secondo/Algebras/RegionInterpolation2/librip/devel/Pt.cpp

/*
 1 Class Pt represents a single point.

*/

#include "interpolate.h"

Pt::Pt() : valid(0) {
}

Pt::Pt(double x, double y) : x(x), y(y), valid(1) {
}

/*
 1.1 ~less-operator~ sorts by y-value as first criterion, then by x-value
 
*/
bool Pt::operator<(const Pt& a) const {
    return ((y < a.y) || ((y == a.y) && (x < a.x)));
}

/*
 1.1 ~equality-operator~: Two points are equal if their x- and y-coordinates match
 
*/
bool Pt::operator==(const Pt& a) const {
    return (x == a.x && y == a.y);
}

/*
 1.2a ~minus-operator~ calculates the x- and y-offset of two points.
 
*/
Pt Pt::operator-(const Pt& a) const {
    return Pt(x-a.x,y-a.y);
}

/*
 1.2b ~unary-minus-operator~ negates the coordinates.
 
*/
Pt Pt::operator-() const {
    return Pt(-x,-y);
}

/*
 1.3 ~plus-operator~ returns the point which is composed from the sum of the
 coordinates of the two points to be added.
 
*/
Pt Pt::operator+(const Pt& a) const {
    return Pt(x+a.x,y+a.y);
}

/*
 1.4 ~divide-operator~ divides both coordinates by a scale factor
 
*/
Pt Pt::operator/(const double a) const {
    return Pt(x/a,y/a);
}

/*
 1.5 ~multiply-operator~ multiplies both coordinates by a scale factor
 
*/
Pt Pt::operator*(const Pt& a) const {
    return Pt(x*a.x,y*a.y);
}

// Helper-function to sort the points by their (pre-calculated) polar
// coordinates. If the angle is equal, then sort by descending (!) distance
bool Pt::lessPolar(const Pt& a) const {
    return ((angle < a.angle) || ((angle == a.angle) && (dist > a.dist))) ;
}

/*
  1.6 ~calcPolar~ calculates the polar coordinates of this point relative to
  the origin ~origin~. This sets the attributes ~angle~ and ~distance~ of this
  object.
 
*/
void Pt::calcPolar(const Pt& origin) {
    long double tmpx = x - origin.x;
    long double tmpy = y - origin.y;

    long double tmp = (tmpy != 0) ? tmpy/tmpx : 0;
    if (tmpx > 0) {
        angle = atan(tmp);
    } else if (tmpx < 0 && tmpy >= 0) {
        angle = atan(tmp)+M_PI;
    } else if (tmpx < 0 && tmpy < 0) {
        angle = atan(tmp)-M_PI;
    } else if (tmpx == 0 && tmpy > 0) {
        angle = M_PI/2;
    } else if (tmpx == 0 && tmpy < 0) {
        angle = -M_PI/2;
    } else {
        angle = -5;
    }
    
//    angle = acos(tmpx / hyp);
    dist = sqrt(tmpx * tmpx + tmpy * tmpy);
}

/*
  1.7 ~ToString~ returns a string-representation of this object
 
*/
string Pt::ToString() const {
    std::ostringstream ss;
    ss << "(" << x << "/" << y << ")";
    return ss.str();
}

/*
 1.8 ~sign~ determines the relationship of the three points a, b and c.
 If the result is
 * positive, then the point a is left of (b c)
 * zero, then the points are collinear
 * negative, then the point a is right of (b c)
 
*/
double Pt::sign(const Pt& a, const Pt& b, const Pt& c) {

         return ((a.x-c.x)*(b.y-c.y)-(a.y-c.y)*(b.x-c.x));
}

/*
 1.9 ~insideTriangle~ checks, if the point x is inside the triangle (a b c).
 This is exactly the case, if the point x is on the same side of all three
 triangle-segments (a b), (b c) and (c a).
 * left,  when the triangle (a b c) is counterclockwise oriented)
 * right, when the triangle (a b c) is clockwise oriented)
 
*/
bool Pt::insideTriangle(const Pt& a, const Pt& b, const Pt& c, const Pt& x) {
    bool b1, b2, b3;
    
    b1 = Pt::sign(x, a, b) < 0;
    b2 = Pt::sign(x, b, c) < 0;
    b3 = Pt::sign(x, c, a) < 0;
    
    return ((b1 == b2) && (b2 == b3));
}

/*
 1.10 ~distance~ calculates the distance between this point and ~p~ using
 pythagoras' formula.
 
*/
double Pt::distance(Pt p) {
    return sqrt((p.x-x)*(p.x-x)+(p.y-y)*(p.y-y));
}