How to grow that Quadtree at each node

Question

I have made a Quadtree which is initially a uniform level 2 quadtree.

struct qnode {
  int level;
  double xy[2];
  struct qnode *child[4];
};
typedef struct qnode Node;

int main( int argc, char **argv ) {

  Node *head;

  // make the head node
  head = makeNode( 0.0,0.0, 0 );

  // make a tree

  //full level 2 tree
  makeChildren( head );
  makeChildren( head->child[0] );
  makeChildren( head->child[1] );
  makeChildren( head->child[2] );
  makeChildren( head->child[3] );
}

// make a node at given location (x,y) and level

Node *makeNode( double x, double y, int level ) {

  int i;

  Node *node = (Node *)malloc(sizeof(Node));

  node->level = level;

  node->xy[0] = x;
  node->xy[1] = y;

  for( i=0;i<4;++i )
    node->child[i] = NULL;

  return node;
}

//split a leaf nodes into 4 children

void makeChildren( Node *parent ) {

  double x = parent->xy[0];
  double y = parent->xy[1];

  int level = parent->level;

  double hChild = pow(2.0,-(level+1));

  parent->child[0] = makeNode( x,y, level+1 );
  parent->child[1] = makeNode( x+hChild,y, level+1 );
  parent->child[2] = makeNode( x+hChild,y+hChild, level+1 );
  parent->child[3] = makeNode( x,y+hChild, level+1 );

  return;
}

How do I traverse each node and grow the tree uniformly at each node?

Answer 1

A recursive approach seems right. Something like this:

void growTree(Node * root) {
    for(int i=0; i<4; i++) {
        if(root->child[i] == NULL) root->child[i] = makeNode(0,0,root->level+1);
        else growTree(root->child[i]);
    }
}

I would also suggest redesigning makeNode. Something like this:

Node *makeNode(double x, double y, Node * node) {
    int level = node->level;
    // copy old body of makeNode here
}

Also, change to this:

typedef struct Node {
  int level;
  double xy[2];
  struct Node *child[4];
} Node;

There's no reason to have different names for struct Node and Node. If you want to hide the definition of struct Node, use this:

struct Node {
  int level;
  double xy[2];
  struct Node *child[4];
};

typedef struct Node Node;