core/region: add per-corner radius support

QTextStream is not thread safe.

changelog/next.md

@@ -27,6 +27,8 @@ set shell id.
 - Added a way to detect if an icon is from the system icon theme or not.
 - Added vulkan support to screencopy.
 - Added generic WindowManager interface implementing ext-workspace.
+- Added ext-background-effect window blur support.
+- Added per-corner radius support to Region.
 
 ## Other Changes
 
@@ -38,6 +40,7 @@ set shell id.
 - Added `QS_DISABLE_FILE_WATCHER` environment variable to disable file watching.
 - Added `QS_DISABLE_CRASH_HANDLER` environment variable to disable crash handling.
 - Added `QS_CRASHREPORT_URL` environment variable to allow overriding the crash reporter link.
+- Added `AppId` pragma and `QS_APP_ID` environment variable to allow overriding the desktop application ID.
 
 ## Bug Fixes
 

src/core/instanceinfo.cpp

@@ -3,14 +3,14 @@
 #include <qdatastream.h>
 
 QDataStream& operator<<(QDataStream& stream, const InstanceInfo& info) {
-	stream << info.instanceId << info.configPath << info.shellId << info.launchTime << info.pid
+	stream << info.instanceId << info.configPath << info.shellId << info.appId << info.launchTime
-	       << info.display;
+	       << info.pid << info.display;
 	return stream;
 }
 
 QDataStream& operator>>(QDataStream& stream, InstanceInfo& info) {
-	stream >> info.instanceId >> info.configPath >> info.shellId >> info.launchTime >> info.pid
+	stream >> info.instanceId >> info.configPath >> info.shellId >> info.appId >> info.launchTime
-	    >> info.display;
+	    >> info.pid >> info.display;
 	return stream;
 }
 

src/core/instanceinfo.hpp

@@ -9,6 +9,7 @@ struct InstanceInfo {
 	QString instanceId;
 	QString configPath;
 	QString shellId;
+	QString appId;
 	QDateTime launchTime;
 	pid_t pid = -1;
 	QString display;

src/core/logging.cpp

@@ -14,6 +14,7 @@
 #include <qlist.h>
 #include <qlogging.h>
 #include <qloggingcategory.h>
+#include <qmutex.h>
 #include <qnamespace.h>
 #include <qobject.h>
 #include <qobjectdefs.h>
@@ -220,6 +221,7 @@ void LogManager::messageHandler(
 	}
 
 	if (display) {
+		auto locker = QMutexLocker(&self->stdoutMutex);
 		LogMessage::formatMessage(
 		    self->stdoutStream,
 		    message,

src/core/logging.hpp

@@ -10,6 +10,7 @@
 #include <qlatin1stringview.h>
 #include <qlogging.h>
 #include <qloggingcategory.h>
+#include <qmutex.h>
 #include <qobject.h>
 #include <qtmetamacros.h>
 
@@ -135,6 +136,7 @@ private:
 	QHash<QLatin1StringView, CategoryFilter> allFilters;
 
 	QTextStream stdoutStream;
+	QMutex stdoutMutex;
 	LoggingThreadProxy threadProxy;
 
 	friend void initLogCategoryLevel(const char* name, QtMsgType defaultLevel);

src/core/region.cpp

@@ -1,4 +1,5 @@
 #include "region.hpp"
+#include <algorithm>
 #include <cmath>
 
 #include <qobject.h>
@@ -18,6 +19,11 @@ PendingRegion::PendingRegion(QObject* parent): QObject(parent) {
 	QObject::connect(this, &PendingRegion::yChanged, this, &PendingRegion::changed);
 	QObject::connect(this, &PendingRegion::widthChanged, this, &PendingRegion::changed);
 	QObject::connect(this, &PendingRegion::heightChanged, this, &PendingRegion::changed);
+	QObject::connect(this, &PendingRegion::radiusChanged, this, &PendingRegion::changed);
+	QObject::connect(this, &PendingRegion::topLeftRadiusChanged, this, &PendingRegion::changed);
+	QObject::connect(this, &PendingRegion::topRightRadiusChanged, this, &PendingRegion::changed);
+	QObject::connect(this, &PendingRegion::bottomLeftRadiusChanged, this, &PendingRegion::changed);
+	QObject::connect(this, &PendingRegion::bottomRightRadiusChanged, this, &PendingRegion::changed);
 	QObject::connect(this, &PendingRegion::childrenChanged, this, &PendingRegion::changed);
 }
 
