Cursor sizes on wayland

[Aleix Pol]

On Sun, May 13, 2018 at 5:34 PM, Martin Flöser <mgraesslin at kde.org> wrote:
> Am 2018-05-09 12:08, schrieb Aleix Pol:
>>
>> On Tue, May 8, 2018 at 8:57 PM, Martin Flöser <mgraesslin at kde.org> wrote:
>>>
>>>
>>>
>>> Am 8. Mai 2018 17:05:57 MESZ schrieb Aleix Pol <aleixpol at kde.org>:
>>>>
>>>> Hi,
>>>> I've been looking into getting a consistent cursor look on wayland,
>>>> which is specially daunting because of scaling.
>>>>
>>>> I'd like to look into fixing it for xwayland clients. Would somebody
>>>> be able to shed some light into the issue so I can understand it and
>>>> fix it?
>>>>
>>> Xwayland clients use the normal X11 API to set cursors. Xwayland just
>>> forwards them through the Wayland protocol. The env variable for cursor size
>>> is the same on Wayland and X11, so there should not be any difference.
>>>
>>> I'm not sure what exactly you want to look into. Personally I had the
>>> feeling that apps started to act crazy concerning cursor sizes - on Wayland
>>> and on X11. Normally there just should not be any difference. There's one
>>> env variable controlling it and if all apps would just use it and not do
>>> crazy stuff instead it would just work.
>>
>>
>> Well, setting the cursor size isn't any useful if you have two
>> monitors. I have it configured at resolution-dependent at the moment
>> and sometimes I lose my cursor on my high dpi screen.
>> If I use something bigger, when I move it to my external monitor I get
>> a monstrosity.
>>
>> David mentioned at the sprint that we maybe should be correcting its
>> scale on the kwin size, if it's not being scaled yet.
>
>
> This might be part of the solution. This needs a more general solution and
> might require changes to Wayland protocols and each toolkit and KWin.
>
> For "normal" windows we use the wl_surface::enter to inform on which output
> they are. Thus they can adjust for different dpi. Similar there is the scale
> information on a wl_surface.
>
> For a cursor wl_surface KWin neither emits the output information nor uses
> the scale information. Both would be relative easy to implement. But only
> makes sense if toolkits support it. Last time I looked at Qt code, Qt did
> not (but that's some time ago).
>
> So to get this properly working, I would suggest to add the output
> enter/leave information to cursor surfaces and honor scale in KWin. Then add
> the same to QtWayland if it doesn't exist already.
>
> Cheers
> Martin

The scale information should already be available in the surface, and
if it's not, then it should be added:
https://codereview.qt-project.org/#/c/227665/

Still we need to use this information.

Aleix