[PATCH] [weston, v4] weston.ini: Add natural scroll support to weston.ini This adds support for enabling/disabling natural scrolling via a boolean in weston.ini:

[Peter Hutterer]

On Mon, Feb 06, 2017 at 12:00:08PM +0200, Pekka Paalanen wrote:
> On Mon, 6 Feb 2017 10:36:56 +1000
> Peter Hutterer <peter.hutterer at who-t.net> wrote:
> 
> > On Sun, Feb 05, 2017 at 07:30:18PM -0500, Jiayi Zhao wrote:
> > > ​​
> > > Hmmm, after using udev_device_has_tag(udev_device, "ID_INPUT_TOUCHPAD"),
> > > I'm getting linking errors. Quick google of this leads to: libraries on the
> > > command line should be after the object files being compiled.
> > > Is this a bug?  
> > 
> > come to think of it, tags are a bit different. you need
> > udev_device_get_property_value() instead. and you need to make sure that
> > libudev is linked in - that's where your linking errors come from.
> 
> Hi,
> 
> needing udev API raises further considerations.
> 
> A fundamental question is whether udev-using backends should actually
> expose udev as part of their API to libweston users (main.c) or whether
> it should expose its own abstraction. Since we (I, at least) do not
> really have a good understanding what all things one might want, it
> might be easier and more flexible to assume that udev will be part of
> libweston's DRM backend specific API.
> 
> IOW, in compositor-drm.h, the configure_device vfunc should probably
> get a new argument referring to the udev thing. This breaks the library
> ABI, forcing a libweston major version bump.
> 
> Therefore when the DRM-backend is enabled, weston (main.c) should link
> to libudev for using it, and the backend-specific API needs to grow
> things to support the use of udev. This calls for configure.ac changes.
> 
> So far Weston has not been using libudev, which is why you got the
> linker errors: it is not linked into Weston, it is only linked to the
> specific backends.
> 
> Also, it has been possible to build Weston and libweston without
> libudev by disabling the backends that depended on it. I'm not sure
> supporting that is worthwhile, though, considering DRM is really the
> main backend which already depends on libudev.

afaict libinput isn't optional and libinput requires libudev. So now we're
only talking about whether you explicitly link to it or not, it's already a
requirement anyway.

two points regarding the API discussion, and both sum up as "not needed for
this particular feature".

if udev were unavailable, it'd be easier to have a policy of "if the device
has tapping, treat it as touchpad for the natural scroll setting". that's
good enough and skirts any usage of libudev in main.c.

but we already have a libinput device here and libinput links to libudev. We
easily get the udev device from the libinput device, the only change here  
is linking libudev explicitly. no API changes to libweston needed at all.

changing the API for a little feature like this seems excessive unless you
have explicit use-cases where exposing udev through the API is required. 

Cheers,
   Peter


> Looks like libinput is already required by main.c, so following that
> example with libudev should be good.

> 
> Thanks,
> pq
> 
> > > On Sun, Feb 5, 2017 at 7:20 PM, Peter Hutterer <peter.hutterer at who-t.net>
> > > wrote:
> > >   
> > > > On Sun, Feb 05, 2017 at 07:13:04PM -0500, Jiayi Zhao wrote:  
> > > > > How would ID_INPUT_TOUCHPAD work?
> > > > > I have something like udev_device_has_tag(udev_device,  
> > > > ID_INPUT_TOUCHPAD)  
> > > > > Unfortunately, I'm not sure where this constant is declared and its  
> > > > unable  
> > > > > to find the tag. :/  
> > > >
> > > > it's a udev property name, so use it as a string, not a #define.
> > > > value is either 1 or 0, so you do need to check for validity.
> > > >
> > > > Cheers,
> > > >    Peter
> > > >  
> > > > > On Jan 29, 2017 4:42 PM, "Peter Hutterer" <peter.hutterer at who-t.net>  
> > > > wrote:  
> > > > >  
> > > > > > On Fri, Jan 27, 2017 at 09:46:49PM -0500, Jiayi Zhao wrote:  
> > > > > > > [libinput]
> > > > > > > natural_scroll=true
> > > > > > >
> > > > > > > CHANGES:
> > > > > > >  - libinput_device_config_scroll_has_natural_scroll() is no longer  
> > > > > > compared to != 0  
> > > > > > >  - added configuration option to weston.ini man page
> > > > > > >
> > > > > > > Signed-off-by: Jiayi Zhao <jeff.no.zhao at gmail.com>
> > > > > > > ---
> > > > > > >  compositor/main.c  | 13 +++++++++++++
> > > > > > >  man/weston.ini.man |  3 +++
> > > > > > >  weston.ini.in      |  1 +
> > > > > > >  3 files changed, 17 insertions(+)
>