@@ -45,6 +51,79 @@ void PendingRegion::onItemDestroyed() { this->mItem = nullptr; }
 
 void PendingRegion::onChildDestroyed() { this->mRegions.removeAll(this->sender()); }
 
+qint32 PendingRegion::radius() const { return this->mRadius; }
+
+void PendingRegion::setRadius(qint32 radius) {
+	if (radius == this->mRadius) return;
+	this->mRadius = radius;
+	emit this->radiusChanged();
+
+	if (!(this->mCornerOverrides & TopLeft)) emit this->topLeftRadiusChanged();
+	if (!(this->mCornerOverrides & TopRight)) emit this->topRightRadiusChanged();
+	if (!(this->mCornerOverrides & BottomLeft)) emit this->bottomLeftRadiusChanged();
+	if (!(this->mCornerOverrides & BottomRight)) emit this->bottomRightRadiusChanged();
+}
+
+qint32 PendingRegion::topLeftRadius() const {
+	return (this->mCornerOverrides & TopLeft) ? this->mTopLeftRadius : this->mRadius;
+}
+
+void PendingRegion::setTopLeftRadius(qint32 radius) {
+	this->mTopLeftRadius = radius;
+	this->mCornerOverrides |= TopLeft;
+	emit this->topLeftRadiusChanged();
+}
+
+void PendingRegion::resetTopLeftRadius() {
+	this->mCornerOverrides &= ~TopLeft;
+	emit this->topLeftRadiusChanged();
+}
+
+qint32 PendingRegion::topRightRadius() const {
+	return (this->mCornerOverrides & TopRight) ? this->mTopRightRadius : this->mRadius;
+}
+
+void PendingRegion::setTopRightRadius(qint32 radius) {
+	this->mTopRightRadius = radius;
+	this->mCornerOverrides |= TopRight;
+	emit this->topRightRadiusChanged();
+}
+
+void PendingRegion::resetTopRightRadius() {
+	this->mCornerOverrides &= ~TopRight;
+	emit this->topRightRadiusChanged();
+}
+
+qint32 PendingRegion::bottomLeftRadius() const {
+	return (this->mCornerOverrides & BottomLeft) ? this->mBottomLeftRadius : this->mRadius;
+}
+
+void PendingRegion::setBottomLeftRadius(qint32 radius) {
+	this->mBottomLeftRadius = radius;
+	this->mCornerOverrides |= BottomLeft;
+	emit this->bottomLeftRadiusChanged();
+}
+
+void PendingRegion::resetBottomLeftRadius() {
+	this->mCornerOverrides &= ~BottomLeft;
+	emit this->bottomLeftRadiusChanged();
+}
+
+qint32 PendingRegion::bottomRightRadius() const {
+	return (this->mCornerOverrides & BottomRight) ? this->mBottomRightRadius : this->mRadius;
+}
+
+void PendingRegion::setBottomRightRadius(qint32 radius) {
+	this->mBottomRightRadius = radius;
+	this->mCornerOverrides |= BottomRight;
+	emit this->bottomRightRadiusChanged();
+}
+
+void PendingRegion::resetBottomRightRadius() {
+	this->mCornerOverrides &= ~BottomRight;
+	emit this->bottomRightRadiusChanged();
+}
+
 QQmlListProperty<PendingRegion> PendingRegion::regions() {
 	return QQmlListProperty<PendingRegion>(
 	    this,
@@ -90,6 +169,60 @@ QRegion PendingRegion::build() const {
 		region = QRegion(this->mX, this->mY, this->mWidth, this->mHeight, type);
 	}
 
