Add outputlocator effect

An effect that implements the "identify" functionality of
the screen configuration kcm. It displays a label on each
screen that identifies the screen.
Doing this as a kwin effect allows to correctly handle
the case when outputs are mirrored (on wayland) compared to
absolute positioning of windows which end up on top of each other.

src/effects/CMakeLists.txt

@@ -76,6 +76,7 @@ add_subdirectory(highlightwindow)
 add_subdirectory(kscreen)
 add_subdirectory(screentransform)
 add_subdirectory(magiclamp)
+add_subdirectory(outputlocator)
 add_subdirectory(overview)
 add_subdirectory(screenedge)
 add_subdirectory(showfps)

src/effects/outputlocator/CMakeLists.txt

@@ -0,0 +1,13 @@
+# SPDX-FileCopyrightText: 2022 David Redondo <kde@david-redondo.de>
+#
+# SPDX-License-Identifier: BSD-3-Clause
+
+
+kwin4_add_effect_module(kwin4_effect_outputlocator main.cpp outputlocator.cpp)
+target_link_libraries(kwin4_effect_outputlocator PRIVATE
+    kwineffects
+    Qt::DBus
+    Qt::Quick
+)
+
+install(DIRECTORY qml DESTINATION ${KDE_INSTALL_DATADIR}/kwin/effects/outputlocator)

src/effects/outputlocator/main.cpp

@@ -0,0 +1,14 @@
+/*
+    SPDX-FileCopyrightText: 2022 David Redondo <kde@david-redondo.de>
+
+    SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+*/
+
+#include "outputlocator.h"
+
+namespace KWin
+{
+KWIN_EFFECT_FACTORY(OutputLocatorEffect, "metadata.json.stripped");
+}
+
+#include "main.moc"

src/effects/outputlocator/metadata.json

@@ -0,0 +1,17 @@
+{
+    "KPlugin": {
+        "Id": "outputlocator",
+        "License": "GPL",
+        "Category": "Appearance",
+        "EnabledByDefault": true,
+        "Authors": [
+            {
+                "Email": "kde@david-redondo.de",
+                "Name": "David Redondo"
+            }
+        ]
+    },
+    "org.kde.kwin.effect": {
+        "internal": true
+    }
+}

src/effects/outputlocator/outputlocator.cpp

@@ -0,0 +1,100 @@
+/*
+    SPDX-FileCopyrightText: 2022 David Redondo <kde@david-redondo.de>
+
+    SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+*/
+
+#include "outputlocator.h"
+
+#include <kwinoffscreenquickview.h>
+#include <main.h>
+
+#include <QApplication>
+#include <QDBusConnection>
+#include <QQuickItem>
+
+namespace KWin
+{
+
+static QString outputName(const EffectScreen *screen)
+{
+    const auto screens = effects->screens();
+    const bool shouldShowSerialNumber = std::any_of(screens.cbegin(), screens.cend(), [screen](const EffectScreen *other) {
+        return other != screen && other->manufacturer() == screen->manufacturer() && other->model() == screen->model();
+    });
+    QString name = screen->manufacturer() + QLatin1Char(' ') + screen->model();
+    if (shouldShowSerialNumber) {
+        name += QLatin1Char(' ') + screen->serialNumber();
+    }
+    return name;
+}
+
+OutputLocatorEffect::OutputLocatorEffect(QObject *parent)
+    : Effect(parent)
+    , m_qmlUrl(QUrl::fromLocalFile(QStandardPaths::locate(QStandardPaths::GenericDataLocation, "kwin/effects/outputlocator/qml/OutputLabel.qml")))
+{
+    QDBusConnection::sessionBus().registerObject(QStringLiteral("/org/kde/KWin/Effect/OutputLocator1"),
+                                                 QStringLiteral("org.kde.KWin.Effect.OutputLocator1"),
+                                                 this,
+                                                 QDBusConnection::ExportAllSlots);
+    connect(&m_showTimer, &QTimer::timeout, this, &OutputLocatorEffect::hide);
+}
+
+bool OutputLocatorEffect::isActive() const
+{
+    return m_showTimer.isActive();
+}
+
+void OutputLocatorEffect::show()
+{
+    if (isActive()) {
+        m_showTimer.start(std::chrono::milliseconds(2500));
+        return;
+    }
+
+    // Needed until Qt6 https://codereview.qt-project.org/c/qt/qtdeclarative/+/361506
+    m_dummyWindow = std::make_unique<QWindow>();
+    m_dummyWindow->create();
+
+    const auto screens = effects->screens();
+    for (const auto screen : screens) {
+        auto scene = new OffscreenQuickScene(this, m_dummyWindow.get());
+        scene->setSource(m_qmlUrl, {{QStringLiteral("outputName"), outputName(screen)}, {QStringLiteral("resolution"), screen->geometry().size()}, {QStringLiteral("scale"), screen->devicePixelRatio()}});
+        QRectF geometry(0, 0, scene->rootItem()->implicitWidth(), scene->rootItem()->implicitHeight());
+        geometry.moveCenter(screen->geometry().center());
+        scene->setGeometry(geometry.toRect());
+        connect(scene, &OffscreenQuickView::repaintNeeded, this, [scene] {
+            effects->addRepaint(scene->geometry());
+        });
+        m_scenesByScreens.insert(screen, scene);
+    }
+
+    m_showTimer.start(std::chrono::milliseconds(2500));
+}
+
+void OutputLocatorEffect::hide()
+{
+    m_showTimer.stop();
+    const QRegion repaintRegion = std::accumulate(m_scenesByScreens.cbegin(), m_scenesByScreens.cend(), QRegion(), [](QRegion region, OffscreenQuickScene *scene) {
+        return region |= scene->geometry();
+    });
+    qDeleteAll(m_scenesByScreens);
+    m_scenesByScreens.clear();
+    effects->addRepaint(repaintRegion);
+}
+
+void OutputLocatorEffect::paintScreen(int mask, const QRegion &region, KWin::ScreenPaintData &data)
+{
+    effects->paintScreen(mask, region, data);
+    // On X11 all screens are painted at once
+    if (effects->waylandDisplay()) {
+        if (auto scene = m_scenesByScreens.value(data.screen())) {
+            effects->renderOffscreenQuickView(scene);
+        }
+    } else {
+        for (auto scene : m_scenesByScreens) {
+            effects->renderOffscreenQuickView(scene);
+        }
+    }
+}
+}

