Hello, everyone!

We use our custom frei0r plugin written in C++ , which does the same as corners filter, but ours use openCV. After we moved from Kdenlive 18.12.3 to 19.12.1 it broke a little.
Like corners filter ours had red lines and corners which were very useful to be moved by mouse. Now that red lines and corners disappeared. Params can still be changed by hand in Properties window, but it is not very convenient.
https://ibb.co/qsP5rPR

Maybe somebody has faced that problem or have an idea of what is wrong?
Thank you!

Stay with 18.12. OpenCV is not finally implemented so far.

Hum, not really: we still use OpenCV either directly (tracker filter) or through frei0r (even if few distributions build it completely, with contrib modules).
The thing is 19.04 was the release of a >2 years rewrite, and the UI has evolved a lot, especially the monitor that is now full QML.
I believe "traditional" corner filter has been ported, if yes you may check if we have a special xml effect description file to handle it.
Is your effect public? we could integrate it...