public void DrawPoint(Vector3 p, float size, Color color)
{
float h = size / 2; // half size
DrawLine(p + Vector3.UnitX * h, p - Vector3.UnitX * h, color);
DrawLine(p + Vector3.UnitY * h, p - Vector3.UnitY * h, color);
DrawLine(p + Vector3.UnitZ * h, p - Vector3.UnitZ * h, color);
}