From 0455fa9ef98966af9979b2fbc36affd5b34ea853 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Fl=C3=B6ser?= <mgraesslin@kde.org>
Date: Thu, 3 Aug 2017 16:31:20 +0200
Subject: [PATCH] Only send active window changes to X11 root window if the X11
 window changed

Summary:
So far KWin always updated the active window property even if the actual
window id hasn't changed. E.g. if a Wayland window was active and another
Wayland window gets activated the window id was and stays 0.

Nevertheless KWin updated the property causing wakeups in X server and
any application listening to property changes on the root window.

Futhermore this situation is an information leak: we leak when a Wayland
window gets activated to X11.

To solve this problem RootInfo caches the active window id and only
updates if it changes.

Test Plan:
Verified with xev -root that the active window does not get
updated needlessly.

Reviewers: #kwin, #plasma

Subscribers: plasma-devel, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D7096
---
 activation.cpp |  2 +-
 netinfo.cpp    | 11 +++++++++++
 netinfo.h      |  5 +++++
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/activation.cpp b/activation.cpp
index 554dfb082b..9ded1a0569 100644
--- a/activation.cpp
+++ b/activation.cpp
@@ -271,7 +271,7 @@ void Workspace::setActiveClient(AbstractClient* c)
     updateStackingOrder(); // e.g. fullscreens have different layer when active/not-active
 
     if (rootInfo()) {
-        rootInfo()->setActiveWindow(active_client ? active_client->window() : 0);
+        rootInfo()->setActiveClient(active_client);
     }
 
     emit clientActivated(active_client);
diff --git a/netinfo.cpp b/netinfo.cpp
index 326f6b1fb5..9da14d63f0 100644
--- a/netinfo.cpp
+++ b/netinfo.cpp
@@ -138,6 +138,7 @@ void RootInfo::destroy()
 RootInfo::RootInfo(xcb_window_t w, const char *name, NET::Properties properties, NET::WindowTypes types,
                    NET::States states, NET::Properties2 properties2, NET::Actions actions, int scr)
     : NETRootInfo(connection(), w, name, properties, types, states, properties2, actions, scr)
+    , m_activeWindow(activeWindow())
 {
 }
 
@@ -224,6 +225,16 @@ void RootInfo::changeShowingDesktop(bool showing)
     Workspace::self()->setShowingDesktop(showing);
 }
 
+void RootInfo::setActiveClient(AbstractClient *client)
+{
+    const xcb_window_t w = client ? client->window() : xcb_window_t{XCB_WINDOW_NONE};
+    if (m_activeWindow == w) {
+        return;
+    }
+    m_activeWindow = w;
+    setActiveWindow(m_activeWindow);
+}
+
 // ****************************************
 // WinInfo
 // ****************************************
diff --git a/netinfo.h b/netinfo.h
index 46a91b1402..b5f8a2e620 100644
--- a/netinfo.h
+++ b/netinfo.h
@@ -30,6 +30,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 namespace KWin
 {
 
+class AbstractClient;
 class Client;
 
 /**
@@ -44,6 +45,8 @@ public:
     static RootInfo *create();
     static void destroy();
 
+    void setActiveClient(AbstractClient *client);
+
 protected:
     virtual void changeNumberOfDesktops(int n) override;
     virtual void changeCurrentDesktop(int d) override;
@@ -60,6 +63,8 @@ private:
              NET::States states, NET::Properties2 properties2, NET::Actions actions, int scr = -1);
     static RootInfo *s_self;
     friend RootInfo *rootInfo();
+
+    xcb_window_t m_activeWindow;
 };
 
 inline RootInfo *rootInfo()