[PATCH] Xwayland: fix output changes not getting applied in some, cases

[Ferdi265]

Hello,

I investigated a bug I encountered while using the Sway Compositor and
traced it back to some behaviour in Xwayland:

The xdg_output and wl_output events are handled in such a way that
output changes (e.g. position) sometimes don't get applied if only
xdg_output is sent instead of both xdg_output and wl_output. (Sway does
this)

Below I attached a patch that fixes this. I am not very familiar with
the Xorg codebase, so I hope this patch is fine.

Here (https://github.com/swaywm/sway/issues/4064) is the Sway bug report
in question.

Kind Regards,
Ferdinand "Ferdi265" Bachmann

--- PATCH BELOW ---

From 431a176c112d373a07b861fdf95766b3741ba95c Mon Sep 17 00:00:00 2001
From: Ferdinand Bachmann <theferdi265 at gmail.com>
Date: Mon, 22 Apr 2019 00:35:41 +0200
Subject: [PATCH] Xwayland: fix output changes not getting applied in
some cases

On some wayland compositors wl_output and xdg_output events don't
neccessarily happen together, so waiting until the wl_output event is
done might wait indefinitely.

This fixes output changes not getting applied on newer wlroots-based
compositors, such as sway.

Since these event's don't always happen together, the changes need to
be applied regardless of whether the other event is finished or not,
making the wl_output_done and xdg_output_done flags redundant.
---
 hw/xwayland/xwayland-output.c | 17 ++---------------
 hw/xwayland/xwayland.h        |  2 --
 2 files changed, 2 insertions(+), 17 deletions(-)

diff --git a/hw/xwayland/xwayland-output.c b/hw/xwayland/xwayland-output.c
index cc68f0340..497e56db4 100644
--- a/hw/xwayland/xwayland-output.c
+++ b/hw/xwayland/xwayland-output.c
@@ -218,10 +218,6 @@ apply_output_change(struct xwl_output *xwl_output)
     RRModePtr randr_mode;
     Bool need_rotate;

-    /* Clear out the "done" received flags */
-    xwl_output->wl_output_done = FALSE;
-    xwl_output->xdg_output_done = FALSE;
-
     /* xdg-output sends output size in compositor space. so already
rotated */
     need_rotate = (xwl_output->xdg_output == NULL);

@@ -268,13 +264,7 @@ static void
 output_handle_done(void *data, struct wl_output *wl_output)
 {
     struct xwl_output *xwl_output = data;
-
-    xwl_output->wl_output_done = TRUE;
-    /* Apply the changes from wl_output only if both "done" events are
received,
-     * or if xdg-output is not supported.
-     */
-    if (xwl_output->xdg_output_done || !xwl_output->xdg_output)
-        apply_output_change(xwl_output);
+    apply_output_change(xwl_output);
 }

 static void
@@ -313,10 +303,7 @@ static void
 xdg_output_handle_done(void *data, struct zxdg_output_v1 *xdg_output)
 {
     struct xwl_output *xwl_output = data;
-
-    xwl_output->xdg_output_done = TRUE;
-    if (xwl_output->wl_output_done)
-        apply_output_change(xwl_output);
+    apply_output_change(xwl_output);
 }

 static const struct zxdg_output_v1_listener xdg_output_listener = {
diff --git a/hw/xwayland/xwayland.h b/hw/xwayland/xwayland.h
index 92664e812..1ab2f04b5 100644
--- a/hw/xwayland/xwayland.h
+++ b/hw/xwayland/xwayland.h
@@ -371,8 +371,6 @@ struct xwl_output {
     RRCrtcPtr randr_crtc;
     int32_t x, y, width, height, refresh;
     Rotation rotation;
-    Bool wl_output_done;
-    Bool xdg_output_done;
 };

 void xwl_sync_events (struct xwl_screen *xwl_screen);
-- 
2.21.0

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