+	if (this->mShape == RegionShape::Rect && !region.isEmpty()) {
+		auto tl = std::max(this->topLeftRadius(), 0);
+		auto tr = std::max(this->topRightRadius(), 0);
+		auto bl = std::max(this->bottomLeftRadius(), 0);
+		auto br = std::max(this->bottomRightRadius(), 0);
+
+		if (tl > 0 || tr > 0 || bl > 0 || br > 0) {
+			auto rect = region.boundingRect();
+			auto x = rect.x();
+			auto y = rect.y();
+			auto w = rect.width();
+			auto h = rect.height();
+
+			// Normalize so adjacent corners don't exceed their shared edge.
+			// Each corner is scaled by the tightest constraint of its two edges.
+			auto topScale = tl + tr > w ? static_cast<double>(w) / (tl + tr) : 1.0;
+			auto bottomScale = bl + br > w ? static_cast<double>(w) / (bl + br) : 1.0;
+			auto leftScale = tl + bl > h ? static_cast<double>(h) / (tl + bl) : 1.0;
+			auto rightScale = tr + br > h ? static_cast<double>(h) / (tr + br) : 1.0;
+
+			tl = static_cast<qint32>(tl * std::min(topScale, leftScale));
+			tr = static_cast<qint32>(tr * std::min(topScale, rightScale));
+			bl = static_cast<qint32>(bl * std::min(bottomScale, leftScale));
+			br = static_cast<qint32>(br * std::min(bottomScale, rightScale));
+
+			// Unlock each corner: subtract (cornerBox - quarterEllipse) from the
+			// full rect. Each corner only modifies pixels inside its own box,
+			// so no diagonal overlap is possible.
+			if (tl > 0) {
+				auto box = QRegion(x, y, tl, tl);
+				auto ellipse = QRegion(x, y, tl * 2, tl * 2, QRegion::Ellipse);
+				region -= box - (ellipse & box);
+			}
+
+			if (tr > 0) {
+				auto box = QRegion(x + w - tr, y, tr, tr);
+				auto ellipse = QRegion(x + w - tr * 2, y, tr * 2, tr * 2, QRegion::Ellipse);
+				region -= box - (ellipse & box);
+			}
+
+			if (bl > 0) {
+				auto box = QRegion(x, y + h - bl, bl, bl);
+				auto ellipse = QRegion(x, y + h - bl * 2, bl * 2, bl * 2, QRegion::Ellipse);
+				region -= box - (ellipse & box);
+			}
+
+			if (br > 0) {
+				auto box = QRegion(x + w - br, y + h - br, br, br);
+				auto ellipse = QRegion(x + w - br * 2, y + h - br * 2, br * 2, br * 2, QRegion::Ellipse);
+				region -= box - (ellipse & box);
+			}
+		}
+	}
+
 	for (const auto& childRegion: this->mRegions) {
 		region = childRegion->applyTo(region);
 	}

