Explanation and confirmation that DST filter is working

I am in the process of writing a free tutorial, for all of the image filters in KLWP, but I can not figure out how one would use the DST filter. I believe the filters in KLWP use Duff-Porter methods, but my understanding of how DST should work does not seem to be they way that it is implemented here. Could someone explain how they believe DST filter should work, and verify that it does work, and explain that here.

Thanks Mike

Sorry for the delay, Kustom applies the DST filter as explained here https://chiuki.github.io/android-shaders-filters/#/29 problem is that used in the way Kustom does it has no effect except just clearing the area, you should use a clipping mask to obtain the same effect, i will debug this better to understand why its not working.

Thank you for the reply.