typedef struct Quad Quad;typedef struct QuadTree QuadTree; #pragma incomplete QuadTree enum{	QNCIRCLE,	QNRECTANGLE,}; struct Quad{	int type;	union {		/* circle */		struct {			Point p;			int radius;		};		/* rectangle */		struct {			Rectangle r;		};	};	void *aux;}; /* XXX: should be hidden in quad.c */enum{	QTNW = 0,	QTNE,	QTSW,	QTSE,	QTNZONE,}; typedef struct QuadTree QuadTree;struct QuadTree{	Rectangle boundary; 	Quad *quads;	int nquads;	int maxquads; 	/* QTNZONE QuadTrees */	QuadTree *zones;}; Quad qcircle(Point p, int radius, void *aux);Quad qrect(Rectangle r, void *aux);Rectangle quad2rect(Quad v); QuadTree *qtmk(Rectangle aabb);int qtinsert(QuadTree *qt, Quad v);void qtsubdivide(QuadTree *qt);Point *qtquery(QuadTree *qt, Rectangle aabb, int *npoint);void qtclear(QuadTree *qt);int qtsearch(QuadTree *qt, Rectangle r, Quad **res, int *nres);