backends/drm: block input with the placeholder output

This is to prevent the user from accidentally changing application state
while they don't have an output connected

src/backends/drm/CMakeLists.txt

@@ -23,6 +23,7 @@ set(DRM_SOURCES
     drm_buffer_gbm.cpp
     gbm_surface.cpp
     gbm_dmabuf.cpp
+    placeholderinputeventfilter.cpp
 )
 
 add_library(KWinWaylandDrmBackend MODULE ${DRM_SOURCES})

src/backends/drm/drm_backend.cpp

@@ -504,6 +504,7 @@ void DrmBackend::enableOutput(DrmAbstractOutput *output, bool enable)
             qCDebug(KWIN_DRM) << "removing placeholder output";
             primaryGpu()->removeVirtualOutput(m_placeHolderOutput);
             m_placeHolderOutput = nullptr;
+            m_placeholderFilter.reset();
         }
     } else {
         if (m_enabledOutputs.count() == 1 && m_outputs.count() > 1) {
@@ -523,6 +524,8 @@ void DrmBackend::enableOutput(DrmAbstractOutput *output, bool enable)
             m_placeHolderOutput = primaryGpu()->createVirtualOutput({}, m_enabledOutputs.constFirst()->pixelSize(), 1, DrmGpu::Placeholder);
             // placeholder doesn't actually need to render anything
             m_placeHolderOutput->renderLoop()->inhibit();
+            m_placeholderFilter.reset(new PlaceholderInputEventFilter());
+            input()->prependInputEventFilter(m_placeholderFilter.data());
         }
         m_enabledOutputs.removeOne(output);
         Q_EMIT output->gpu()->outputDisabled(output);

src/backends/drm/drm_backend.h

@@ -11,6 +11,7 @@
 #include "platform.h"
 
 #include "dpmsinputeventfilter.h"
+#include "placeholderinputeventfilter.h"
 
 #include <QPointer>
 #include <QSize>
@@ -103,6 +104,7 @@ private:
     const QStringList m_explicitGpus;
     QVector<DrmGpu*> m_gpus;
     QScopedPointer<DpmsInputEventFilter> m_dpmsFilter;
+    QScopedPointer<PlaceholderInputEventFilter> m_placeholderFilter;
 };
 
 

src/backends/drm/placeholderinputeventfilter.cpp

@@ -0,0 +1,57 @@
+/*
+    KWin - the KDE window manager
+    This file is part of the KDE project.
+
+    SPDX-FileCopyrightText: 2022 Xaver Hugl <xaver.hugl@gmail.com>
+
+    SPDX-License-Identifier: GPL-2.0-or-later
+*/
+
+#include "placeholderinputeventfilter.h"
+
+namespace KWin
+{
+
+bool PlaceholderInputEventFilter::pointerEvent(QMouseEvent *event, quint32 nativeButton)
+{
+    Q_UNUSED(event)
+    Q_UNUSED(nativeButton)
+    return true;
+}
+
+bool PlaceholderInputEventFilter::wheelEvent(QWheelEvent *event)
+{
+    Q_UNUSED(event)
+    return true;
+}
+
+bool PlaceholderInputEventFilter::keyEvent(QKeyEvent *event)
+{
+    Q_UNUSED(event)
+    return true;
+}
+
+bool PlaceholderInputEventFilter::touchDown(qint32 id, const QPointF &pos, quint32 time)
+{
+    Q_UNUSED(id)
+    Q_UNUSED(pos)
+    Q_UNUSED(time)
+    return true;
+}
+
+bool PlaceholderInputEventFilter::touchMotion(qint32 id, const QPointF &pos, quint32 time)
+{
+    Q_UNUSED(id)
+    Q_UNUSED(pos)
+    Q_UNUSED(time)
+    return true;
+}
+
+bool PlaceholderInputEventFilter::touchUp(qint32 id, quint32 time)
+{
+    Q_UNUSED(id)
+    Q_UNUSED(time)
+    return true;
+}
+
+}

src/backends/drm/placeholderinputeventfilter.h

@@ -0,0 +1,27 @@
+/*
+    KWin - the KDE window manager
+    This file is part of the KDE project.
+
+    SPDX-FileCopyrightText: 2022 Xaver Hugl <xaver.hugl@gmail.com>
+
+    SPDX-License-Identifier: GPL-2.0-or-later
+*/
+#pragma once
+
+#include "input.h"
+
+namespace KWin
+{
+
+class PlaceholderInputEventFilter : public InputEventFilter
+{
+public:
+    bool pointerEvent(QMouseEvent *event, quint32 nativeButton) override;
+    bool wheelEvent(QWheelEvent *event) override;
+    bool keyEvent(QKeyEvent *event) override;
+    bool touchDown(qint32 id, const QPointF &pos, quint32 time) override;
+    bool touchMotion(qint32 id, const QPointF &pos, quint32 time) override;
+    bool touchUp(qint32 id, quint32 time) override;
+};
+
+}