dir.cc

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/*
 *  dir.cc - Directions.
 *
 *  Copyright (C) 1998-1999  Jeffrey S. Freedman
 *  Copyright (C) 2000-2001  The Exult Team
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include "dir.h"

/*
 *  Return the direction for a given slope (0-7).
 *  NOTE:  Assumes cartesian coords, NOT screen coords. (which have y
 *    growing downwards).
 */

Direction Get_direction
  (
  int deltay,
  int deltax
  )
{
  if (deltax == 0)
    return deltay > 0 ? north : south;
  int dydx = (1024*deltay)/deltax;// Figure 1024*tan.
  if (dydx >= 0)
    if (deltax >= 0)  // Top-right quadrant?
      return dydx <= 424 ? east : dydx <= 2472 ? northeast
                : north;
    else      // Lower-left.
      return dydx <= 424 ? west : dydx <= 2472 ? southwest
                : south;
  else
    if (deltax >= 0)  // Lower-right.
      return dydx >= -424 ? east : dydx >= -2472 ? southeast
                : south;
    else      // Top-left?
      return dydx >= -424 ? west : dydx >= -2472 ? northwest
                : north;
}

/*
 *  Return the direction for a given slope (0-7), rounded to NSEW.
 *  NOTE:  Assumes cartesian coords, NOT screen coords. (which have y
 *    growing downwards).
 */

Direction Get_direction4
  (
  int deltay,
  int deltax
  )
{
  if (deltax >= 0)    // Right side?
    return (deltay > deltax ? north : deltay < -deltax ? south
                : east);
  else        // Left side.
    return (deltay > -deltax ? north : deltay < deltax ? south
                : west);
}

/*
 *  Return the direction for a given slope (0-15).
 *  NOTE:  Assumes cartesian coords, NOT screen coords. (which have y
 *    growing downwards).
 */

int Get_direction16
  (
  int deltay,
  int deltax
  )
{
  if (deltax == 0)
    return deltay > 0 ? 0 : 8;
  int dydx = (1024*deltay)/deltax;// Figure 1024*tan.
  int adydx = dydx < 0 ? -dydx : dydx;
  int angle = 0;
  if (adydx < 1533)   // 1024*tan(5*11.25)
  {
    if (adydx < 204)  // 1024*tan(11.25).
      angle = 4;
    else if (adydx < 684) // 1024*tan(3*11.25).
      angle = 3;
    else
      angle = 2;
  }
  else
  {
    if (adydx < 5148) // 1024*tan(7*11.25).
      angle = 1;
    else
      angle = 0;
  }

  if (deltay < 0)     // Check quadrants.
    if (deltax > 0)
      angle = 8 - angle;
    else
      angle += 8;
  else if (deltax < 0)
    angle = 16 - angle;
  return angle % 16;
}

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