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Help with Bezier curve algorithm, n amount of points?

807599Nov 16 2006 — edited Nov 23 2006
Hello,

I have tried to follow my graphics book but its way to complicated. The book uses openGL. I want to do it in java.

I need to use n amount of control points. I am going to use an applet, and basically hard code the control points in the program. Nothing fancy.



I tried to change this c code to java format, but I cant get it to work at all.
Does any one have an algorithm already written, or help me improve this one.

thanks.
/*
Code to generate a cubic Bezier curve
*/

typedef struct
{
    float x;
    float y;
}
Point2D;

/*
cp is a 4 element array where:
cp[0] is the starting point, or P0 in the above diagram
cp[1] is the first control point, or P1 in the above diagram
cp[2] is the second control point, or P2 in the above diagram
cp[3] is the end point, or P3 in the above diagram
t is the parameter value, 0 <= t <= 1
*/

Point2D PointOnCubicBezier( Point2D* cp, float t )
{
    float   ax, bx, cx;
    float   ay, by, cy;
    float   tSquared, tCubed;
    Point2D result;

    /* calculate the polynomial coefficients */

    cx = 3.0 * (cp[1].x - cp[0].x);
    bx = 3.0 * (cp[2].x - cp[1].x) - cx;
    ax = cp[3].x - cp[0].x - cx - bx;
        
    cy = 3.0 * (cp[1].y - cp[0].y);
    by = 3.0 * (cp[2].y - cp[1].y) - cy;
    ay = cp[3].y - cp[0].y - cy - by;
        
    /* calculate the curve point at parameter value t */
        
    tSquared = t * t;
    tCubed = tSquared * t;
        
    result.x = (ax * tCubed) + (bx * tSquared) + (cx * t) + cp[0].x;
    result.y = (ay * tCubed) + (by * tSquared) + (cy * t) + cp[0].y;
        
    return result;
}

/*
 ComputeBezier fills an array of Point2D structs with the curve   
 points generated from the control points cp. Caller must 
 allocate sufficient memory for the result, which is 
 <sizeof(Point2D) numberOfPoints>
*/

void ComputeBezier( Point2D* cp, int numberOfPoints, Point2D* curve ) {
    float   dt;
    int   i;

    dt = 1.0 / ( numberOfPoints - 1 );

    for( i = 0; i < numberOfPoints; i++)
        curve[i] = PointOnCubicBezier( cp, i*dt );
}

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Locked on Dec 21 2006
Added on Nov 16 2006
16 comments
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