intelliphoto/Abgabe/Abgabe 4/Painting/IntelliHelper/IntelliHelper.cpp

#include"IntelliHelper.h"
#include<algorithm>

int IntelliHelper::orientation(QPoint& p,  QPoint& q, QPoint& r){
    int value = (q.y()-p.y())*(r.x()-q.x())-
                (q.x()-p.x())*(r.y()-q.y());
    if(value==0) return 0;
    return (value>0)?1:2;
}

bool IntelliHelper::onSegment(QPoint& p1, QPoint& q, QPoint& p2){
    return (q.x() >= std::min(p1.x(),p2.x()) && q.x() <= std::max(p1.x(), p2.x()) &&
            q.y() >= std::min(p1.y(),p2.y()) && q.y() <= std::max(p1.y(), p2.y()));
}

bool IntelliHelper::hasIntersection(QPoint& p1, QPoint& q1, QPoint& p2, QPoint& q2){
    int o1 = IntelliHelper::orientation(p1,q1,p2);
    int o2 = IntelliHelper::orientation(p1,q1,q2);
    int o3 = IntelliHelper::orientation(p2,q2,p1);
    int o4 = IntelliHelper::orientation(p2,q2,q1);

    // General case
    if (o1 != o2 && o3 != o4)
        return true;

    // p1, q1 and p2 are colinear and p2 lies on segment p1q1
    if (o1 == 0 && onSegment(p1, p2, q1)) return true;

    // p1, q1 and q2 are colinear and q2 lies on segment p1q1
    if (o2 == 0 && onSegment(p1, q2, q1)) return true;

    // p2, q2 and p1 are colinear and p1 lies on segment p2q2
    if (o3 == 0 && onSegment(p2, p1, q2)) return true;

     // p2, q2 and q1 are colinear and q1 lies on segment p2q2
    if (o4 == 0 && onSegment(p2, q1, q2)) return true;

    return false; // Doesn't fall in any of the above cases
}