/*  BezierCurve.java
 *
 *  Draw a Bezier curve using the parametric form.
 *
 *  Bruce M. Bolden
 *  April 30, 2001
 *  http://www.cs.uidaho.edu/~bruceb/cs127/code/Bezier/
 */

import java.awt.*;

public class BezierCurve
{
    static final int INSET = 80;
    static final int MIN_DIVISIONS = 10;
    static final int POINT_SIZE = 3;

    Point b[] = new Point[4];       //  Vertices of the control polygon
    int nDivs = 25;                 //  divisions of the Bezier curve

    int windowSize;                 //  display region size
    Color background;

    BezierCurve( Color bgC, int h, int w )
    {
        background = bgC;
        windowSize = Math.min( h, w );  // minimum of height and width

        b[0] = new Point( INSET, windowSize-INSET );
        b[1] = new Point( INSET, INSET );
        b[2] = new Point( windowSize-INSET, INSET );
        b[3] = new Point( windowSize-INSET, windowSize-INSET );
    }

    void setDivisions( int n )
    {
            // Negative or less than 10 is useless
        nDivs = Math.max( n, MIN_DIVISIONS );
    }

    /** Draw Bezier curve using "nDivs" divisions.
     */
    public void drawBezierCurve( Graphics g )
    {
        g.setColor( background );
        g.fillRect( 0, 0, windowSize, windowSize );

           //  Check points/Show control polygon
        g.setColor( Color.yellow );
        g.drawLine( b[0].x, b[0].y, b[1].x, b[1].y );
        g.drawLine( b[1].x, b[1].y, b[2].x, b[2].y );
        g.drawLine( b[2].x, b[2].y, b[3].x, b[3].y );
        g.setColor(Color.gray);
        g.drawLine( b[3].x, b[3].y, b[0].x, b[0].y );

        for( int i = 0 ; i < b.length ; i++ )
        {
            g.fillOval( b[i].x, b[i].y, 2*POINT_SIZE, 2*POINT_SIZE );
            
            //System.out.print( "b[" + i + "]: " );
            //System.out.println( b[i].x + ", " + b[i].y );
        }

            //  Display points on curve
        g.setColor(Color.red);         //  point color
        Point p = new Point();

        double t;                      //  parametric value
        double onemt;                  //  (1-t)
        double onemt2;                 //  (1-t)^2
        double j30, j31, j32, j33;     //  Bernstein coefficients

        for( t = 0.0 ; t <= 1.0 ; t += 1.0/(double)nDivs )
        {
            onemt = 1.0 - t;
            onemt2 = onemt * onemt;
            j30 = onemt * onemt2;      //  (1-t)^3
            j31 = 3.0*t * onemt2;
            j32 = 3.0*t*t * onemt;
            j33 = t * t * t;

            p.x = (int)(j30*b[0].x + j31*b[1].x + j32*b[2].x + j33*b[3].x);
            p.y = (int)(j30*b[0].y + j31*b[1].y + j32*b[2].y + j33*b[3].y);

            //System.out.println( "p[" + t + "]: " + p.x + ", " + p.y );

            g.fillOval( p.x, p.y, POINT_SIZE, POINT_SIZE );
        }
    }
}