[PATCH] Flush the wl_display at the end of SwapBuffers

Neil Roberts neil at linux.intel.com
Wed Dec 4 06:36:05 PST 2013

I think this is a good idea. Imagine a simple game main loop like this:

while (TRUE) {

In that case it wouldn't flush the commit until the right at the
beginning of each call to eglSwapBuffers when it waits for the frame
callback. Then it would have to block waiting for the compositor to
finish rendering before it receives the frame callback. If we dispatch
after the swap buffers then in this case the compositor could start
rendering while the game is in do_some_game_logic().

There was a similar patch proposed on the Mesa-dev mailing list here:


That also points out the additional problem case where the rendering is
done in a separate thread. After the rendering is done potentially
nothing would wake up the main loop thread and cause a dispatch.

That patch also moves the call to dri2_dpy->flush->flush further up. I'm
not sure if that is necessary. It also adds a pointer to the wl_display
in struct dri2_egl_surface which definitely looks unnecessary. So I
think Axel's patch makes more sense.

Reviewed-by: Neil Roberts <neil at linux.intel.com>

- Neil

Axel Davy <axel.davy at ens.fr> writes:

> We would like the compositor to receive the commited buffer
> as soon as possible, so it has the time to treat it, and 
> release old ones. We shouldn't rely on the client
> to flush the queue for us.
> Signed-off-by: Axel Davy <axel.davy at ens.fr>
> ---
> We flush the wl_display after we flush the drawable.
>  src/egl/drivers/dri2/platform_wayland.c | 2 ++
>  1 file changed, 2 insertions(+)
> diff --git a/src/egl/drivers/dri2/platform_wayland.c b/src/egl/drivers/dri2/platform_wayland.c
> index 7e3733b..8c3d1f1 100644
> --- a/src/egl/drivers/dri2/platform_wayland.c
> +++ b/src/egl/drivers/dri2/platform_wayland.c
> @@ -627,6 +627,8 @@ dri2_swap_buffers_with_damage(_EGLDriver *drv,
>        (*dri2_dpy->flush->flush)(dri2_surf->dri_drawable);
>     (*dri2_dpy->flush->invalidate)(dri2_surf->dri_drawable);
> +   wl_display_flush(dri2_dpy->wl_dpy);
> +
>     return EGL_TRUE;
>  }
> -- 
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