[Mesa-dev] [PATCH 1/2] glx: Ensure that glXWaitX actually waits for X.

[Fredrik Höglund]

On Tuesday 07 May 2013, Eric Anholt wrote:
> Ever since fake front was introduced in
> 63b51b5cf17ddde09b72a2811296f37b9a4c5ad2, we were skipping the XSync() in
> the non-fake-front path, so compositors like Firefox's GL canvas were
> having to manually put it in outside of glXWaitX().
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=52930
> ---
>  src/glx/dri2_glx.c | 21 +++++++++++++++++----
>  1 file changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/src/glx/dri2_glx.c b/src/glx/dri2_glx.c
> index 7ce5775..3cdd249 100644
> --- a/src/glx/dri2_glx.c
> +++ b/src/glx/dri2_glx.c
> @@ -639,10 +639,23 @@ dri2_wait_x(struct glx_context *gc)
>     struct dri2_drawable *priv = (struct dri2_drawable *)
>        GetGLXDRIDrawable(gc->currentDpy, gc->currentDrawable);
>  
> -   if (priv == NULL || !priv->have_fake_front)
> -      return;
> -
> -   dri2_copy_drawable(priv, DRI2BufferFakeFrontLeft, DRI2BufferFrontLeft);
> +   if (priv != NULL && priv->have_fake_front) {
> +      /* Ask the server to update our copy of the front buffer from the real
> +       * front buffer.  This will round-trip with the server, so we can skip
> +       * the XSync().
> +       */
> +      dri2_copy_drawable(priv, DRI2BufferFakeFrontLeft, DRI2BufferFrontLeft);
> +   } else {
> +      /* From the GLX 1.4 spec, page 33:
> +       *
> +       *     "X rendering calls made prior to glXWaitX are guaranteed to be
> +       *      executed before OpenGL rendering calls made after
> +       *      glXWaitX. While the same result can be achieved using XSync,
> +       *      glXWaitX does not require a round trip to the server, and may
> +       *      therefore be more efficient."
> +       */
> +      XSync(gc->currentDpy, False);

I think this could be improved a bit by calling xcb_get_input_focus() followed
by xcb_flush() here, and forcing the reply the next time the command buffer
is about to be flushed.

Fredrik