[PATCH weston 2/2] compositor: surface and view output comment fixes

[Jonas Ådahl]

On Mon, May 16, 2016 at 04:45:05PM +0200, Armin Krezović wrote:
> On 10.05.2016 16:10, Pekka Paalanen wrote:
> > From: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
> > 
> > weston_surface::output and weston_view::output as used for different
> > purposes. Only the surface output is used for frame callbacks.
> > 
> > The uses of the view output are much more vague and hard to describe.
> > 
> > Also fix a comment mistake in weston_surface_assign_output().
> > 
> 
> All the changes look fine to me. I have one comment below, as I'm not sure
> if it's a mistake or not.
> 
> In case it isn't a mistake (or with the mistake fixed, in case it is one),
> this patch is also:
> 
> Reviewed-by: Armin Krezović <krezovic.armin at gmail.com>
> 
> > Signed-off-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
> > ---
> >  src/compositor.c | 8 +++-----
> >  src/compositor.h | 5 +++--
> >  2 files changed, 6 insertions(+), 7 deletions(-)
> > 
> > diff --git a/src/compositor.c b/src/compositor.c
> > index ee47a82..40d8baf 100644
> > --- a/src/compositor.c
> > +++ b/src/compositor.c
> > @@ -1082,16 +1082,15 @@ weston_surface_update_output_mask(struct weston_surface *es, uint32_t mask)
> >  	}
> >  }
> >  
> > -
> >  /** Recalculate which output(s) the surface has views displayed on
> >   *
> >   * \param es  The surface to remap to outputs
> >   *
> >   * Finds the output that is showing the largest amount of one
> >   * of the surface's various views.  This output becomes the
> > - * surface's primary output for vsync and frame event purposes.
> > + * surface's primary output for vsync and frame callback purposes.
> >   *
> > - * Also notes the primary outputs of all of the surface's views
> > + * Also notes all outputs of all of the surface's views
> >   * in the output_mask for the surface.
> >   */
> >  static void
> > @@ -1136,8 +1135,7 @@ weston_surface_assign_output(struct weston_surface *es)
> >   *
> >   * Identifies the set of outputs that the view is visible on,
> >   * noting them into the output_mask.  The output that the view
> > - * is most visible on is set as the view's primary output for
> > - * vsync and frame event purposes.
> > + * is most visible on is set as the view's primary output.
> >   *
> >   * Also does the same for the view's surface.  See
> >   * weston_surface_assign_output().
> > diff --git a/src/compositor.h b/src/compositor.h
> > index 7851000..0801f20 100644
> > --- a/src/compositor.h
> > +++ b/src/compositor.h
> > @@ -949,8 +949,9 @@ struct weston_view {
> >  	} transform;
> >  
> >  	/*
> > -	 * Which output to vsync this surface to.
> > -	 * Used to determine, whether to send or queue frame events.
> > +	 * The primary output for this view.
> > +	 * Used for picking the output for driving view animations, inheriting
> 
> Is the correct term "driving animations" or "drawing animations" ?

It is actually "driving" here. One surface may be drawn on multiple
outputs, but only one output will "drive" the animation.

Driving the animation means to respond to frame callbacks, and since
outputs may be rendered independently, we tie the animation of a surface
to only one output.

For example: a client rendering an animation will attach and commit a
new buffer of a frame of its animation, and ask for a frame callback.
Then it will wait for the frame callback until it draws, attaches and
commits the buffer of the next frame of its animation.

In order to get as good results as possible, meaning content drawn by
the client should end up on the output as quickly as possible, we
calculate the output it has the largest overlapping region on, and
whenever that output was painted, we reply to the frame callback.

If we for example would wait until all outputs the surface is one is
drawn on until replying, we would potentially delay the frame callback,
making the latency between the client drawing and the content being
displayed on the output, unnecessarily long, since we would effectively
let the output drawn last, no matter how large portion of the surface is
drawn on it, always "drive" the animation.


Jonas

> 
> > +	 * the primary output for related views in shells, etc.
> >  	 * Must be NULL, if 'link' is not in weston_compositor::view_list.
> >  	 */
> >  	struct weston_output *output;
> > 
> 




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