From 38ce05eaff4f7f9f63d0b1b6f0ca5270370c2f88 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Fl=C3=B6ser?= <mgraesslin@kde.org>
Date: Sun, 24 Sep 2017 11:00:16 +0200
Subject: [PATCH] Drop the ObscurringWindow functionality on desktop switching

Summary:
The ObscurringWindows are a hack to make it more unlikely that the
desktop wallpaper becomes visible while switching desktops. This was
introduced in 2001 with SVN revision 90111
(git d194f74314285932eb72e1dfecd2816b63647e4e).

In 2001 desktop switching was probably a costly action where it was not
possible to just reorder the desktop in one frame. Nowadays we use
mostly compositing and with compositing the ObscurringWindows are
already disabled. But even in the case that no compositing is used I
consider it as very unlikely that the desktop becomes visible during the
switching. Given that I think it's time to remove this legacy solution.

Test Plan: Compiles

Reviewers: #kwin, #plasma

Subscribers: plasma-devel, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D7965
---
 workspace.cpp | 61 ---------------------------------------------------
 1 file changed, 61 deletions(-)

diff --git a/workspace.cpp b/workspace.cpp
index ebd660d4f9..c1b3816865 100644
--- a/workspace.cpp
+++ b/workspace.cpp
@@ -843,60 +843,6 @@ void Workspace::slotReconfigure()
     }
 }
 
-/**
- * During virt. desktop switching, desktop areas covered by windows that are
- * going to be hidden are first obscured by new windows with no background
- * ( i.e. transparent ) placed right below the windows. These invisible windows
- * are removed after the switch is complete.
- * Reduces desktop ( wallpaper ) repaints during desktop switching
- */
-class ObscuringWindows
-{
-public:
-    ~ObscuringWindows();
-    void create(Client* c);
-private:
-    QList<xcb_window_t> obscuring_windows;
-    static QList<xcb_window_t>* cached;
-    static unsigned int max_cache_size;
-};
-
-QList<xcb_window_t>* ObscuringWindows::cached = nullptr;
-unsigned int ObscuringWindows::max_cache_size = 0;
-
-void ObscuringWindows::create(Client* c)
-{
-    if (!cached)
-        cached = new QList<xcb_window_t>;
-    Xcb::Window obs_win(XCB_WINDOW_NONE, false);
-    if (cached->count() > 0) {
-        obs_win.reset(cached->first(), false);
-        cached->removeAll(obs_win);
-        obs_win.setGeometry(c->geometry());
-    } else {
-        uint32_t values[] = {XCB_PIXMAP_NONE, true};
-        obs_win.create(c->geometry(), XCB_WINDOW_CLASS_INPUT_OUTPUT, XCB_CW_BACK_PIXMAP | XCB_CW_OVERRIDE_REDIRECT, values);
-    }
-    uint32_t values[] = {c->frameId(), XCB_STACK_MODE_BELOW};
-    xcb_configure_window(connection(), obs_win, XCB_CONFIG_WINDOW_SIBLING | XCB_CONFIG_WINDOW_STACK_MODE, values);
-    obs_win.map();
-    obscuring_windows.append(obs_win);
-}
-
-ObscuringWindows::~ObscuringWindows()
-{
-    max_cache_size = qMax(int(max_cache_size), obscuring_windows.count() + 4) - 1;
-    for (auto it = obscuring_windows.constBegin();
-            it != obscuring_windows.constEnd();
-            ++it) {
-        xcb_unmap_window(connection(), *it);
-        if (cached->count() < int(max_cache_size))
-            cached->prepend(*it);
-        else
-            xcb_destroy_window(connection(), *it);
-    }
-}
-
 void Workspace::slotCurrentDesktopChanged(uint oldDesktop, uint newDesktop)
 {
     closeActivePopup();
@@ -912,7 +858,6 @@ void Workspace::slotCurrentDesktopChanged(uint oldDesktop, uint newDesktop)
 
 void Workspace::updateClientVisibilityOnDesktopChange(uint oldDesktop, uint newDesktop)
 {
-    ObscuringWindows obs_wins;
     for (ToplevelList::ConstIterator it = stacking_order.constBegin();
             it != stacking_order.constEnd();
             ++it) {
@@ -921,8 +866,6 @@ void Workspace::updateClientVisibilityOnDesktopChange(uint oldDesktop, uint newD
             continue;
         }
         if (!c->isOnDesktop(newDesktop) && c != movingClient && c->isOnCurrentActivity()) {
-            if (c->isShown(true) && c->isOnDesktop(oldDesktop) && !compositing())
-                obs_wins.create(c);
             (c)->updateVisibility();
         }
     }
@@ -1026,8 +969,6 @@ void Workspace::updateCurrentActivity(const QString &new_activity)
     // mapping done from front to back => less exposure events
     //Notify::raise((Notify::Event) (Notify::DesktopChange+new_desktop));
 
-    ObscuringWindows obs_wins;
-
     const QString &old_activity = Activities::self()->previous();
 
     for (ToplevelList::ConstIterator it = stacking_order.constBegin();
@@ -1038,8 +979,6 @@ void Workspace::updateCurrentActivity(const QString &new_activity)
             continue;
         }
         if (!c->isOnActivity(new_activity) && c != movingClient && c->isOnCurrentDesktop()) {
-            if (c->isShown(true) && c->isOnActivity(old_activity) && !compositing())
-                obs_wins.create(c);
             c->updateVisibility();
         }
     }