[PATCH weston 3/3] compositor-drm: Fix artifacts when scanning out a client buffer

[Kristian Høgsberg]

On Wed, Nov 21, 2012 at 8:11 AM, Ander Conselvan de Oliveira
<ander.conselvan.de.oliveira at intel.com> wrote:
> Consider the following scenario: a fullscreen surface is composited for
> a few frames and suddenly it is moved to a scan out plane. (This could
> happen for instance if it used a big cursor and later switched to a
> cursor that fits in the hw cursor overlay.) If that surface is resized
> during one frame such that it can no longer be scanned out, the
> following frames won't be repainted properly.
>
> The reason for this is that the renderer's repaint function is not
> called if a client buffer is scanned out. When the surface moves to the
> scan out plane, the primary plane is damaged but that damage never hits
> the renderer. When we switch back to compositing, the output back
> buffers are dirty. One of them is updated because of the damage stored
> on the gl renderer per buffer damage for the last composited frame, but
> the other buffer is not redraw.

Ah, I see.  I think the problem instead is that we clear
primary_plane->damage unconditionally in weston_output_repaint, even
if we don't actually paint that damage.  If we move the clearing to
the output repaint vfunc, and only call it when we render, I think
that will solve the problem.

Kristian

> This patch fix this bug by storing all the damage coming from the
> compositor when scanning out a client buffer and feeding that back to
> the renderer once it switches back to compositing.
> ---
>  src/compositor-drm.c |   22 +++++++++++++++++++---
>  1 file changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/src/compositor-drm.c b/src/compositor-drm.c
> index 142faa5..2be903c 100644
> --- a/src/compositor-drm.c
> +++ b/src/compositor-drm.c
> @@ -142,6 +142,7 @@ struct drm_output {
>         int current_cursor;
>         struct drm_fb *current, *next;
>         struct backlight *backlight;
> +       pixman_region32_t pending_damage;
>  };
>
>  /*
> @@ -382,10 +383,21 @@ drm_output_repaint(struct weston_output *output_base,
>         struct drm_mode *mode;
>         int ret = 0;
>
> -       if (!output->next)
> +       if (output->next) {
> +               /* Since the renderer is not going to be called, save this
> +                * damage for later */
> +               pixman_region32_union(&output->pending_damage,
> +                                     &output->pending_damage, damage);
> +       } else {
> +               pixman_region32_union(damage,
> +                                     damage, &output->pending_damage);
> +               pixman_region32_fini(&output->pending_damage);
> +               pixman_region32_init(&output->pending_damage);
> +
>                 drm_output_render(output, damage);
> -       if (!output->next)
> -               return;
> +               if (!output->next)
> +                       return;
> +       }
>
>         mode = container_of(output->base.current, struct drm_mode, base);
>         if (!output->current) {
> @@ -837,6 +849,8 @@ drm_output_destroy(struct weston_output *output_base)
>
>         gbm_surface_destroy(output->surface);
>
> +       pixman_region32_fini(&output->pending_damage);
> +
>         weston_plane_release(&output->fb_plane);
>         weston_plane_release(&output->cursor_plane);
>
> @@ -1404,6 +1418,8 @@ create_output_for_connector(struct drm_compositor *ec,
>         weston_plane_init(&output->cursor_plane, 0, 0);
>         weston_plane_init(&output->fb_plane, 0, 0);
>
> +       pixman_region32_init(&output->pending_damage);
> +
>         weston_log("Output %s, (connector %d, crtc %d)\n",
>                    output->name, output->connector_id, output->crtc_id);
>         wl_list_for_each(m, &output->base.mode_list, link)
> --
> 1.7.10.4
>
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