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#include "GuIntersectionEdgeEdge.h"
#include "GuInternal.h"

using namespace physx;

bool Gu::intersectEdgeEdge(const PxVec3& p1, const PxVec3& p2, const PxVec3& dir, const PxVec3& p3, const PxVec3& p4, PxReal& dist, PxVec3& ip)
{
	const PxVec3 v1 = p2 - p1;

	// Build plane P based on edge (p1, p2) and direction (dir)
	PxPlane plane;
	plane.n = v1.cross(dir);
	plane.d = -(plane.n.dot(p1));

	// if colliding edge (p3,p4) does not cross plane return no collision
	// same as if p3 and p4 on same side of plane return 0
	//
	// Derivation:
	// d3 = d(p3, P) = (p3 | plane.n) - plane.d;		Reversed sign compared to Plane::Distance() because plane.d is negated.
	// d4 = d(p4, P) = (p4 | plane.n) - plane.d;		Reversed sign compared to Plane::Distance() because plane.d is negated.
	// if d3 and d4 have the same sign, they're on the same side of the plane => no collision
	// We test both sides at the same time by only testing Sign(d3 * d4).
	// ### put that in the Plane class
	// ### also check that code in the triangle class that might be similar
	const PxReal d3 = plane.distance(p3);
	PxReal temp = d3 * plane.distance(p4);
	if(temp>0.0f)	return false;

	// if colliding edge (p3,p4) and plane are parallel return no collision
	PxVec3 v2 = p4 - p3;

	temp = plane.n.dot(v2);
	if(temp==0.0f)	return false;	// ### epsilon would be better

	// compute intersection point of plane and colliding edge (p3,p4)
	ip = p3-v2*(d3/temp);

	// find largest 2D plane projection
	PxU32 i,j;
	closestAxis(plane.n, i, j);

	// compute distance of intersection from line (ip, -dir) to line (p1,p2)
	dist =	(v1[i]*(ip[j]-p1[j])-v1[j]*(ip[i]-p1[i]))/(v1[i]*dir[j]-v1[j]*dir[i]);
	if(dist<0.0f)	return false;

	// compute intersection point on edge (p1,p2) line
	ip -= dist*dir;

	// check if intersection point (ip) is between edge (p1,p2) vertices
	temp = (p1.x-ip.x)*(p2.x-ip.x)+(p1.y-ip.y)*(p2.y-ip.y)+(p1.z-ip.z)*(p2.z-ip.z);
	if(temp<1e-3f)	return true;	// collision found

	return false;	// no collision
}
