Exemplo n.º 1
0
/*
 *  GenerateBezier :
 *  Use least-squares method to find Bezier control points for region.
 *
 */
static BezierCurve  GenerateBezier(Point2 *d, int first, int last, double *uPrime,
        Vector2 tHat1, Vector2 tHat2)
{
    int     i;
    Vector2     A[MAXPOINTS][2];    /* Precomputed rhs for eqn  */
    int     nPts;           /* Number of pts in sub-curve */
    double  C[2][2];            /* Matrix C     */
    double  X[2];           /* Matrix X         */
    double  det_C0_C1,      /* Determinants of matrices */
            det_C0_X,
            det_X_C1;
    double  alpha_l,        /* Alpha values, left and right */
            alpha_r;
    Vector2     tmp;            /* Utility variable     */
    BezierCurve bezCurve;   /* RETURN bezier curve ctl pts  */

    bezCurve = (Point2 *)malloc(4 * sizeof(Point2));
    nPts = last - first + 1;


    /* Compute the A's  */
    for (i = 0; i < nPts; i++) {
        Vector2     v1, v2;
        v1 = tHat1;
        v2 = tHat2;
        V2Scale(&v1, B1(uPrime[i]));
        V2Scale(&v2, B2(uPrime[i]));
        A[i][0] = v1;
        A[i][1] = v2;
    }

    /* Create the C and X matrices  */
    C[0][0] = 0.0;
    C[0][1] = 0.0;
    C[1][0] = 0.0;
    C[1][1] = 0.0;
    X[0]    = 0.0;
    X[1]    = 0.0;

    for (i = 0; i < nPts; i++) {
        C[0][0] += V2Dot(&A[i][0], &A[i][0]);
        C[0][1] += V2Dot(&A[i][0], &A[i][1]);
/*                  C[1][0] += V2Dot(&A[i][0], &A[i][1]);*/
        C[1][0] = C[0][1];
        C[1][1] += V2Dot(&A[i][1], &A[i][1]);

        tmp = V2SubII(d[first + i],
            V2AddII(
              V2ScaleIII(d[first], B0(uPrime[i])),
                V2AddII(
                    V2ScaleIII(d[first], B1(uPrime[i])),
                            V2AddII(
                            V2ScaleIII(d[last], B2(uPrime[i])),
                                V2ScaleIII(d[last], B3(uPrime[i]))))));


        X[0] += V2Dot(&A[i][0], &tmp);
        X[1] += V2Dot(&A[i][1], &tmp);
    }

    /* Compute the determinants of C and X  */
    det_C0_C1 = C[0][0] * C[1][1] - C[1][0] * C[0][1];
    det_C0_X  = C[0][0] * X[1]    - C[1][0] * X[0];
    det_X_C1  = X[0]    * C[1][1] - X[1]    * C[0][1];

    /* Finally, derive alpha values */
    alpha_l = (det_C0_C1 < ZERO_TOLERANCE) ? 0.0 : det_X_C1 / det_C0_C1;
    alpha_r = (det_C0_C1 < ZERO_TOLERANCE) ? 0.0 : det_C0_X / det_C0_C1;

    /* If alpha negative, use the Wu/Barsky heuristic (see text) */
    /* (if alpha is 0, you get coincident control points that lead to
     * divide by zero in any subsequent NewtonRaphsonRootFind() call. */
    double segLength = V2DistanceBetween2Points(&d[last], &d[first]);
    double epsilon = 1.0e-6 * segLength;
    if (alpha_l < epsilon || alpha_r < epsilon)
    {
        /* fall back on standard (probably inaccurate) formula, and subdivide further if needed. */
        double dist = segLength / 3.0;
        bezCurve[0] = d[first];
        bezCurve[3] = d[last];
        V2Add(&bezCurve[0], V2Scale(&tHat1, dist), &bezCurve[1]);
        V2Add(&bezCurve[3], V2Scale(&tHat2, dist), &bezCurve[2]);
        return (bezCurve);
    }

