A vector orthogonal projection to B

1. Even a vector dot multiply

Two vector points by
static double Dot (const double A[3],const Double b[3]) {return
    (A[0]*b[0] + a[1]*b[1] + a[2]*b[2);
}

2. Two vector x multiplication

Vector x by
void Crossvector (const double A[3],const double b[3],double normal[3]) {
    normal[0] = a[1] * b[2]-a[2] * b[ 1];
    NORMAL[1] = a[2] * b[0]-a[0] * b[2];
    NORMAL[2] = a[0] * b[1]-a[1] * b[0];

3. Multiply a value by a vector

Product
static void Multiplyvector (double a[3],double scalar) for a vector {for
    (unsigned int i=0; i<3; i++) {
        a[ I] *= scalar;
    }

4.a vector orthogonal projection to B

A vector orthogonal projection to B
-bool Vectorprojection (const double A[3],const double b[3],double a1[3]) {
    double bsq = Dot (b,b);
    Determine whether B is 0
    if (0 = bsq) {
        a1[0] = 0;
        A1[1] = 0;
        A1[2] = 0;
        return false;
    }

    float ratio = Dot (a,b)/bsq;
    for (unsigned int i=0; i<3; i++) {
        a1[i] = B[i];
    }
    Multiplyvector (a1,ratio);
    return true;
}

A detailed interpretation of https://www.cnblogs.com/graphics/archive/2010/08/03/1791626.html by vector projection