I have found that the image had good support for MouseWheelEvents for a while. Based on the method stamps it seems Marcel added the necessary image-side code on 6/10/2016 via the `MouseWheelEvent` and `MouseWheelState` classes.
The original comment that you pointed out in the opensmalltalk sources comes from commit 3010e4465405f6ec7a289fc3a3d21eb324816a8f
You're right though that images from before October '16 on X11 would find themselves without scroll support. Do the images have some sort of capability advertising system or will this need to be a primitive invoked on system startup?
I believe this is a rather urgent fix. As Chris already pointed out on the mailing list, it effectively makes scrolling in any function larger than the code panel effectively impossible on X11 in 5.2. Or at least I keep slipping in horizontal scroll events when using my touchpad. If this PR turns out to be a major undertaking, however, we may be better off reverting the commit that enabled horizontal scroll events in the first place for the moment and revisit this afterwards with the cleanest possible solution.
What is the scope of backwards compatibility for the VM? Are breaking changes like this allowed in major version increments (e.g. 5.2->5.3 or 5.2->6.0) or to be avoided at all cost?