/*
 * (C) 2004 - Geotechnical Software Services
 * 
 * This code is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public 
 * License as published by the Free Software Foundation; either 
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This code is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public 
 * License along with this program; if not, write to the Free 
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, 
 * MA  02111-1307, USA.
 */
package no.geosoft.cc.geometry.spline;




/**
 * A Bezier spline object. Use the SplineFactory class to create
 * splines of this type.
 * 
 * @author <a href="mailto:jacob.dreyer@geosoft.no">Jacob Dreyer</a>
 */   
class BezierSpline extends Spline
{
  /**
   * Construct a bezier spline. Package local; Use the SplineFactory
   * to create splines of this type. The control points are used according
   * to the definition of Bezier splines.
   * 
   * @param controlPoints  Control points of spline (x0,y0,z0,x1,y1,z1,...)
   * @param nParts         Number of parts in generated spline.
   */
  BezierSpline (double controlPoints[], int nParts)
  {
    controlPoints_ = controlPoints;
    nParts_ = nParts;
  }


  
  /**
   * Generate this spline.
   * 
   * @return  Coordinates of the spline (x0,y0,z0,x1,y1,z1,...)
   */
  double[] generate()
  {
    if (controlPoints_.length < 9) {
      double[] copy = new double[controlPoints_.length];
      System.arraycopy (controlPoints_, 0, copy, 0, controlPoints_.length);
      return copy;
    }
    
    int n = controlPoints_.length / 3;
    int length = (n - 3) * nParts_ + 1;
    double spline[] = new double[length * 3];

    p (0, 0, controlPoints_, spline, 0);
      
    int index = 3;
    for (int i = 0; i < n - 3; i += 3) {
      for (int j = 1; j <= nParts_; j++) {
        p (i, j / (double) nParts_, controlPoints_, spline, index);
        index += 3;
      }
    }
      
    return spline;      
  }

    
    
  private void p (int i, double t, double cp[], double spline[], int index)
  {
    double x = 0.0;
    double y = 0.0;
    double z = 0.0;
      
    int k = i;
    for (int j = 0; j <= 3; j++) {
      double b = blend (j, t);
      
      x += b * cp[k++];
      y += b * cp[k++];
      z += b * cp[k++];
    }
      
    spline[index + 0] = x;
    spline[index + 1] = y;
    spline[index + 2] = z;    
  }



  private double blend (int i, double t)
  {
    if      (i == 0) return (1 - t) * (1 - t) * (1 - t);
    else if (i == 1) return 3 * t * (1 - t) * (1 - t);
    else if (i == 2) return 3 * t * t * (1 - t);
    else             return t * t * t;
  }
}