src/core/region.hpp

@@ -66,6 +66,29 @@ class PendingRegion: public QObject {
 	Q_PROPERTY(qint32 width MEMBER mWidth NOTIFY widthChanged);
 	/// Defaults to 0. Does nothing if @@item is set.
 	Q_PROPERTY(qint32 height MEMBER mHeight NOTIFY heightChanged);
+	// clang-format off
+	/// Corner radius for rounded rectangles. Only applies when @@shape is `Rect`. Defaults to 0.
+	///
+	/// Acts as the default for @@topLeftRadius, @@topRightRadius, @@bottomLeftRadius,
+	/// and @@bottomRightRadius.
+	Q_PROPERTY(qint32 radius READ radius WRITE setRadius NOTIFY radiusChanged);
+	/// Top-left corner radius. Only applies when @@shape is `Rect`.
+	///
+	/// Defaults to @@radius, and may be reset by assigning `undefined`.
+	Q_PROPERTY(qint32 topLeftRadius READ topLeftRadius WRITE setTopLeftRadius RESET resetTopLeftRadius NOTIFY topLeftRadiusChanged);
+	/// Top-right corner radius. Only applies when @@shape is `Rect`.
+	///
+	/// Defaults to @@radius, and may be reset by assigning `undefined`.
+	Q_PROPERTY(qint32 topRightRadius READ topRightRadius WRITE setTopRightRadius RESET resetTopRightRadius NOTIFY topRightRadiusChanged);
+	/// Bottom-left corner radius. Only applies when @@shape is `Rect`.
+	///
+	/// Defaults to @@radius, and may be reset by assigning `undefined`.
+	Q_PROPERTY(qint32 bottomLeftRadius READ bottomLeftRadius WRITE setBottomLeftRadius RESET resetBottomLeftRadius NOTIFY bottomLeftRadiusChanged);
+	/// Bottom-right corner radius. Only applies when @@shape is `Rect`.
+	///
+	/// Defaults to @@radius, and may be reset by assigning `undefined`.
+	Q_PROPERTY(qint32 bottomRightRadius READ bottomRightRadius WRITE setBottomRightRadius RESET resetBottomRightRadius NOTIFY bottomRightRadiusChanged);
+	// clang-format on
 
 	/// Regions to apply on top of this region.
 	///
@@ -91,6 +114,25 @@ public:
 
 	void setItem(QQuickItem* item);
 
+	[[nodiscard]] qint32 radius() const;
+	void setRadius(qint32 radius);
+
+	[[nodiscard]] qint32 topLeftRadius() const;
+	void setTopLeftRadius(qint32 radius);
+	void resetTopLeftRadius();
+
+	[[nodiscard]] qint32 topRightRadius() const;
+	void setTopRightRadius(qint32 radius);
+	void resetTopRightRadius();
+
+	[[nodiscard]] qint32 bottomLeftRadius() const;
+	void setBottomLeftRadius(qint32 radius);
+	void resetBottomLeftRadius();
+
+	[[nodiscard]] qint32 bottomRightRadius() const;
+	void setBottomRightRadius(qint32 radius);
+	void resetBottomRightRadius();
+
 	QQmlListProperty<PendingRegion> regions();
 
 	[[nodiscard]] bool empty() const;
@@ -109,6 +151,11 @@ signals:
 	void yChanged();
 	void widthChanged();
 	void heightChanged();
+	void radiusChanged();
+	void topLeftRadiusChanged();
+	void topRightRadiusChanged();
+	void bottomLeftRadiusChanged();
+	void bottomRightRadiusChanged();
 	void childrenChanged();
 
 	/// Triggered when the region's geometry changes.
@@ -130,12 +177,25 @@ private:
 	static void
 	regionsReplace(QQmlListProperty<PendingRegion>* prop, qsizetype i, PendingRegion* region);
 
+	enum CornerOverride : quint8 {
+		TopLeft = 0b1,
+		TopRight = 0b10,
+		BottomLeft = 0b100,
+		BottomRight = 0b1000,
+	};
+
 	QQuickItem* mItem = nullptr;
 
 	qint32 mX = 0;
 	qint32 mY = 0;
 	qint32 mWidth = 0;
 	qint32 mHeight = 0;
+	qint32 mRadius = 0;
+	qint32 mTopLeftRadius = 0;
+	qint32 mTopRightRadius = 0;
+	qint32 mBottomLeftRadius = 0;
+	qint32 mBottomRightRadius = 0;
+	quint8 mCornerOverrides = 0;
 
