From c9daf4288d92218d9242f91aaf35ee3d5ca5b33a Mon Sep 17 00:00:00 2001
From: reuk <reuk@users.noreply.github.com>
Date: Tue, 21 Sep 2021 13:47:18 +0100
Subject: [PATCH] XWindowSystem:  Only restack sibling windows

Previously, BadMatch errors were seen when there were several modal
windows, each with a native titlebar. Moving a window would attempt to
restack the windows, which was not possible because the JUCE windows
were not siblings. We actually need to restack the top level windows,
i.e. the windows containing the server-side decorations.
---
 .../native/x11/juce_linux_XWindowSystem.cpp   | 29 +++++++++++++++++--
 .../native/x11/juce_linux_XWindowSystem.h     |  2 ++
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/modules/juce_gui_basics/native/x11/juce_linux_XWindowSystem.cpp b/modules/juce_gui_basics/native/x11/juce_linux_XWindowSystem.cpp
index e595d9e527..4e38e7ed82 100644
--- a/modules/juce_gui_basics/native/x11/juce_linux_XWindowSystem.cpp
+++ b/modules/juce_gui_basics/native/x11/juce_linux_XWindowSystem.cpp
@@ -1920,10 +1920,13 @@ void XWindowSystem::toBehind (::Window windowH, ::Window otherWindow) const
 {
     jassert (windowH != 0 && otherWindow != 0);
 
-    Window newStack[] = { otherWindow, windowH };
+    const auto topLevelA = findTopLevelWindowOf (windowH);
+    const auto topLevelB = findTopLevelWindowOf (otherWindow);
+
+    Window newStack[] = { topLevelA, topLevelB };
 
     XWindowSystemUtilities::ScopedXLock xLock;
-    X11Symbols::getInstance()->xRestackWindows (display, newStack, 2);
+    X11Symbols::getInstance()->xRestackWindows (display, newStack, numElementsInArray (newStack));
 }
 
 bool XWindowSystem::isFocused (::Window windowH) const
@@ -2653,6 +2656,28 @@ String XWindowSystem::getTextFromClipboard() const
 }
 
 //==============================================================================
+::Window XWindowSystem::findTopLevelWindowOf (::Window w) const
+{
+    if (w == 0)
+        return 0;
+
+    Window* windowList = nullptr;
+    uint32 windowListSize = 0;
+    Window parent, root;
+
+    XWindowSystemUtilities::ScopedXLock xLock;
+    const auto result = X11Symbols::getInstance()->xQueryTree (display, w, &root, &parent, &windowList, &windowListSize);
+    const auto deleter = makeXFreePtr (windowList);
+
+    if (result == 0)
+        return 0;
+
+    if (parent == root)
+        return w;
+
+    return findTopLevelWindowOf (parent);
+}
+
 bool XWindowSystem::isParentWindowOf (::Window windowH, ::Window possibleChild) const
 {
     if (windowH == 0 || possibleChild == 0)
diff --git a/modules/juce_gui_basics/native/x11/juce_linux_XWindowSystem.h b/modules/juce_gui_basics/native/x11/juce_linux_XWindowSystem.h
index 947eff4661..eefb4b753b 100644
--- a/modules/juce_gui_basics/native/x11/juce_linux_XWindowSystem.h
+++ b/modules/juce_gui_basics/native/x11/juce_linux_XWindowSystem.h
@@ -239,6 +239,8 @@ private:
     void dismissBlockingModals      (LinuxComponentPeer*) const;
     void dismissBlockingModals      (LinuxComponentPeer*, const XConfigureEvent&) const;
 
+    ::Window findTopLevelWindowOf (::Window) const;
+
     static void windowMessageReceive (XEvent&);
 
     //==============================================================================