RFC: Smooth scrolling support in sun.awt.X11

[Povilas Kanapickas]

On 2024-02-23 23:31, Philip Race wrote:
> 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.

Sounds good, thanks.

> 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.

The current code that I have is already in reviewable state.

I wanted to find all edge cases first, so that I don't waste reviewer's
time by changing the design later. Annoying a reviewer is a mortal error
when trying to contribute to an open source project. I better waste my
own time rewriting everything according to review comments :-)

Thanks,
Povilas

> 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
>