RFC: Smooth scrolling support in sun.awt.X11

[Philip Race]

I have no idea if you have contributed to OpenJDK before.,
If you have not, follow the instructions at 
https://openjdk.org/guide/#sign-the-oca
and in general read as much of that guide as makes sense for you.

After that I suggest a ROUGH draft github PR be posted here, so we can 
see what it
actually looks like in practice before you spend too much time on it.

-phil.

On 2/22/24 8:49 PM, Povilas Kanapickas wrote:
> Hi Philip,
>
> Thanks for a quick response. I will reply inline.
>
> On 2024-02-23 06:11, Philip Race wrote:
>> First, thank you for raising it this way rather than submitting a PR !
>>
>> In general things that compatibly and safely improve the user experience
>> are welcome.
>>
>> So at a high level, yes. So the next level is the details to think about
>> it more ?
>>
>> How important is smooth scrolling ? I've never noticed not having it.
>> Does it imply more ?
> Perhaps I should have used different terminology - pixel-perfect or
> high-resolution scrolling. The most visible artifact is that in a text
> view it's impossible to scroll by less than 3 line increments.
>
>> How much of this is useful without adding new API and therefore
>> applicable to 10 year old applications ?
>>
>> You speak of X11, but what about mac and windows ?
> Windows and Mac already has this.
>
> I believe that if application supports high-resolution scrolling on Mac
> or Windows then it should work on X11 without any changes. It will just
> get MouseWheelEvent in exactly the same way as on these platforms.
>
> However, application may have special code for e.g. emulating smooth
> scrolling on X11. In such case it will require changes to disable this
> code and just use Mac/Windows code path when native support is available.
>
>> And even for X11, we are (very slowly !) moving towards Wayland for the
>> future, so if this is just an X11-specific
>> implementation stop-gap, is it worth the effort ?
> I actually considered this exact question when deciding whether to
> pursue this. To me it seemed that awt on Wayland won't happen sooner
> than in 5 years. There's XWayland compatibility layer which means
> there's actually no real urgency to port applications to wayland because
> this doesn't offer any tangible benefit. And the amount of code in
> sun.awt.X11 is huge.
>
> Of course I could be completely wrong here as you know the openjdk
> priorities much better than I do :-)
>
>> If it is a contained, low risk, implementation only change, with no
>> changes to apps and benefits to users,
>> those are all good signs.
> I'm glad to hear that.
>
> Thanks a lot,
> Povilas
>
>> I invite others to chime in, especially anyone who knows something about
>> this X11 extension.
>>
>> -phil
>>
>>
>> On 2/22/24 6:23 PM, Povilas Kanapickas wrote:
>>> Hello,
>>>
>>> I would like to add smooth scrolling support to sun.awt.X11. At this
>>> point of time I already have this feature implemented. The code can be
>>> considered proof of concept right now, but it works and doesn't
>>> introduce regressions in all test scenarios I've done so far.
>>>
>>> Is this something that The Client Libraries Group would be interested in?
>>>
>>> The implementation consists of two parts.
>>>
>>> The first is adding support for X Input Extension 2.x protocol (XInput2)
>>> to sun.awt.X11. This protocol is quite different from the core X
>>> protocol that is currently used for input. Fortunately, it is possible
>>> to map XInput2 events back to core X input events almost exactly. Thus
>>> the addition for this new protocol involves relatively few code changes.
>>> Different functions need to be called here and there, but the bulk of
>>> code is reused as is by converting XInput2 events to core X input
>>> events. This reduces the risk of any regressions significantly.
>>>
>>> The second part is relatively simple wiring of XInput2 smooth scrolling
>>> events to MouseWheelEvent.
>>>
>>> This work would also lay ground for supporting gestures such as swipe or
>>> rotate on X11. This could be useful when these gestures are exposed in
>>> awt in the future. I implemented support for these gestures in the X
>>> server a couple of years ago and could potentially help exposing them in
>>> awt on macos and x11 too.
>>>
>>> Please let me know what you think about all this on a high level.
>>>
>>> Thank you,
>>> Povilas Kanapickas