core: Drop Platform::supportsGammaControl()

If the platform doesn't support setting gamma ramps, let the request
fail. In long term, we need a software fallback too so this property is
not that relevant.

src/backends/drm/drm_backend.cpp

@@ -77,7 +77,6 @@ DrmBackend::DrmBackend(Session *session, QObject *parent)
     , m_explicitGpus(splitPathList(qEnvironmentVariable("KWIN_DRM_DEVICES"), ':'))
     , m_dpmsFilter()
 {
-    setSupportsGammaControl(true);
 }
 
 DrmBackend::~DrmBackend() = default;

src/backends/virtual/virtual_backend.cpp

@@ -29,8 +29,6 @@ VirtualBackend::VirtualBackend(QObject *parent)
             qDebug() << "Screenshots saved to: " << m_screenshotDir->path();
         }
     }
-
-    setSupportsGammaControl(true);
 }
 
 VirtualBackend::~VirtualBackend()

src/backends/x11/standalone/x11_standalone_platform.cpp

@@ -121,8 +121,6 @@ X11StandalonePlatform::X11StandalonePlatform(QObject *parent)
     connect(m_updateOutputsTimer.get(), &QTimer::timeout, this, &X11StandalonePlatform::updateOutputs);
 
     m_keyboard = std::make_unique<X11Keyboard>();
-
-    setSupportsGammaControl(true);
 }
 
 X11StandalonePlatform::~X11StandalonePlatform()

src/core/platform.h

@@ -188,15 +188,6 @@ public:
      */
     virtual QVector<CompositingType> supportedCompositors() const = 0;
 
-    /**
-     * Whether gamma control is supported by the backend.
-     * @since 5.12
-     */
-    bool supportsGammaControl() const
-    {
-        return m_supportsGammaControl;
-    }
-
     virtual Outputs outputs() const = 0;
     Output *findOutput(const QString &name) const;
 
@@ -244,10 +235,6 @@ protected:
     {
         return m_deviceIdentifier;
     }
-    void setSupportsGammaControl(bool set)
-    {
-        m_supportsGammaControl = set;
-    }
 
 private:
     bool m_ready = false;
@@ -257,7 +244,6 @@ private:
     qreal m_initialOutputScale = 1;
     EGLDisplay m_eglDisplay;
     EGLContext m_globalShareContext = EGL_NO_CONTEXT;
-    bool m_supportsGammaControl = false;
 };
 
 } // namespace KWin

src/plugins/nightcolor/nightcolordbusinterface.cpp

@@ -193,7 +193,7 @@ bool NightColorDBusInterface::isRunning() const
 
 bool NightColorDBusInterface::isAvailable() const
 {
-    return m_manager->isAvailable();
+    return true; // TODO: Night color should register its own dbus service instead.
 }
 
 int NightColorDBusInterface::currentTemperature() const

src/plugins/nightcolor/nightcolormanager.cpp

@@ -80,10 +80,6 @@ NightColorManager::NightColorManager()
     // we may always read in the current config
     readConfig();
 
-    if (!isAvailable()) {
-        return;
-    }
-
     // legacy shortcut with localized key (to avoid breaking existing config)
     if (i18n("Toggle Night Color") != QStringLiteral("Toggle Night Color")) {
         QAction toggleActionLegacy;
@@ -150,7 +146,7 @@ void NightColorManager::hardReset()
     updateTransitionTimings(true);
     updateTargetTemperature();
 
-    if (isAvailable() && isEnabled() && !isInhibited()) {
+    if (isEnabled() && !isInhibited()) {
         setRunning(true);
         commitGammaRamps(currentTargetTemp());
     }
@@ -205,11 +201,6 @@ bool NightColorManager::isRunning() const
     return m_running;
 }
 
-bool NightColorManager::isAvailable() const
-{
-    return kwinApp()->platform()->supportsGammaControl();
-}
-
 int NightColorManager::currentTemperature() const
 {
     return m_currentTemp;
@@ -312,15 +303,11 @@ void NightColorManager::readConfig()
 void NightColorManager::resetAllTimers()
 {
     cancelAllTimers();
-    if (isAvailable()) {
-        setRunning(isEnabled() && !isInhibited());
-        // we do this also for active being false in order to reset the temperature back to the day value
-        updateTransitionTimings(false);
-        updateTargetTemperature();
-        resetQuickAdjustTimer(currentTargetTemp());
-    } else {
-        setRunning(false);
-    }
+    setRunning(isEnabled() && !isInhibited());
+    // we do this also for active being false in order to reset the temperature back to the day value
+    updateTransitionTimings(false);
+    updateTargetTemperature();
+    resetQuickAdjustTimer(currentTargetTemp());
 }
 
 void NightColorManager::cancelAllTimers()

src/plugins/nightcolor/nightcolormanager.h

@@ -129,11 +129,6 @@ public:
      */
     bool isRunning() const;
 
-    /**
-     * Returns @c true if Night Color is supported by platform; otherwise @c false.
-     */
-    bool isAvailable() const;
-
     /**
      * Returns the current screen color temperature.
      */