[RFC weston] clients: Don't attach a buffer if mouse cursor surface is unchanged

[Daniel Stone]

Hey Derek,

On Thu, 22 Feb 2018 at 22:16, Derek Foreman <derekf at osg.samsung.com> wrote:
> Keep track of what cusor image buffer is attached to the cursor
> surface and avoid re-attaching it if we don't have to.
>
> This isn't just an obviously pointless optimization, it turns all
> of toy toolkit into a test case for handling this properly.
>
> Signed-off-by: Derek Foreman <derekf at osg.samsung.com>
> ---
>
> Continuing my streak of posting unpopular patches, this patch breaks
> weston, so I'm not pushing for inclusion, but I think we need to
> resolve why it breaks, and fix either weston or wayland documentation
> to reflect expected behaviour.
>
> I think this can be attributed to a weston bug, and we should be able to
> expect that the compositor will be able to redisplay the surface without
> needing to attach a new buffer, and that if the compositor has released
> the buffer then it has a kept copy somewhere...
>
> Any other opinions?

Hmm, I'm really not sure what to think about this.

I take it the problem is that the client sets a particular surface as
the pointer surface, loses focus, sets the same surface as the pointer
surface on re-enter after not changing the content, and then the
content is never shown?

If so, the two solutions would be:
  - the surface content should be preserved across leave/enter; Weston
is buggy for not showing the content on re-enter
  - mouse leave and your surface no longer being shown as a pointer
surface causes the surface to lose that role; Wayland protocol spec
should explicitly state this

I have a very slight lean towards the latter because it more closely
matches my recollection of what the XDG roles do. But that
recollection might be totally wrong, who knows.

Cheers,
Daniel