 	QList<PendingRegion*> mRegions;
 };

src/crash/main.cpp

@@ -230,7 +230,9 @@ void qsCheckCrash(int argc, char** argv) {
 	);
 
 	auto app = QApplication(argc, argv);
-	QApplication::setDesktopFileName("org.quickshell");
+	auto desktopId =
+	    info.instance.appId.isEmpty() ? QStringLiteral("org.quickshell") : info.instance.appId;
+	QApplication::setDesktopFileName(desktopId);
 
 	auto crashDir = QsPaths::crashDir(info.instance.instanceId);
 

src/launch/launch.cpp

@@ -76,6 +76,7 @@ int launch(const LaunchArgs& args, char** argv, QCoreApplication* coreApplicatio
 		bool useSystemStyle = false;
 		QString iconTheme = qEnvironmentVariable("QS_ICON_THEME");
 		QHash<QString, QString> envOverrides;
+		QString appId = qEnvironmentVariable("QS_APP_ID");
 		QString dataDir;
 		QString stateDir;
 		QString cacheDir;
@@ -104,6 +105,8 @@ int launch(const LaunchArgs& args, char** argv, QCoreApplication* coreApplicatio
 				auto var = envPragma.sliced(0, splitIdx).trimmed();
 				auto val = envPragma.sliced(splitIdx + 1).trimmed();
 				pragmas.envOverrides.insert(var, val);
+			} else if (pragma.startsWith("AppId ")) {
+				pragmas.appId = pragma.sliced(6).trimmed();
 			} else if (pragma.startsWith("ShellId ")) {
 				shellId = pragma.sliced(8).trimmed();
 			} else if (pragma.startsWith("DataDir ")) {
@@ -128,10 +131,13 @@ int launch(const LaunchArgs& args, char** argv, QCoreApplication* coreApplicatio
 	qInfo() << "Shell ID:" << shellId << "Path ID" << pathId;
 
 	auto launchTime = qs::Common::LAUNCH_TIME.toSecsSinceEpoch();
+	auto appId = pragmas.appId.isEmpty() ? QStringLiteral("org.quickshell") : pragmas.appId;
+
 	InstanceInfo::CURRENT = InstanceInfo {
 	    .instanceId = base36Encode(getpid()) + base36Encode(launchTime),
 	    .configPath = args.configPath,
 	    .shellId = shellId,
+	    .appId = appId,
 	    .launchTime = qs::Common::LAUNCH_TIME,
 	    .pid = getpid(),
 	    .display = getDisplayConnection(),
@@ -231,7 +237,7 @@ int launch(const LaunchArgs& args, char** argv, QCoreApplication* coreApplicatio
 		app = new QGuiApplication(qArgC, argv);
 	}
 
-	QGuiApplication::setDesktopFileName("org.quickshell");
+	QGuiApplication::setDesktopFileName(appId);
 
 	if (args.debugPort != -1) {
 		QQmlDebuggingEnabler::enableDebugging(true);

src/wayland/CMakeLists.txt

@@ -68,6 +68,7 @@ function (wl_proto target name dir)
 	target_include_directories(${target} INTERFACE ${PROTO_BUILD_PATH})
 	target_link_libraries(${target} wl-proto-${name}-wl Qt6::WaylandClient Qt6::WaylandClientPrivate)
 	qs_pch(${target} SET wayland-protocol)
+	target_compile_options(wl-proto-${name}-wl PRIVATE ${wayland_CFLAGS})
 endfunction()
 
 # -----
@@ -119,6 +120,9 @@ if (HYPRLAND)
 	add_subdirectory(hyprland)
 endif()
 
+add_subdirectory(background_effect)
+list(APPEND WAYLAND_MODULES Quickshell.Wayland._BackgroundEffect)
+
 add_subdirectory(idle_inhibit)
 list(APPEND WAYLAND_MODULES Quickshell.Wayland._IdleInhibitor)
 

