bool PointProjectionTools::segmentIntersect(const CCVector2& A, const CCVector2& B, const CCVector2& C, const CCVector2& D)
{
CCVector2 AB = B-A;
CCVector2 AC = C-A;
CCVector2 AD = D-A;
PointCoordinateType cross_AB_AC = AB.cross(AC);
PointCoordinateType cross_AB_AD = AB.cross(AD);
//both C and D are on the same side of AB?
if (cross_AB_AC * cross_AB_AD > 0)
{
//no intersection
return false;
}
CCVector2 CD = D-C;
CCVector2 CB = B-C;
PointCoordinateType cross_CD_CA = -CD.cross(AC);
PointCoordinateType cross_CD_CB = CD.cross(CB);
//both A and B are on the same side of CD?
if (cross_CD_CA * cross_CD_CB > 0)
{
//no intersection
return false;
}
PointCoordinateType cross_AB_CD = AB.cross(CD);
if (fabs(cross_AB_CD) != 0) //AB and CD are not parallel
{
//where do they intersect?
//PointCoordinateType v = cross_AB_AC/cross_AB_CD;
//assert(v >= 0 && v <= 1);
return true;
}
else //AB and CD are parallel (therefore they are colinear - see above tests)
{
PointCoordinateType dAB = AB.norm();
PointCoordinateType dot_AB_AC = AB.dot(AC);
if (dot_AB_AC >= 0 && dot_AB_AC < dAB * AC.norm())
{
//C is between A and B
return true;
}
PointCoordinateType dot_AB_AD = AB.dot(AD);
if (dot_AB_AD >= 0 && dot_AB_AD < dAB * AD.norm())
{
//D is between A and B
return true;
}
//otherwise there's an intersection only if B and C are on both sides!
return (dot_AB_AC * dot_AB_AD < 0);
}
}
//! Returns true if the AB and CD segments intersect each other
bool Intersect(const CCVector2& A, const CCVector2& B, const CCVector2& C, const CCVector2& D)
{
if (cross(A,B,C) * cross(A,B,D) >= 0) //both points are on the same side? No intersection
return false;
CCVector2 AB = B-A;
CCVector2 AC = C-A;
CCVector2 CD = D-C;
PointCoordinateType q = CD.y * AB.x - CD.x * AB.y;
if (fabs(q) > ZERO_TOLERANCE) //AB and CD are not parallel
{
//where do they interest?
PointCoordinateType p = AC.x * AB.y - AC.y * AB.x;
PointCoordinateType v = p/q;
if (v <= 0 || v >= 1) //not CD!
return false;
//test further with AB
p = CD.y * AC.x - CD.x * AC.y;
v= p/q;
return (v > 0 && v < 1); //not AB?
}
else //AB and CD are parallel
{
PointCoordinateType dAB = AB.norm();
PointCoordinateType dAC = AC.norm();
PointCoordinateType dot = AB.dot(AC) / (dAB * dAC);
if (fabs(dot) < 0.999)
{
//not colinear
return false;
}
else
{
//colinear --> do they actually intersect?
return (dAC < dAB || (D-A).norm() < dAB);
}
}
}
