Marking synthesized scroll events as such.

Alexander Nyssen alexander at
Tue Aug 16 06:55:11 UTC 2016

Hi all,

as I am currently working on FXCanvas, there is one aspect I would like to discuss, which is closely related to JDK-8161282 <> (FXCanvas does not forward horizontal mouse scroll events to the embedded scene) and JDK-8143596 <> (FXCanvas does not forward touch gestures to embedded scene), namely handling of synthesized scroll events. That is, SWT synthesizes mouse wheel scroll events from PAN gesture events, and these are forwarded to the embedded scene (the patch I provided for JDK-8161282 does not change this behavior, it simply ensures horizontal and vertical mouse wheel events are processed equally) while not being marked as synthesized (unlike MouseEvent, ScrollEvent does not provide a ‚synthesized‘ flag). JavaFX natively seems to do likewise with SWIPE events, which seem to yield synthesized scroll events as well. 

Wouldn’t it be appropriate to introduce a synthesized flag and mark such kind of events as being synthesized? Within the Eclipse GEF’s FXCanvasEx we have sorted out scroll events synthesized form PAN events completely (and any client code may do likewise without accessing internal API, so this is no JIGSAW related issue), but I think it in general be nice if client code could properly decide, whether it wants to deal with these events or rather handle the native gesture events instead (as soon as JDK-8143596 is resolved this would even be possible in an SWT-integrated scenario).

I would raise an issue via webbug for this, if my thoughts are shared.


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