From ba2c0324d2ef21a5c42ec182e851a435180b51ac Mon Sep 17 00:00:00 2001
From: Roman Gilg <subdiff@gmail.com>
Date: Wed, 18 Dec 2019 21:25:48 +0100
Subject: Reset buffer swap state on stop

Summary:
When the compositor is stopped there might still be a buffer swap ongoing, in
particular when a client blocks compositing on X11.

Depending on the backend the next buffer swap event might be handled in
bufferSwapComplete (Wayland) or not be handled (X11 GLX, since a new
GLX window will be created while the swap event is sent for the old one).

With this patch the buffer swap state is reset on stop such that on later
start no outdated data might create errors  and instead a new repaint can be
triggered with updated data.

BUG: 415262

Test Plan: Manually on X11 and Wayland.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D26090

--- a/composite.cpp	2020-05-03 00:37:29.000000000 +0300
+++ b/composite.cpp	2020-05-03 00:45:28.824084430 +0300
@@ -451,6 +451,8 @@
 
     delete m_scene;
     m_scene = nullptr;
+    m_bufferSwapPending = false;
+    m_composeAtSwapCompletion = false;
     compositeTimer.stop();
     repaints_region = QRegion();
 
@@ -719,11 +721,8 @@
     // is called the next time. If there would be nothing pending, it will not restart the timer and
     // scheduleRepaint() would restart it again somewhen later, called from functions that
     // would again add something pending.
-    if (m_bufferSwapPending && m_scene->syncsToVBlank()) {
-        m_composeAtSwapCompletion = true;
-    } else {
-        scheduleRepaint();
-    }
+    Q_ASSERT(!m_bufferSwapPending);
+    scheduleRepaint();
 }
 
 template <class T>