src/wayland/background_effect/CMakeLists.txt

@@ -0,0 +1,24 @@
+qt_add_library(quickshell-wayland-background-effect STATIC
+	manager.cpp
+	surface.cpp
+	qml.cpp
+)
+
+qt_add_qml_module(quickshell-wayland-background-effect
+	URI Quickshell.Wayland._BackgroundEffect
+	VERSION 0.1
+	DEPENDENCIES QtQml
+)
+
+install_qml_module(quickshell-wayland-background-effect)
+
+wl_proto(wlp-background-effect ext-background-effect-v1 "${WAYLAND_PROTOCOLS}/staging/ext-background-effect")
+
+target_link_libraries(quickshell-wayland-background-effect PRIVATE
+	Qt::Quick Qt::WaylandClient Qt::WaylandClientPrivate wayland-client
+	wlp-background-effect
+)
+
+qs_module_pch(quickshell-wayland-background-effect)
+
+target_link_libraries(quickshell PRIVATE quickshell-wayland-background-effectplugin)

src/wayland/background_effect/manager.cpp

@@ -0,0 +1,38 @@
+#include "manager.hpp"
+#include <cstdint>
+
+#include <private/qwaylandwindow_p.h>
+#include <qtmetamacros.h>
+#include <qwayland-ext-background-effect-v1.h>
+#include <qwaylandclientextension.h>
+
+#include "surface.hpp"
+
+namespace qs::wayland::background_effect::impl {
+
+BackgroundEffectManager::BackgroundEffectManager(): QWaylandClientExtensionTemplate(1) {
+	this->initialize();
+}
+
+BackgroundEffectSurface*
+BackgroundEffectManager::createEffectSurface(QtWaylandClient::QWaylandWindow* window) {
+	return new BackgroundEffectSurface(this->get_background_effect(window->surface()));
+}
+
+bool BackgroundEffectManager::blurAvailable() const {
+	return this->isActive() && this->mBlurAvailable;
+}
+
+void BackgroundEffectManager::ext_background_effect_manager_v1_capabilities(uint32_t flags) {
+	auto available = static_cast<bool>(flags & capability_blur);
+	if (available == this->mBlurAvailable) return;
+	this->mBlurAvailable = available;
+	emit this->blurAvailableChanged();
+}
+
+BackgroundEffectManager* BackgroundEffectManager::instance() {
+	static auto* instance = new BackgroundEffectManager(); // NOLINT
+	return instance->isInitialized() ? instance : nullptr;
+}
+
+} // namespace qs::wayland::background_effect::impl

src/wayland/background_effect/manager.hpp

@@ -0,0 +1,37 @@
+#pragma once
+
+#include <private/qwaylandwindow_p.h>
+#include <qobject.h>
+#include <qtmetamacros.h>
+#include <qwayland-ext-background-effect-v1.h>
+#include <qwaylandclientextension.h>
+
+#include "surface.hpp"
+
+namespace qs::wayland::background_effect::impl {
+
+class BackgroundEffectManager
+    : public QWaylandClientExtensionTemplate<BackgroundEffectManager>
+    , public QtWayland::ext_background_effect_manager_v1 {
+	Q_OBJECT;
+
+public:
+	explicit BackgroundEffectManager();
+
+	BackgroundEffectSurface* createEffectSurface(QtWaylandClient::QWaylandWindow* window);
+
+	[[nodiscard]] bool blurAvailable() const;
+
+	static BackgroundEffectManager* instance();
+
+signals:
+	void blurAvailableChanged();
+
+protected:
+	void ext_background_effect_manager_v1_capabilities(uint32_t flags) override;
+
+private:
+	bool mBlurAvailable = false;
+};
+
+} // namespace qs::wayland::background_effect::impl

