How to make infinite-scrolling GUI widgets under Wayland ?

[Jean-Michaël Celerier]

Thanks, it looks exactly like it. Now just have to see how to make it work
with Qt but that's another question :)

Kind regards,
Jean-Michaël

On Mon, Apr 26, 2021 at 5:08 PM Jonas Ådahl <jadahl at gmail.com> wrote:

> On Mon, Apr 26, 2021 at 04:57:01PM +0200, Jean-Michaël Celerier wrote:
> > Hello,
> > I am working on the multimedia sequencer ossia score (https://ossia.io).
> >
> > I am trying to make sure that it works fine for Linux users under
> wayland.
> >
> > For audio (and in general multimedia) apps, there is a very common family
> > of GUI widget which allows to scroll a value "infinitely" (or at least
> much
> > more than the height of the screen) - the usual user interaction is :
> > * User clicks on the widget : the mouse cursor disappears (some apps will
> > give a kind of highlight to the widget to indicate that it is being acted
> > upon)
> > * User moves their mouse upwards or downwards to increase the value
> > * At some point they reach the top or the bottom of the screen : to
> > continue scrolling transparently, the app translates the mouse cursor to
> > the top of the screen
> > * When the user releases the mouse the cursor reappears at the position
> > where it was clicked.
> >
> > This is needed in two case :
> > - To make sliders / knobs with easily adjustable values
> > - To implement infinite- or at least very long scrolling in minimaps.
> >
> > I made a few videos:
> > - Video 1: example of slider with the feature in Ableton Live (one of the
> > most used music making app) : https://streamable.com/ecepvc
> >
> > - Video 2 : example of minimap in Ableton Live :
> > https://streamable.com/epc7r1
> >
> > - Video 3 : Example of the pain induced by software that do not support
> the
> > feature: here I want to change the tempo but cannot because the mouse
> hits
> > the top of the screen. Thus I have to release and go click on it again :
> > https://streamable.com/bniht5
> >
> > Thus, my question is : what must I do as the developer of such an app to
> > make sure that my users will have widgets that will work "as expected"
> for
> > people in the media creation field, whatever the wayland compositor my
> > users are using (KDE Plasma, GNOME, sway...). I don't want them to have
> an
> > inferior user experience on Linux when compared to other operating
> systems.
> >
> > The googling I've done so far seems to say that there is no way to
> position
> > the cursor absolutely directly through wayland, but the only other way
> > seems to be through /dev/uinput which needs root permissions to write to
> > (and my userbase are artists who generally don't have the technical
> > skillset to know that they must mark things as root; I could always check
> > and show a popup that requests the user to do chmod u+rwx on /dev/uinput
> on
> > startup but that would be my last resort...)
>
> To implement the behavior shown in video 1 and 2, the "Wayland" way is
> depends on two protocols extension:
>
>  * Pointer locking extension[0]
>  * Relative pointer motions extension[1]
>
> With the core wl_pointer protocol object, you can control when the
> pointer cursor sprite is showing or not; with the pointer locking
> extension, you can effectively lock the pointer position to its
> position, meaning it will stay put and won't "escape" your application
> window; and lastly, with the relative pointer motions extension, you can
> receive pointer motions that are not affected by actual movement of the
> pointer cursor sprite, i.e. even if the pointer hit an edge or doesn't
> move, you'll still receive the motions as sent from the device.
>
> I think most compositors support these two protocol extensions as they
> are a corner stone in how e.g. 3D FPS games work.
>
>
> Jonas
>
> [0]
> https://gitlab.freedesktop.org/wayland/wayland-protocols/-/blob/master/unstable/pointer-constraints/pointer-constraints-unstable-v1.xml
> [1]
> https://gitlab.freedesktop.org/wayland/wayland-protocols/-/blob/master/unstable/relative-pointer/relative-pointer-unstable-v1.xml
>
> >
> > Thanks !
> > Jean-Michaël
>
> > _______________________________________________
> > wayland-devel mailing list
> > wayland-devel at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/wayland-devel
>
>
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