1 = var(1,:);
      p2 = var(2,:);
      p3 = var(3,:);
  end

  % angle line (P2 P1)
  theta = lineAngle(createLine(p2, p1), createLine(p2, p3));

endfunction

%!test
%! % all points inside window, possibly touching edges
%! p1 = [10 0];
%! p2 = [0 0];
%! p3 = [0 10];
%! angle_ = angle3Points(p1, p2, p3);
%! assert(pi/2, angle_,1e-6);
%! angle_ = angle3Points([p1; p2; p3]);
%! assert(pi/2, angle_, 1e-6);

%!test
%! p1 = [10 0; 20 0];
%! p2 = [0 0;0 0];
%! p3 = [0 10; 0 20];
%! angle_ = angle3Points(p1, p2, p3);
%! assert(2, size(angle_, 1));
%! assert([pi/2;pi/2], angle_, 1e-6);