On Wed, 11 Jul 2018 13:16:18 +0100
Daniel Stone <dani...@collabora.com> wrote:

> a0f8276fe814 ("compositor-drm: Disallow overlapping overlay planes") was
> a little too pessimistic in rejecting occluded views. Whilst it
> correctly prevented overlay planes from occluding each other, it also
> prevented overlay planes from occluding the scanout plane.
> 
> This is undesirable: the primary/scanout plane is specified to stack
> strictly below all overlay planes, so there is no need to reject a plane
> from consideration for scanout due to being occluded by an overlay
> plane.
> 
> Shift the check downwards so it only applies to overlay rather than
> scanout planes.
> 
> Signed-off-by: Daniel Stone <dani...@collabora.com>
> ---
>  libweston/compositor-drm.c | 23 ++++++++++++-----------
>  1 file changed, 12 insertions(+), 11 deletions(-)
> 
> diff --git a/libweston/compositor-drm.c b/libweston/compositor-drm.c
> index d192eec16..3d1847790 100644
> --- a/libweston/compositor-drm.c
> +++ b/libweston/compositor-drm.c
> @@ -3426,17 +3426,6 @@ drm_output_propose_state(struct weston_output 
> *output_base,
>               if (pixman_region32_not_empty(&surface_overlap))
>                       force_renderer = true;
>  
> -             /* We do not control the stacking order of overlay planes;
> -              * the scanout plane is strictly stacked bottom and the cursor
> -              * plane top, but the ordering of overlay planes with respect
> -              * to each other is undefined. Make sure we do not have two
> -              * planes overlapping each other. */
> -             pixman_region32_intersect(&surface_overlap, &occluded_region,
> -                                       &clipped_view);
> -             if (pixman_region32_not_empty(&surface_overlap))
> -                     force_renderer = true;
> -             pixman_region32_fini(&surface_overlap);
> -
>               /* The cursor plane is 'special' in the sense that we can still
>                * place it in the legacy API, and we gate that with a separate
>                * cursors_are_broken flag. */

Does this not introduce a failure mode that we get wrong z-order if an
overlay was supposed to occlude a view that's otherwise eligible for
the cursor plane?


Thanks,
pq

> @@ -3457,6 +3446,18 @@ drm_output_propose_state(struct weston_output 
> *output_base,
>                * scanout plane. */
>               if (!ps && !force_renderer && !renderer_ok)
>                       ps = drm_output_prepare_scanout_view(state, ev, mode);
> +
> +             /* We do not control the stacking order of overlay planes;
> +              * the scanout plane is strictly stacked bottom and the cursor
> +              * plane top, but the ordering of overlay planes with respect
> +              * to each other is undefined. Make sure we do not have two
> +              * planes overlapping each other. */
> +             pixman_region32_intersect(&surface_overlap, &occluded_region,
> +                                       &clipped_view);
> +             if (pixman_region32_not_empty(&surface_overlap))
> +                     force_renderer = true;
> +             pixman_region32_fini(&surface_overlap);
> +
>               if (!ps && !force_renderer)
>                       ps = drm_output_prepare_overlay_view(state, ev, mode);
>  

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