/* Bezier spline with G1 continuity between control points */
import java.awt.*;

public class BezierG1 extends Bezier {

  /** Ensure G1 continuity by forcing control points to be collinear.
	If 0 1 2 3 4 5 6 are the the control points, then for the
	Beziers 0123 and 3456 to be G1 continuous at their join, 2, 3
	and 4 must be collinear */
  
  int deltax;
  int deltay;

  /* adjust positions of points so that points are collinear */
  void forceCollinear(int i) {
    if (i%3 == 0 && i<pts.npoints-1 && i>0) { //interpolating control point
      pts.xpoints[i-1] += deltax;  //adjust neighbours
      pts.ypoints[i-1] += deltay;  // by the same amount 
      pts.xpoints[i+1] += deltax;  // that this one has changed
      pts.ypoints[i+1] += deltay;
    } else if (i%3 == 1 && i > 1) {
      forceCollinear(i, i-1, i-2);
    } else if (i%3 == 2 && i < pts.npoints-2) {
      forceCollinear(i, i+1, i+2);
    }
  }

  /* move k such that it is collinear with i and j */
  void forceCollinear(int i, int j, int k) {
    float ij = distance(pts.xpoints[i],pts.ypoints[i],pts.xpoints[j],pts.ypoints[j]);
    float jk = distance(pts.xpoints[j],pts.ypoints[j],pts.xpoints[k],pts.ypoints[k]);
    float r = jk/ij;
    pts.xpoints[k] = Math.round(pts.xpoints[j]+r*(pts.xpoints[j]- pts.xpoints[i]));
    pts.ypoints[k] = Math.round(pts.ypoints[j]+r*(pts.ypoints[j]- pts.ypoints[i]));
  }

  float distance(int x1, int y1,int x2, int y2){
    return (float)Math.sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
  }

  /** add a control point, return index of new control point */
  public int addPoint(int x, int y) {
    int i = super.addPoint(x,y);
    forceCollinear(i);
    return i;
  }

  /** set selected control point */
  public void setPoint(int x, int y) {
    deltax = x-pts.xpoints[selection]; //save previous value
    deltay = y-pts.ypoints[selection]; //save previous value
    super.setPoint(x,y);
    forceCollinear(selection);
  }

  /** remove selected control point */
  public void removePoint() {
    super.removePoint();
    for (int i = 4; i < pts.npoints; i+=3) {
      forceCollinear(i);
    }
  }


}