[PATCH] documentation: clarify the need for wl_surface.damage

[Mahdi Khanalizadeh]

Hi,
thanks for reviewing.

Am 03.10.2017 09:02:03 schrieb(en) Pekka Paalanen:
> On Mon,  2 Oct 2017 17:39:56 +0200
> Mahdi Khanalizadeh <mahdi at khanalizadeh.com> wrote:
> 
> > Add an explanation for wl_surface.attach why a wl_surface.damage  
> request
> > is necessary. Explicitly declare it implementation defined  
> behaviour if the
> > wl_surface.damage request is omitted to give the compositor some  
> leeway
> > on how it handles attaches.
> >
> > Signed-off-by: Mahdi Khanalizadeh <mahdi at khanalizadeh.com>
> > ---
> >  protocol/wayland.xml | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/protocol/wayland.xml b/protocol/wayland.xml
> > index aabc7ae..6f6cc11 100644
> > --- a/protocol/wayland.xml
> > +++ b/protocol/wayland.xml
> > @@ -1365,6 +1365,11 @@
> >  	wl_buffer before receiving the wl_buffer.release event, the  
> surface
> >  	contents become undefined immediately.
> >
> > +	Attaching a buffer should always be accompanied by a
> > +	wl_surface.damage request to signal the compositor that the
> > +	contents of the buffer have changed. Otherwise it is  
> implementation
> > +	defined whether the wl_surface.attach request has any visible  
> effect.
> 
> Hi,
> 
> thank you for the clarification, I assume this is as a response to our
> IRC discussion.
Indeed.

> How about phrasing it: "Attaching a buffer should always be  
> accompanied
> by at least one wl_surface.damage request to signal the compositor
> which parts of the surface contents are changed."?
> 
> - There can be multiple damage requests to build up a complex region.
> - It's not about buffer contents, it is about surface contents.
> - We don't want to imply that you must always give full surface-sized
>   damage when the buffer is swapped.
> 
> However, most of the new paragraph are redundant with the first
> paragraph for the damage request. Could you instead add one more
> sentence to the first paragraph explaining that the compositor has no
> obligation to use the new contents outside of the given damage?
> 
> There is also the request damage_buffer which is otherwise the same  
> but
> uses a different coordinate system.
Taking your suggestions into account, what’s your opinion on adding the  
following
sentence after the first paragraphs of damage and damage_buffer instead  
of
my original change?

“For this reason every wl_surface.attach request should always be
accompanied by at least one wl_surface.damage or
wl_surface.damage_buffer request to signal the compositor which
parts of the surface contents have changed, because the compositor
is not obliged to update any surface content that falls outside of the
damaged area.”

> > +
> >  	If wl_surface.attach is sent with a NULL wl_buffer, the
> >  	following wl_surface.commit will remove the surface content.
> >        </description>
> 
> Thanks,
> pq
> 
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