QuadTreeIndex right_parent = GetNeighbour(nodes[start].parent, 1, 0);
if (right_parent == -1) return -1;
QuadTreeIndex right_parent = GetNeighbour(nodes[start].parent, 1, 0);
if (right_parent == -1) return -1;
QuadTreeIndex left_parent = GetNeighbour(nodes[start].parent, -1, 0);
if (left_parent == -1) return -1;
QuadTreeIndex left_parent = GetNeighbour(nodes[start].parent, -1, 0);
if (left_parent == -1) return -1;
QuadTreeIndex bottom_parent = GetNeighbour(nodes[start].parent, 0, 1);
if (bottom_parent == -1) return -1;
QuadTreeIndex bottom_parent = GetNeighbour(nodes[start].parent, 0, 1);
if (bottom_parent == -1) return -1;
QuadTreeIndex top_parent = GetNeighbour(nodes[start].parent, 0, -1);
if (top_parent == -1) return -1;
QuadTreeIndex top_parent = GetNeighbour(nodes[start].parent, 0, -1);
if (top_parent == -1) return -1;