General  Fix point Scaling 

In computer graphics, scaling refers to the transformation of an object in such a way that its size changes. In general, scaling can be performed around any point in space, and not just the origin. When we scale an object around a fixed point, we call it fixed-point scaling.

To perform a fixed-point scaling, we need to perform the following steps:

1. Translate the object so that the fixed point is at the origin.

```

T1 = [ 1  0  0  -px ]

     [ 0  1  0  -py ]

     [ 0  0  1  -pz ]

     [ 0  0  0   1  ]

```

2. Scale the object with respect to the origin.

```

S = [ sx  0   0   0 ]

    [ 0   sy  0   0 ]

    [ 0   0   sz  0 ]

    [ 0   0   0   1 ]

```

3. Translate the object back to its original position.

```

T2 = [ 1  0  0  px ]

     [ 0  1  0  py ]

     [ 0  0  1  pz ]

     [ 0  0  0  1  ]

```

4. Combine the above transformations to form a composite transformation matrix `M`.

```

M = T2 * S * T1

```

Here, `(px, py, pz)` is the fixed point around which we want to scale, and `(sx, sy, sz)` are the scaling factors in the x, y, and z directions respectively.

Note that the order of the transformations is important. We first translate the object so that the fixed point is at the origin, then scale it around the origin, and finally translate it back to its original position. If we change the order of the transformations, we may get a different result.

Also, note that the above method assumes that the fixed point is not translated during the scaling operation. If the fixed point is also supposed to move along with the object during scaling, we need to modify the translation component of the transformation accordingly.