src/wayland/background_effect/qml.cpp

@@ -0,0 +1,246 @@
+#include "qml.hpp"
+#include <memory>
+
+#include <private/qhighdpiscaling_p.h>
+#include <private/qwaylandwindow_p.h>
+#include <qcoreevent.h>
+#include <qevent.h>
+#include <qlogging.h>
+#include <qnumeric.h>
+#include <qobject.h>
+#include <qregion.h>
+#include <qtmetamacros.h>
+#include <qvariant.h>
+#include <qwindow.h>
+
+#include "../../core/region.hpp"
+#include "../../window/proxywindow.hpp"
+#include "../../window/windowinterface.hpp"
+#include "manager.hpp"
+#include "surface.hpp"
+
+using QtWaylandClient::QWaylandWindow;
+
+namespace qs::wayland::background_effect {
+
+BackgroundEffect* BackgroundEffect::qmlAttachedProperties(QObject* object) {
+	auto* proxyWindow = qobject_cast<ProxyWindowBase*>(object);
+
+	if (!proxyWindow) {
+		if (auto* iface = qobject_cast<WindowInterface*>(object)) {
+			proxyWindow = iface->proxyWindow();
+		}
+	}
+
+	if (!proxyWindow) return nullptr;
+	return new BackgroundEffect(proxyWindow);
+}
+
+BackgroundEffect::BackgroundEffect(ProxyWindowBase* window): QObject(nullptr), proxyWindow(window) {
+	QObject::connect(
+	    window,
+	    &ProxyWindowBase::windowConnected,
+	    this,
+	    &BackgroundEffect::onWindowConnected
+	);
+
+	QObject::connect(window, &ProxyWindowBase::polished, this, &BackgroundEffect::onWindowPolished);
+
+	QObject::connect(
+	    window,
+	    &ProxyWindowBase::devicePixelRatioChanged,
+	    this,
+	    &BackgroundEffect::updateBlurRegion
+	);
+
+	QObject::connect(window, &QObject::destroyed, this, &BackgroundEffect::onProxyWindowDestroyed);
+
+	if (window->backingWindow()) {
+		this->onWindowConnected();
+	}
+}
+
+PendingRegion* BackgroundEffect::blurRegion() const { return this->mBlurRegion; }
+
+void BackgroundEffect::setBlurRegion(PendingRegion* region) {
+	if (region == this->mBlurRegion) return;
+
+	if (this->mBlurRegion) {
+		QObject::disconnect(this->mBlurRegion, nullptr, this, nullptr);
+	}
+
+	this->mBlurRegion = region;
+
+	if (region) {
+		QObject::connect(region, &QObject::destroyed, this, &BackgroundEffect::onBlurRegionDestroyed);
+		QObject::connect(region, &PendingRegion::changed, this, &BackgroundEffect::updateBlurRegion);
+	}
+
+	this->updateBlurRegion();
+	emit this->blurRegionChanged();
+}
+
+void BackgroundEffect::onBlurRegionDestroyed() {
+	this->mBlurRegion = nullptr;
+	this->updateBlurRegion();
+	emit this->blurRegionChanged();
+}
+
+void BackgroundEffect::updateBlurRegion() {
+	if (!this->surface || !this->proxyWindow) return;
+
+	this->pendingBlurRegion = true;
+	this->proxyWindow->schedulePolish();
+}
+
+void BackgroundEffect::onWindowPolished() {
+	if (!this->surface || !this->pendingBlurRegion) return;
+	if (!this->mWaylandWindow || !this->mWaylandWindow->surface()) {
+		this->pendingBlurRegion = false;
+		return;
+	}
+
+	QRegion region;
+	if (this->mBlurRegion) {
+		region =
+		    this->mBlurRegion->applyTo(QRect(0, 0, this->mWindow->width(), this->mWindow->height()));
+
+		auto scale = QHighDpiScaling::factor(this->mWindow);
+		if (!qFuzzyCompare(scale, 1.0)) {
+			region = QHighDpi::scale(region, scale);
+		}
+
+		auto margins = this->mWaylandWindow->clientSideMargins();
+		region.translate(margins.left(), margins.top());
+	}
+
+	this->surface->setBlurRegion(region);
+	this->pendingBlurRegion = false;
+}
+
+bool BackgroundEffect::eventFilter(QObject* object, QEvent* event) {
