Introduce Platform::{outputAdded, outputRemoved} signals

These new signals can be useful if you are interested only in when a
specific output gets added or removed.

platform.h

@@ -498,6 +498,8 @@ Q_SIGNALS:
      * Emitted by backends using a one screen (nested window) approach and when the size of that changes.
      */
     void screenSizeChanged();
+    void outputAdded(AbstractOutput *output);
+    void outputRemoved(AbstractOutput *output);
 
 protected:
     explicit Platform(QObject *parent = nullptr);

plugins/platforms/drm/drm_backend.cpp

@@ -332,6 +332,7 @@ void DrmBackend::addOutput(DrmOutput *o)
     m_outputs.append(o);
     m_enabledOutputs.append(o);
     emit o->gpu()->outputEnabled(o);
+    emit outputAdded(o);
 }
 
 void DrmBackend::removeOutput(DrmOutput *o)
@@ -339,6 +340,7 @@ void DrmBackend::removeOutput(DrmOutput *o)
     emit o->gpu()->outputDisabled(o);
     m_outputs.removeOne(o);
     m_enabledOutputs.removeOne(o);
+    emit outputRemoved(o);
 }
 
 bool DrmBackend::updateOutputs()

plugins/platforms/wayland/egl_wayland_backend.cpp

@@ -105,7 +105,7 @@ EglWaylandBackend::EglWaylandBackend(WaylandBackend *b)
 
     connect(m_backend, &WaylandBackend::outputAdded, this, &EglWaylandBackend::createEglWaylandOutput);
     connect(m_backend, &WaylandBackend::outputRemoved, this,
-        [this] (WaylandOutput *output) {
+        [this] (AbstractOutput *output) {
             auto it = std::find_if(m_outputs.begin(), m_outputs.end(),
                 [output] (const EglWaylandOutput *o) {
                     return o->m_waylandOutput == output;
@@ -133,9 +133,9 @@ void EglWaylandBackend::cleanupSurfaces()
     m_outputs.clear();
 }
 
-bool EglWaylandBackend::createEglWaylandOutput(WaylandOutput *waylandOutput)
+bool EglWaylandBackend::createEglWaylandOutput(AbstractOutput *waylandOutput)
 {
-    auto *output = new EglWaylandOutput(waylandOutput, this);
+    auto *output = new EglWaylandOutput(static_cast<WaylandOutput *>(waylandOutput), this);
     if (!output->init(this)) {
         return false;
     }

plugins/platforms/wayland/egl_wayland_backend.h

@@ -87,7 +87,7 @@ private:
     bool initBufferConfigs();
     bool initRenderingContext();
 
-    bool createEglWaylandOutput(WaylandOutput *output);
+    bool createEglWaylandOutput(AbstractOutput *output);
 
     void cleanupSurfaces() override;
     void cleanupOutput(EglWaylandOutput *output);

plugins/platforms/wayland/scene_qpainter_wayland_backend.cpp

@@ -137,7 +137,7 @@ WaylandQPainterBackend::WaylandQPainterBackend(Wayland::WaylandBackend *b)
     }
     connect(m_backend, &WaylandBackend::outputAdded, this, &WaylandQPainterBackend::createOutput);
     connect(m_backend, &WaylandBackend::outputRemoved, this,
-        [this] (WaylandOutput *waylandOutput) {
+        [this] (AbstractOutput *waylandOutput) {
             auto it = std::find_if(m_outputs.begin(), m_outputs.end(),
                 [waylandOutput] (WaylandQPainterOutput *output) {
                     return output->m_waylandOutput == waylandOutput;
@@ -161,9 +161,9 @@ bool WaylandQPainterBackend::perScreenRendering() const
     return true;
 }
 
-void WaylandQPainterBackend::createOutput(WaylandOutput *waylandOutput)
+void WaylandQPainterBackend::createOutput(AbstractOutput *waylandOutput)
 {
-    auto *output = new WaylandQPainterOutput(waylandOutput, this);
+    auto *output = new WaylandQPainterOutput(static_cast<WaylandOutput *>(waylandOutput), this);
     output->init(m_backend->shmPool());
     m_outputs << output;
 }

plugins/platforms/wayland/scene_qpainter_wayland_backend.h

@@ -27,6 +27,7 @@ class Buffer;
 
 namespace KWin
 {
+class AbstractOutput;
 namespace Wayland
 {
 class WaylandBackend;
@@ -79,7 +80,7 @@ public:
     bool perScreenRendering() const override;
 
 private:
-    void createOutput(WaylandOutput *waylandOutput);
+    void createOutput(AbstractOutput *waylandOutput);
     void frameRendered();
 
     WaylandBackend *m_backend;

plugins/platforms/wayland/wayland_backend.h

@@ -203,9 +203,6 @@ public:
     }
 
 Q_SIGNALS:
-    void outputAdded(WaylandOutput *output);
-    void outputRemoved(WaylandOutput *output);
-
     void systemCompositorDied();
     void connectionFailed();