File: 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 Library 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;
}