"jr" <cre### [at] gmailcom> wrote:
> hi,
>
> "Bald Eagle" <cre### [at] netscapenet> wrote:
> > I also cannot find the following 2 functions in the code repository.
> > I can't search without being logged in, and username/pswd are scribbled down
> > somewhere at home.
> >
> >     MInvTransPoint(P, ray.Origin, Trans);
> >
> >     MInvTransDirection(D, ray.Direction, Trans);
> >
> > Anyone?
>
> core/math/matrix.h has the prototypes, hth.
>
> and thx re other thread.
>
>
> regards, jr.

Thanks, jr!

Ah, I think I (mostly) understand now.
matrix.h declares those inline functions for use in the namespace, and the
MInvTransPoint and MInvTransDirection functions just use the
MTransPoint and MTransDirection functions but somehow using the multiplicative
inverse of the transform matrix as input instead of the regular matrix.

in matrix.cpp, (line 535) we have

void Compute_Scaling_Transform (TRANSFORM *result, const Vector3d& vector)
{
    MIdentity (result->matrix);

    (result->matrix)[0][0] = vector[X];
    (result->matrix)[1][1] = vector[Y];
    (result->matrix)[2][2] = vector[Z];

    MIdentity (result->inverse);

    (result->inverse)[0][0] = 1.0 / vector[X];
    (result->inverse)[1][1] = 1.0 / vector[Y];
    (result->inverse)[2][2] = 1.0 / vector[Z];
}

and at line 155, there is:

void MIdentity (MATRIX result)
{
    int i, j;

    for (i = 0; i < 4; i++)
    {
        for (j = 0; j < 4; j++)
        {
            if (i == j)
            {
                result[i][j] = 1.0;
            }
            else
            {
                result[i][j] = 0.0;
            }
        }
    }
}

I'm still trying to get a feel for all of this, having only ever coded in "c++"
(Arduino) for maybe 6 months, several years back.

(Currently reading www.learncpp.com in small spurts, then I'll probably start
going through things with Stroustrup in hand to more rigorously work things
out.)

I guess perhaps in the same way that we can have operator overloading, where I
have two functions with the same name, but different input types,
a single function can yield one of several different types of outputs if that
class member access operator -> is used ...?

- BW

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