import java.awt.*;

public class ScanLine extends poly {
  
    IEL iel;
    AEL ael;
    int y;
    int i;
    int xstart, xend;  

    public String showState() {
	/* highlight active edges */

	return "y = " + y + "  i = " + i + "  start " + xstart + "  end " + xend +
	    "\nActive Edge List =\n" + ael +
	    "\nInactive Edge List =\n" + iel;
    }


    void drawPolygon(Polygon p){
	iel = new IEL();
	ael = new AEL();
	if (p.npoints <= 2) return;
	/* build IEL */
	for (int i = 1; i < p.npoints; i++) {
	    Edge e = new Edge(p.xpoints[i-1],p.ypoints[i-1],p.xpoints[i],p.ypoints[i]);
	    iel.add(e);
	}
	iel.add(new Edge(p.xpoints[p.npoints-1],p.ypoints[p.npoints-1],p.xpoints[0],p.ypoints[0]));
    
	/* loop over each scan line */
	for (y = iel.miny(); y <= iel.maxy(); y++){
	    Edge e;
	    while ((e=iel.next(y))!=null) {
		ael.add(e,y);
	    }
	    ael.deleteEdges(y);
	    for (i = 0; i < ael.size(); i += 2) {
                xstart = ael.elementAt(i).xofi(y);
		xend = ael.elementAt(i+1).xofi(y);
		fillSpan(xstart, xend, y);
		if (step()) return;
	    }
	}
	if (step()) return;
    }
  
  
}