src/effects/outputlocator/outputlocator.h

@@ -0,0 +1,37 @@
+/*
+    SPDX-FileCopyrightText: 2022 David Redondo <kde@david-redondo.de>
+
+    SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+*/
+
+#pragma once
+
+#include <kwineffects.h>
+
+#include <QTimer>
+#include <QWindow>
+
+namespace KWin
+{
+class OffscreenQuickScene;
+
+class OutputLocatorEffect : public KWin::Effect
+{
+    Q_OBJECT
+
+public:
+    explicit OutputLocatorEffect(QObject *parent = nullptr);
+    void paintScreen(int mask, const QRegion &region, KWin::ScreenPaintData &data) override;
+    bool isActive() const override;
+
+public Q_SLOTS:
+    void show();
+    void hide();
+
+private:
+    QUrl m_qmlUrl;
+    QTimer m_showTimer;
+    std::unique_ptr<QWindow> m_dummyWindow;
+    QMap<EffectScreen *, OffscreenQuickScene *> m_scenesByScreens;
+};
+}

src/effects/outputlocator/qml/OutputLabel.qml

@@ -0,0 +1,43 @@
+/*
+    SPDX-FileCopyrightText: 2012 Dan Vratil <dvratil@redhat.com>
+
+    SPDX-License-Identifier: LGPL-2.1-or-later
+*/
+
+import QtQuick 2.1
+import org.kde.plasma.core 2.0 as PlasmaCore
+import org.kde.plasma.components 3.0 as PlasmaComponents3
+
+Rectangle {
+    id: root;
+
+    property string outputName;
+    property size resolution;
+    property double scale;
+
+    color: theme.backgroundColor
+
+    implicitWidth: childrenRect.width + 2 * childrenRect.x
+    implicitHeight: childrenRect.height + 2 * childrenRect.y
+
+    PlasmaComponents3.Label {
+        id: displayName
+        x: units.largeSpacing * 2
+        y: units.largeSpacing
+        font.pointSize: theme.defaultFont.pointSize * 3
+        text: root.outputName;
+        wrapMode: Text.WordWrap;
+        horizontalAlignment: Text.AlignHCenter;
+    }
+
+    PlasmaComponents3.Label {
+        id: modeLabel;
+        anchors {
+            horizontalCenter: displayName.horizontalCenter
+            top: displayName.bottom
+        }
+        text: resolution.width + "x" + resolution.height +
+              (root.scale !== 1 ? "@" + Math.round(root.scale * 100.0) + "%": "")
+        horizontalAlignment: Text.AlignHCenter;
+    }
+}