closest_point_on_segment()

void closest_point_on_segment	(	const POINT4D *	p,
		const POINT4D *	A,
		const POINT4D *	B,
		POINT4D *	ret
	)

Definition at line 1258 of file ptarray.c.

References FP_EQUALS, POINT4D::m, r, POINT4D::x, POINT4D::y, and POINT4D::z.

Referenced by lwline_split_by_point_to(), and ptarray_locate_point().

{
        double r;

        if (  FP_EQUALS(A->x, B->x) && FP_EQUALS(A->y, B->y) )
        {
                *ret = *A;
                return;
        }

        /*
         * We use comp.graphics.algorithms Frequently Asked Questions method
         *
         * (1)           AC dot AB
         *           r = ----------
         *                ||AB||^2
         *      r has the following meaning:
         *      r=0 P = A
         *      r=1 P = B
         *      r<0 P is on the backward extension of AB
         *      r>1 P is on the forward extension of AB
         *      0<r<1 P is interior to AB
         *
         */
        r = ( (p->x-A->x) * (B->x-A->x) + (p->y-A->y) * (B->y-A->y) )/( (B->x-A->x)*(B->x-A->x) +(B->y-A->y)*(B->y-A->y) );

        if (r<0)
        {
                *ret = *A;
                return;
        }
        if (r>1)
        {
                *ret = *B;
                return;
        }

        ret->x = A->x + ( (B->x - A->x) * r );
        ret->y = A->y + ( (B->y - A->y) * r );
        ret->z = A->z + ( (B->z - A->z) * r );
        ret->m = A->m + ( (B->m - A->m) * r );
}

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