point.cpp revision c8589a6c7367d09fa756755cef0dd448c7328a71
/**
* \file
* \brief Cartesian point / 2D vector and related operations
*//*
* Authors:
* Michael G. Sloan <mgsloan@gmail.com>
* Nathan Hurst <njh@njhurst.com>
* Krzysztof Kosiński <tweenk.pl@gmail.com>
*
* Copyright (C) 2006-2009 Authors
*
* This library is free software; you can redistribute it and/or
* modify it either under the terms of the GNU Lesser General Public
* License version 2.1 as published by the Free Software Foundation
* (the "LGPL") or, at your option, under the terms of the Mozilla
* Public License Version 1.1 (the "MPL"). If you do not alter this
* notice, a recipient may use your version of this file under either
* the MPL or the LGPL.
*
* You should have received a copy of the LGPL along with this library
* in the file COPYING-LGPL-2.1; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
* You should have received a copy of the MPL along with this library
* in the file COPYING-MPL-1.1
*
* The contents of this file are subject to the Mozilla Public License
* Version 1.1 (the "License"); you may not use this file except in
* compliance with the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY
* OF ANY KIND, either express or implied. See the LGPL or the MPL for
* the specific language governing rights and limitations.
*/
#include <assert.h>
#include <math.h>
#include <2geom/point.h>
#include <2geom/transforms.h>
namespace Geom {
/**
* @class Point
* @brief Two-dimensional point that doubles as a vector.
*
* Points in 2Geom are represented in Cartesian coordinates, e.g. as a pair of numbers
* that store the X and Y coordinates. Each point is also a vector in \f$\mathbb{R}^2\f$
* from the origin (point at 0,0) to the stored coordinates,
* and has methods implementing several vector operations (like length()).
*
* @section OpNotePoint Operator note
*
* Most operators are provided by Boost operator helpers, so they are not visible in this class.
* If @a p, @a q, @a r denote points, @a s a floating-point scalar, and @a m a transformation matrix,
* then the following operations are available:
* @code
p += q; p -= q; r = p + q; r = p - q;
p *= s; p /= s; q = p * s; q = s * p; q = p / s;
p *= m; q = p * m; q = m * p;
@endcode
* It is possible to left-multiply a point by a matrix, even though mathematically speaking
* this is undefined. The result is a point identical to that obtained by right-multiplying.
*
* @ingroup Primitives */
/** @brief Normalize the vector representing the point.
* After this method returns, the length of the vector will be 1 (unless both coordinates are
* zero - the zero point will be returned then). The function tries to handle infinite
* coordinates gracefully. If any of the coordinates are NaN, the function will do nothing.
* @post \f$-\epsilon < \left|this\right| - 1 < \epsilon\f$
* @see unit_vector(Geom::Point const &) */
void Point::normalize() {
double len = hypot(_pt[0], _pt[1]);
if(len == 0) return;
if(IS_NAN(len)) return;
static double const inf = HUGE_VAL;
if(len != inf) {
*this /= len;
} else {
unsigned n_inf_coords = 0;
/* Delay updating pt in case neither coord is infinite. */
Point tmp;
for ( unsigned i = 0 ; i < 2 ; ++i ) {
if ( _pt[i] == inf ) {
++n_inf_coords;
tmp[i] = 1.0;
} else if ( _pt[i] == -inf ) {
++n_inf_coords;
tmp[i] = -1.0;
} else {
tmp[i] = 0.0;
}
}
switch (n_inf_coords) {
case 0: {
/* Can happen if both coords are near +/-DBL_MAX. */
*this /= 4.0;
len = hypot(_pt[0], _pt[1]);
assert(len != inf);
*this /= len;
break;
}
case 1: {
*this = tmp;
break;
}
case 2: {
*this = tmp * sqrt(0.5);
break;
}
}
}
}
/** @brief Compute the first norm (Manhattan distance) of @a p.
* This is equal to the sum of absolutes values of the coordinates.
