fuckme.c++

template <typename T>
optional<THit3<T>> intersect( const TRay3<T>& ray, const RTriangle3<T>& target, bool singlesided = false ) {
	
	THit3<T> hit;
	RVector3<T> edgeb = target.b - target.a;
	RVector3<T> edgec = target.c - target.a;
	RVector3<T> nperpendicular = cross( edgec, ray.direction );
	T determinant = dot( edgeb, nperpendicular );
	if ( determinant == static_cast<T>( 0 ) || ( singlesided && ( determinant > static_cast<T>( 0 ) ) ) )
		return nullopt;
	
	RVector3<T> atoorigin = ray.origin - target.a;
	T u = dot( atoorigin, nperpendicular ) / determinant;
	if ( u < static_cast<T>( 0 ) || u > static_cast<T>( 1 ) )
		return nullopt;
	
	RVector3<T> originedgecross = cross( atoorigin, edgeb );
	T v = dot( ray.direction, originedgecross ) / determinant;
	if ( v < static_cast<T>( 0 ) || v > static_cast<T>( 1 ) )
		return nullopt;
	
	hit.distance0 = hit.distance1 = dot( edgec, originedgecross ) / determinant;
	if ( !( hit.distance0 > static_cast<T>( 0 ) ) )
		return nullopt;
	
	hit.contact = ray.at( hit.distance0 );
	hit.stu.s = u;
	hit.stu.t = v;
	hit.inside = false;
	return std::move( hit );
}

test.c++

void testhit( Ray3 ray, Triangle3 triangle ) {
	auto hit = intersect( ray, triangle );
	std::cout << ( hit ? "Hit!" : "Sad." ) << std::endl;
}

int main( ) {
	Triangle3 triangle( 
		Vector3{ 0, 0, 0 },
		Vector3{ 0, 4, 0 },
		Vector3{ 4, 0, 0 } );

	Vector3 dir0( 0, 0, 1 );
	testhit( { Vector3( 4, 4, -30 ), dir0 }, triangle );
	testhit( { Vector3( 1, 1, -30 ), dir0 }, triangle );
	testhit( { Vector3( 0, 0, -30 ), dir0 }, triangle );
	testhit( { Vector3( -1, 0, -30 ), dir0 }, triangle );
	testhit( { Vector3( 0, -1, -30 ), dir0 }, triangle );
}