Bezier.java

Go to the documentation of this file.

package com.piro.bezier;
 
 
import eu.mihosoft.vrl.v3d.Vector3d;
 
public class Bezier
{
    float length;
    float[] coord;
 
    public Bezier(float sx, float sy, float[] coords, int numCoords)
    {
        setCoords(sx, sy, coords, numCoords);
    }
    
    public void setCoords(float sx, float sy, float[] coords, int numCoords)
    {
        coord = new float[numCoords * 2 + 2];
        coord[0] = sx;
        coord[1] = sy;
        for (int i = 0; i < numCoords; i++)
        {
            coord[i * 2 + 2] = coords[i * 2];
            coord[i * 2 + 3] = coords[i * 2 + 1];
        }
        
        calcLength();        
    }
    
    public float getLength()
    {
        return length;
    }
    
    private void calcLength()
    {
        length = 0;
        for (int i = 2; i < coord.length; i += 2)
        {
            length += lineLength(coord[i - 2], coord[i - 1], coord[i], coord[i + 1]);
        }
    }
    
    private float lineLength(float x1, float y1, float x2, float y2)
    {
        float dx = x2 - x1, dy = y2 - y1;
        return (float) Math.sqrt(dx * dx + dy * dy);
    }
    
    public Vector2 getFinalPoint(Vector2 point)
    {
        point.x = coord[coord.length - 2];
        point.y = coord[coord.length - 1];
        return point;
    }
    
     Vector3d eval(double param)
    {
        Vector2 point = new Vector2();
        point.x = 0;
        point.y = 0;
        int numKnots = coord.length / 2;
        
        for (int i = 0; i < numKnots; i++)
        {
            double scale = bernstein(numKnots - 1, i, param);
            point.x += coord[i * 2] * scale;
            point.y += coord[i * 2 + 1] * scale;
        }
        
        return new Vector3d(point.x,point.y);
    }
    
    private double bernstein(int numKnots, int knotNo, double param)
    {
        double iParam = 1 - param;
        //Faster evaluation for easy cases:
        switch (numKnots)
        {
            case 0:
                return 1;
            case 1:
            {
                switch (knotNo)
                {
                    case 0:
                        return iParam;
                    case 1:
                        return param;
                }
                break;
            }
            case 2:
            {
                switch (knotNo)
                {
                    case 0:
                        return iParam * iParam;
                    case 1:
                        return 2 * iParam * param;
                    case 2:
                        return param * param;
                }
                break;
            }
            case 3:
            {
                switch (knotNo)
                {
                    case 0:
                        return iParam * iParam * iParam;
                    case 1:
                        return 3 * iParam * iParam * param;
                    case 2:
                        return 3 * iParam * param * param;
                    case 3:
                        return param * param * param;
                }
                break;
            }
        }
        
        //If this bezier has more than four points, calculate bernstein the hard way
        double retVal = 1;
        for (int i = 0; i < knotNo; i++)
        {
            retVal *= param;
        }
        for (int i = 0; i < numKnots - knotNo; i++)
        {
            retVal *= iParam;
        }
        retVal *= choose(numKnots, knotNo);
        
        return retVal;
    }
    
    
    
    private int choose(int num, int denom)
    {
        int denom2 = num - denom;
        if (denom < denom2)
        {
            int tmp = denom;
            denom = denom2;
            denom2 = tmp;
        }
        
        int prod = 1;
        for (int i = num; i > denom; i--)
        {
            prod *= num;
        }
        
        for (int i = 2; i <= denom2; i++)
        {
            prod /= i;
        }
        
        return prod;
    }
}