* @return \f$|p_X| + |p_Y|\f$
* @relates Point */
Coord L1(Point const &p) {
Coord d = 0;
for ( int i = 0 ; i < 2 ; i++ ) {
d += fabs(p[i]);
}
return d;
}
/** @brief Compute the infinity norm (maximum norm) of @a p.
* @return \f$\max(|p_X|, |p_Y|)\f$
* @relates Point */
Coord LInfty(Point const &p) {
Coord const a(fabs(p[0]));
Coord const b(fabs(p[1]));
return ( a < b || IS_NAN(b)
? b
: a );
}
/** @brief True if the point has both coordinates zero.
* NaNs are treated as not equal to zero.
* @relates Point */
bool is_zero(Point const &p) {
return ( p[0] == 0 &&
p[1] == 0 );
}
/** @brief True if the point has a length near 1. The are_near() function is used.
* @relates Point */
bool is_unit_vector(Point const &p) {
return are_near(L2(p), 1.0);
}
/** @brief Return the angle between the point and the +X axis.
* @return Angle in \f$(-\pi, \pi]\f$.
* @relates Point */
Coord atan2(Point const &p) {
return std::atan2(p[Y], p[X]);
}
/** @brief Compute the angle between a and b relative to the origin.
* The computation is done by projecting b onto the basis defined by a, rot90(a).
* @return Angle in \f$(-\pi, \pi]\f$.
* @relates Point */
Coord angle_between(Point const &a, Point const &b) {
return std::atan2(cross(b,a), dot(b,a));
}
/** @brief Create a normalized version of a point.
* This is equivalent to copying the point and calling its normalize() method.
* The returned point will be (0,0) if the argument has both coordinates equal to zero.
* If any coordinate is NaN, this function will do nothing.
* @param a Input point
* @return Point on the unit circle in the same direction from origin as a, or the origin
* if a has both coordinates equal to zero
* @relates Point */
Point unit_vector(Point const &a)
{
Point ret(a);
ret.normalize();
return ret;
}
/** @brief Return the "absolute value" of the point's vector.
* This is defined in terms of the default lexicographical ordering. If the point is "larger"
* that the origin (0, 0), its negation is returned. You can check whether
* the points' vectors have the same direction (e.g. lie
* on the same line passing through the origin) using
* @code abs(a).normalize() == abs(b).normalize() @endcode
* To check with some margin of error, use
* @code are_near(abs(a).normalize(), abs(b).normalize()) @endcode
* Although naively this should take the absolute value of each coordinate, such an operation
* is not very useful.
* @relates Point */
Point abs(Point const &b)
{
Point ret;
if (b[Y] < 0.0) {
ret = -b;
} else if (b[Y] == 0.0) {
ret = b[X] < 0.0 ? -b : b;
} else {
ret = b;
}
return ret;
}
/** @brief Transform the point by the specified matrix. */
Point &Point::operator*=(Affine const &m) {
double x = _pt[X], y = _pt[Y];
for(int i = 0; i < 2; i++) {
_pt[i] = x * m[i] + y * m[i + 2] + m[i + 4];
}
return *this;
}
/** @brief Snap the angle B - A - dir to multiples of \f$2\pi/n\f$.
* The 'dir' argument must be normalized (have unit length), otherwise the result
* is undefined.
* @return Point with the same distance from A as B, with a snapped angle.
* @post distance(A, B) == distance(A, result)
* @post angle_between(result - A, dir) == \f$2k\pi/n, k \in \mathbb{N}\f$
* @relates Point */
Point constrain_angle(Point const &A, Point const &B, unsigned int n, Point const &dir)
{
// for special cases we could perhaps use explicit testing (which might be faster)
if (n == 0.0) {
return B;
}
Point diff(B - A);
double angle = -angle_between(diff, dir);
double k = round(angle * (double)n / (2.0*M_PI));
return A + dir * Rotate(k * 2.0 * M_PI / (double)n) * L2(diff);
}
} // end namespace Geom
/*
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*/
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