    /*  First and last control points of the Bezier curve are */
    /*  positioned exactly at the first and last data points */
    /*  Control points 1 and 2 are positioned an alpha distance out */
    /*  on the tangent vectors, left and right, respectively */
    bezCurve[0] = d[first];
    bezCurve[3] = d[last];
    V2Add(&bezCurve[0], V2Scale(&tHat1, alpha_l), &bezCurve[1]);
    V2Add(&bezCurve[3], V2Scale(&tHat2, alpha_r), &bezCurve[2]);
    return (bezCurve);
}
Exemplo n.º 2
0
/*
 *  GenerateBezier :
 *  Use least-squares method to find Bezier control points for region.
 *
 */
static BezierCurve  GenerateBezier(
    Point2	*d,			/*  Array of digitized points	*/
    int		first, int last,		/*  Indices defining region	*/
    double	*uPrime,		/*  Parameter values for region */
    Vector2	tHat1, Vector2 tHat2)	/*  Unit tangents at endpoints	*/
{
    int 	i;
//    Vector2 	A[MAXPOINTS][2];	/* Precomputed rhs for eqn	*/
    int 	nPts;			/* Number of pts in sub-curve */
    double 	C[2][2];			/* Matrix C		*/
    double 	X[2];			/* Matrix X			*/
    double 	det_C0_C1,		/* Determinants of matrices	*/
    	   	det_C0_X,
	   		det_X_C1;
    double 	alpha_l,		/* Alpha values, left and right	*/
    	   	alpha_r;
    Vector2 	tmp;			/* Utility variable		*/
    BezierCurve	bezCurve;	/* RETURN bezier curve ctl pts	*/

    bezCurve = (Point2 *)malloc(4 * sizeof(Point2));
    nPts = last - first + 1;

    Vector2 (*A)[2];
	 
	 A = new Vector2[nPts][2];	/* Precomputed rhs for eqn	*/
 
    /* Compute the A's	*/
    for (i = 0; i < nPts; i++) {
		Vector2		v1, v2;
		v1 = tHat1;
		v2 = tHat2;
		V2Scale(&v1, B1(uPrime[i]));
		V2Scale(&v2, B2(uPrime[i]));
		A[i][0] = v1;
		A[i][1] = v2;
    }

    /* Create the C and X matrices	*/
    C[0][0] = 0.0;
    C[0][1] = 0.0;
    C[1][0] = 0.0;
    C[1][1] = 0.0;
    X[0]    = 0.0;
    X[1]    = 0.0;

    for (i = 0; i < nPts; i++) {
        C[0][0] += V2Dot(&A[i][0], &A[i][0]);
		C[0][1] += V2Dot(&A[i][0], &A[i][1]);
/*					C[1][0] += V2Dot(&A[i][0], &A[i][1]);*/	
		C[1][0] = C[0][1];
		C[1][1] += V2Dot(&A[i][1], &A[i][1]);

		tmp = V2SubII(d[first + i],
	        V2AddII(
	          V2ScaleIII(d[first], B0(uPrime[i])),
		    	V2AddII(
		      		V2ScaleIII(d[first], B1(uPrime[i])),
		        			V2AddII(
	                  		V2ScaleIII(d[last], B2(uPrime[i])),
	                    		V2ScaleIII(d[last], B3(uPrime[i]))))));
	

	X[0] += V2Dot(&A[i][0], &tmp);
	X[1] += V2Dot(&A[i][1], &tmp);
    }

    /* Compute the determinants of C and X	*/
    det_C0_C1 = C[0][0] * C[1][1] - C[1][0] * C[0][1];
    det_C0_X  = C[0][0] * X[1]    - C[0][1] * X[0];
    det_X_C1  = X[0]    * C[1][1] - X[1]    * C[0][1];

    /* Finally, derive alpha values	*/
    if (det_C0_C1 == 0.0) {
		det_C0_C1 = (C[0][0] * C[1][1]) * 10e-12;
    }
    alpha_l = det_X_C1 / det_C0_C1;
    alpha_r = det_C0_X / det_C0_C1;


    /*  If alpha negative, use the Wu/Barsky heuristic (see text) */
    if (alpha_l < 0.0 || alpha_r < 0.0) {
		double	dist = V2DistanceBetween2Points(&d[last], &d[first]) /
					3.0;

		bezCurve[0] = d[first];
		bezCurve[3] = d[last];
		V2Add(&bezCurve[0], V2Scale(&tHat1, dist), &bezCurve[1]);
		V2Add(&bezCurve[3], V2Scale(&tHat2, dist), &bezCurve[2]);

		delete[] A;

		return (bezCurve);
    }

    /*  First and last control points of the Bezier curve are */
    /*  positioned exactly at the first and last data points */
    /*  Control points 1 and 2 are positioned an alpha distance out */
    /*  on the tangent vectors, left and right, respectively */
    bezCurve[0] = d[first];
    bezCurve[3] = d[last];
    V2Add(&bezCurve[0], V2Scale(&tHat1, alpha_l), &bezCurve[1]);
    V2Add(&bezCurve[3], V2Scale(&tHat2, alpha_r), &bezCurve[2]);

	 delete[] A;

    return (bezCurve);
}