Point in triangle test

pointInTriangle.cpp

struct Vector2
{
	double x;
	double y;
};
	
struct Triangle2
{
	Vector2 v[3];
};

double signedArea(const Vector2& apex, const Vector2& p1, const Vector2& p2)
{
	return (p1.x - apex.x) * (p2.y - apex.y) - (p1.y - apex.y) * (p2.x - apex.y);
};

bool contains(const Triangle2& t, const Vector2& p, double precision = 0.00001)
{
	//e0 is the triangle's edge from its first to its second vertex.
	//e1 is the triangle's edge from its second to its third vertex.
	//e2 is the triangle's edge from its third to its first vertex.
	double sign0 = signedArea(t.v[0],t.v[1],p);
	double sign1 = signedArea(t.v[1],t.v[2],p);
	if (sign0 > precision)
	{
		if (sign1 < -precision)
		{
			return false; // right of e0, left of e1
		}
		else
		{
			double sign2 = signedArea(t.v[2],t.v[0],p);
			if (sign2 < -precision)
			{
				return false; // right of e0, right of/aligned with e1, left of e2
			}
			else
			{
				return true; // right of e0, right of/aligned with e1, right of/aligned with e2 
			}
		}
	}
	else if (sign0 < -precision)
	{
		if (sign1 > precision)
		{
			return false; // left of e0, right of e1
		}
		else
		{
			double sign2 = signedArea(t.v[2],t.v[0],p);
			if (sign2 > precision)
			{
				return false; // left of e0, left of/aligned with e1, right of e2
			}
			else
			{
				return true; // left of e0, left of/aligned with e1, right of/aligned with e2 
			}
		}
	}
	else
	{
		double sign2 = signedArea(t.v[2],t.v[0],p);
		if (sign1 > precision)
		{
			if (sign2 < -precision)
			{
				return false; // aligned with e0, right of e1, left of e2
			}
			else
			{
				return true; // aligned with e0, right of e1, right of/aligned with e2
			}
		}
		else if (sign1 < -precision)
		{
			if (sign2 > precision)
			{
				return false; // aligned with e0, left of e1, right of e2
			}
			else
			{
				return true; // aligned with e0, left of e1, left of/aligned with e2
			}
		}
		else
		{
			if (sign2 > precision)
			{
				return true; // aligned with e0, aligned with e1, right of e2
			}
			else if (sign2 < -precision)
			{
				return true; // aligned with e0, aligned with e1, left of e2
			}
			else
			{
				// aligned with e0, aligned with e1, aligned with e2
				// t is a degenerate triangle, either sliver or point
				double dot0 = (t.v[1].x - p.x) * (t.v[0].x - p.x) + (t.v[1].y - p.y) * (t.v[0].y - p.y);
				if (dot0 <= precision)
				{
					return true; // belong to e0
				}
				else
				{
					double dot1 = (t.v[2].x - p.x) * (t.v[1].x - p.x) + (t.v[2].y - p.y) * (t.v[1].y - p.y);
					if (dot1 <= precision)
					{
						return true; // belong to e1
					}
                                        else
					{
						return false; // outside of e0 and e1
					}
				}
			}
		}
	}
};