Figure 6: Class Triangle

// **********************************************************
//   File: Triangle.h
//   Description: Definition of class Triangle
//
//   Author: Carlos Moreno
// **********************************************************

#ifndef __TRIANGLE_H__
#define __TRIANGLE_H__

#include "Point.h"

const int left_turn = +1;
const int right_turn = -1;
const int collinear = 0;

const int counter_clockwise = left_turn;
const int clockwise = right_turn;


class Triangle  
{
public:

        //Constructor
    explicit Triangle (const Point & p1 = origin, 
                 const Point & p2 = origin, 
                 const Point & p3 = origin)
        : v1 (p1), v2 (p2), v3 (p3) {}

        // Geometric and miscelaneous operations
    void draw () const;

    bool contains (const Point &) const;
    double area () const;
    int orientation () const;

        // Comparison operators
    bool operator== (const Triangle & t) const;
    bool operator!= (const Triangle & t) const;

    bool operator> (const Triangle &) const;
    bool operator< (const Triangle &) const;

private:
    Point v1, v2, v3;

    double signed_area () const;
};


inline int turn (const Point & p1, const Point & p2, 
    const Point & p3)
{
    return Triangle(p1,p2,p3).orientation();
}

#endif

// **********************************************************
//   File: Triangle.cpp
//   Description: Implementation of class Triangle
//
//   Author: Carlos Moreno
// **********************************************************

#include "Triangle.h"
#include "Segment.h"

#include <math.h>


double Triangle::signed_area () const
{
    return (v1.get_x() * (v2.get_y() - v3.get_y()) +
        v2.get_x() * (v3.get_y() - v1.get_y()) +
        v3.get_x() * (v1.get_y() - v2.get_y()));
}


bool Triangle::contains (const Point & p) const
{
    return turn (v1,v2,p) == turn (v2,v3,p) &&
           turn (v2,v3,p) == turn (v3,v1,p);
}


void Triangle::draw () const
{
    Segment (v1,v2).draw();
    Segment (v2,v3).draw();
    Segment (v1,v3).draw();
}


double Triangle::area () const
{
    return fabs (signed_area());
}


int Triangle::orientation () const
{
    double s_a = signed_area();

    return s_a > 0 ? 1 : (s_a < 0 ? -1 : 0);
}


bool Triangle::operator== (const Triangle & t) const
{
    return v1 == t.v1 && v2 == t.v2 && v3 == t.v3;
}


bool Triangle::operator!= (const Triangle & t) const
{
    return !(*this == t);
}
//End of File