core: Drop OutputBackend::isReady()

OutputBackend has a concept of readiness. When the host compositor goes
down, the OutputBackend will be marked as not ready, and when it
reappears, the output backend will be marked ready again.

On the other hand, host compositor going down is a niche case, it's not
something that often happens and it's hard to justify adding more moving
parts to the startup code. It's easier to call initialize() and check
whether it fails rather than call initialize() and then monitor isReady.

Therefore, this change drops OutputBackend::isReady() to make startup
simpler.

src/backends/drm/drm_backend.cpp

@@ -218,7 +218,6 @@ bool DrmBackend::initialize()
             m_udevMonitor->enable();
         }
     }
-    setReady(true);
     return true;
 }
 

src/backends/virtual/virtual_backend.cpp

@@ -40,7 +40,6 @@ VirtualBackend::~VirtualBackend()
 
 bool VirtualBackend::initialize()
 {
-    setReady(true);
     return true;
 }
 

src/backends/wayland/wayland_backend.cpp

@@ -608,7 +608,6 @@ bool WaylandBackend::initialize()
         m_waylandCursor->init();
     });
 
-    setReady(true);
     return true;
 }
 

src/backends/x11/standalone/x11_standalone_backend.cpp

@@ -128,9 +128,7 @@ X11StandaloneBackend::~X11StandaloneBackend()
     if (sceneEglDisplay() != EGL_NO_DISPLAY) {
         eglTerminate(sceneEglDisplay());
     }
-    if (isReady()) {
-        XRenderUtils::cleanup();
-    }
+    XRenderUtils::cleanup();
 }
 
 bool X11StandaloneBackend::initialize()
@@ -139,7 +137,6 @@ bool X11StandaloneBackend::initialize()
         return false;
     }
     XRenderUtils::init(kwinApp()->x11Connection(), kwinApp()->x11RootWindow());
-    setReady(true);
     initOutputs();
 
     if (Xcb::Extensions::self()->isRandrAvailable()) {

src/backends/x11/windowed/x11_windowed_backend.cpp

@@ -206,7 +206,6 @@ bool X11WindowedBackend::initialize()
             KWin::Cursor *c = KWin::Cursors::self()->currentCursor();
             createCursor(c->image(), c->hotspot());
         });
-        setReady(true);
         m_pointerDevice = std::make_unique<X11WindowedInputDevice>();
         m_pointerDevice->setPointer(true);
         m_keyboardDevice = std::make_unique<X11WindowedInputDevice>();

src/composite.cpp

@@ -141,18 +141,7 @@ Compositor::Compositor(QObject *workspace)
     // The ctor of this class is invoked from the Workspace ctor, that means before
     // Workspace is completely constructed, so calling Workspace::self() would result
     // in undefined behavior. This is fixed by using a delayed invocation.
-    if (kwinApp()->outputBackend()->isReady()) {
-        QTimer::singleShot(0, this, &Compositor::start);
-    }
-    connect(
-        kwinApp()->outputBackend(), &OutputBackend::readyChanged, this, [this](bool ready) {
-            if (ready) {
-                start();
-            } else {
-                stop();
-            }
-        },
-        Qt::QueuedConnection);
+    QTimer::singleShot(0, this, &Compositor::start);
 
     connect(kwinApp(), &Application::x11ConnectionChanged, this, &Compositor::initializeX11);
     connect(kwinApp(), &Application::x11ConnectionAboutToBeDestroyed, this, &Compositor::cleanupX11);

src/core/outputbackend.cpp

@@ -91,15 +91,6 @@ Output *OutputBackend::findOutput(const QString &name) const
     return nullptr;
 }
 
-void OutputBackend::setReady(bool ready)
-{
-    if (m_ready == ready) {
-        return;
-    }
-    m_ready = ready;
-    Q_EMIT readyChanged(m_ready);
-}
-
 Output *OutputBackend::createVirtualOutput(const QString &name, const QSize &size, double scale)
 {
     return nullptr;

src/core/outputbackend.h

@@ -74,10 +74,6 @@ public:
      */
     void setSceneEglGlobalShareContext(EGLContext context);
 
-    bool isReady() const
-    {
-        return m_ready;
-    }
     void setInitialWindowSize(const QSize &size)
     {
         m_initialWindowSize = size;
@@ -135,7 +131,6 @@ public Q_SLOTS:
 
 Q_SIGNALS:
     void outputsQueried();
-    void readyChanged(bool);
     /**
      * This signal is emitted when an output has been connected. The @a output is not ready
      * for compositing yet.
@@ -148,7 +143,6 @@ Q_SIGNALS:
 
 protected:
     explicit OutputBackend(QObject *parent = nullptr);
-    void setReady(bool ready);
     QSize initialWindowSize() const
     {
         return m_initialWindowSize;
@@ -159,7 +153,6 @@ protected:
     }
 
 private:
-    bool m_ready = false;
     QSize m_initialWindowSize;
     QByteArray m_deviceIdentifier;
     int m_initialOutputCount = 1;