quadrant.cpp

一个很好的vc底层代码

/**********************************************************************
 * $Id: Quadrant.cpp,v 1.2.2.1 2005/05/23 18:41:51 strk Exp $
 *
 * GEOS - Geometry Engine Open Source
 * http://geos.refractions.net
 *
 * Copyright (C) 2001-2002 Vivid Solutions Inc.
 *
 * This is free software; you can redistribute and/or modify it under
 * the terms of the GNU Lesser General Public Licence as published
 * by the Free Software Foundation. 
 * See the COPYING file for more information.
 *
 **********************************************************************
 * $Log: Quadrant.cpp,v $
 * Revision 1.2.2.1  2005/05/23 18:41:51  strk
 * Replaced sprintf uses with ostringstream
 *
 * Revision 1.2  2004/07/02 13:28:26  strk
 * Fixed all #include lines to reflect headers layout change.
 * Added client application build tips in README.
 *
 * Revision 1.1  2004/03/19 09:48:45  ybychkov
 * "geomgraph" and "geomgraph/indexl" upgraded to JTS 1.4
 *
 * Revision 1.10  2003/11/07 01:23:42  pramsey
 * Add standard CVS headers licence notices and copyrights to all cpp and h
 * files.
 *
 *
 **********************************************************************/


#include <sstream>
#include <geos/geomgraph.h>

namespace geos {

/**
* Returns the quadrant of a directed line segment (specified as x and y
* displacements, which cannot both be 0).
*/
int Quadrant::quadrant(double dx, double dy) {
	if (dx == 0.0 && dy == 0.0) {
		ostringstream s;
		s<<"Cannot compute the quadrant for point ";
		s<<"("<<dx<<","<<dy<<")"<<endl;
		throw new IllegalArgumentException(s.str());
	}
	if (dx >= 0) {
		if (dy >= 0)
			return 0;
		else
			return 3;
	} else {
		if (dy >= 0)
			return 1;
		else
		return 2;
	}
}

/**
* Returns the quadrant of a directed line segment from p0 to p1.
*/
int Quadrant::quadrant(const Coordinate& p0, const Coordinate& p1) {
	double dx=p1.x-p0.x;
	double dy=p1.y-p0.y;
	if (dx==0.0 && dy==0.0)
		throw new IllegalArgumentException("Cannot compute the quadrant for two identical points " + p0.toString());
	return quadrant(dx, dy);
}

/**
* Returns true if the quadrants are 1 and 3, or 2 and 4
*/
bool Quadrant::isOpposite(int quad1, int quad2){
	if (quad1==quad2) return false;
	int diff=(quad1-quad2+4)%4;
	// if quadrants are not adjacent, they are opposite
	if (diff==2) return true;
	return false;
}

/** 
* Returns the right-hand quadrant of the halfplane defined by the two quadrants,
* or -1 if the quadrants are opposite, or the quadrant if they are identical.
*/
int Quadrant::commonHalfPlane(int quad1, int quad2){
	// if quadrants are the same they do not determine a unique common halfplane.
	// Simply return one of the two possibilities
	if (quad1==quad2) return quad1;
	int diff=(quad1-quad2+4)%4;
	// if quadrants are not adjacent, they do not share a common halfplane
	if (diff==2) return -1;
	//
	int min=(quad1<quad2)? quad1:quad2;
	int max=(quad1>quad2)? quad1:quad2;
	// for this one case, the righthand plane is NOT the minimum index;
	if (min==0 && max==3) return 3;
	// in general, the halfplane index is the minimum of the two adjacent quadrants
	return min;
}

/**
* Returns whether the given quadrant lies within the given halfplane (specified
* by its right-hand quadrant).
*/
bool Quadrant::isInHalfPlane(int quad, int halfPlane){
	if (halfPlane==3) {
		return quad==3 || quad==0;
	}
	return quad==halfPlane || quad==halfPlane+1;
}

/**
* Returns true if the given quadrant is 0 or 1.
*/
bool Quadrant::isNorthern(int quad) {
	return quad==0 || quad==1;
}
}