intline.m

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function [x,y] = intline(x1, x2, y1, y2)
%INTLINE Integer-coordinate line drawing algorithm.
%   [X, Y] = INTLINE(X1, X2, Y1, Y2) computes an
%   approximation to the line segment joining (X1, Y1) and
%   (X2, Y2) with integer coordinates.  X1, X2, Y1, and Y2
%   should be integers.  INTLINE is reversible; that is,
%   INTLINE(X1, X2, Y1, Y2) produces the same results as
%   FLIPUD(INTLINE(X2, X1, Y2, Y1)).

%   Steven L. Eddins, October 1994
%   Copyright 1993-1998 The MathWorks, Inc.  All Rights Reserved.
%   $Revision: 5.4 $  $Date: 1997/11/24 15:56:03 $

dx = abs(x2 - x1);
dy = abs(y2 - y1);

% Check for degenerate case.
if ((dx == 0) & (dy == 0))
  x = x1;
  y = y1;
  return;
end

flip = 0;
if (dx >= dy)
  if (x1 > x2)
    % Always "draw" from left to right.
    t = x1; x1 = x2; x2 = t;
    t = y1; y1 = y2; y2 = t;
    flip = 1;
  end
  m = (y2 - y1)/(x2 - x1);
  x = (x1:x2).';
  y = round(y1 + m*(x - x1));
else
  if (y1 > y2)
    % Always "draw" from bottom to top.
    t = x1; x1 = x2; x2 = t;
    t = y1; y1 = y2; y2 = t;
    flip = 1;
  end
  m = (x2 - x1)/(y2 - y1);
  y = (y1:y2).';
  x = round(x1 + m*(y - y1));
end
  
if (flip)
  x = flipud(x);
  y = flipud(y);
end