cImageResizer / cCairoMatrix: Adding "width/height-only" controlpoints

Hello!

I would like to add controlpoints to the cImageResize class that can be found in the Cairo Tutorial (https://github.com/vbRichClient/CairoTutorial).
These should be used along with the other controlpoints (meaning I would like to keep the controlpoints to scale width and height together / dependently).

The control points should be usable to change just the width or just the height.

I have tried it, but I don't manage the matrix stuff, and my attempts are getting wilder and wilder, but I don't succeed.

Can somebody help me in this case?

It would be much appreciated.
Thank you!