+	if (event->type() == QEvent::PlatformSurface) {
+		auto* surfaceEvent = dynamic_cast<QPlatformSurfaceEvent*>(event);
+		if (surfaceEvent->surfaceEventType() == QPlatformSurfaceEvent::SurfaceAboutToBeDestroyed) {
+			this->surface = nullptr;
+			this->pendingBlurRegion = false;
+		}
+	}
+
+	return this->QObject::eventFilter(object, event);
+}
+
+void BackgroundEffect::onWindowConnected() {
+	this->mWindow = this->proxyWindow->backingWindow();
+	this->mWindow->installEventFilter(this);
+
+	QObject::connect(
+	    this->mWindow,
+	    &QWindow::visibleChanged,
+	    this,
+	    &BackgroundEffect::onWindowVisibleChanged
+	);
+
+	this->onWindowVisibleChanged();
+}
+
+void BackgroundEffect::onWindowVisibleChanged() {
+	if (this->mWindow->isVisible()) {
+		if (!this->mWindow->handle()) {
+			this->mWindow->create();
+		}
+	}
+
+	auto* window = dynamic_cast<QWaylandWindow*>(this->mWindow->handle());
+	if (window == this->mWaylandWindow) return;
+
+	if (this->mWaylandWindow) {
+		QObject::disconnect(this->mWaylandWindow, nullptr, this, nullptr);
+	}
+
+	this->mWaylandWindow = window;
+	if (!window) return;
+
+	QObject::connect(
+	    this->mWaylandWindow,
+	    &QObject::destroyed,
+	    this,
+	    &BackgroundEffect::onWaylandWindowDestroyed
+	);
+
+	QObject::connect(
+	    this->mWaylandWindow,
+	    &QWaylandWindow::surfaceCreated,
+	    this,
+	    &BackgroundEffect::onWaylandSurfaceCreated
+	);
+
+	QObject::connect(
+	    this->mWaylandWindow,
+	    &QWaylandWindow::surfaceDestroyed,
+	    this,
+	    &BackgroundEffect::onWaylandSurfaceDestroyed
+	);
+
+	if (this->mWaylandWindow->surface()) {
+		this->onWaylandSurfaceCreated();
+	}
+}
+
+void BackgroundEffect::onWaylandWindowDestroyed() { this->mWaylandWindow = nullptr; }
+
+void BackgroundEffect::onWaylandSurfaceCreated() {
+	auto* manager = impl::BackgroundEffectManager::instance();
+
+	if (!manager) {
+		qWarning() << "Cannot enable background effect as ext-background-effect-v1 is not supported "
+		              "by the current compositor.";
+		return;
+	}
+
+	// Steal protocol surface from previous BackgroundEffect to avoid duplicate-attachment on reload.
+	auto v = this->mWaylandWindow->property("qs_background_effect");
+	if (v.canConvert<BackgroundEffect*>()) {
+		auto* prev = v.value<BackgroundEffect*>();
+		if (prev != this && prev->surface) {
+			this->surface.swap(prev->surface);
+		}
+	}
+
+	if (!this->surface) {
+		this->surface = std::unique_ptr<impl::BackgroundEffectSurface>(
+		    manager->createEffectSurface(this->mWaylandWindow)
+		);
+	}
+
+	this->mWaylandWindow->setProperty("qs_background_effect", QVariant::fromValue(this));
+
+	this->pendingBlurRegion = this->mBlurRegion != nullptr;
+	if (this->pendingBlurRegion) {
+		this->proxyWindow->schedulePolish();
+	}
+}
+
+void BackgroundEffect::onWaylandSurfaceDestroyed() {
+	this->surface = nullptr;
+	this->pendingBlurRegion = false;
+
+	if (!this->proxyWindow) {
+		this->deleteLater();
+	}
+}
+
+void BackgroundEffect::onProxyWindowDestroyed() {
+	// Don't delete the BackgroundEffect, and therefore the impl::BackgroundEffectSurface
+	// until the wl_surface is destroyed. Deleting it when the proxy window is deleted would
+	// cause a frame without blur between the destruction of the ext_background_effect_surface_v1
+	// and wl_surface objects.
+
+	this->proxyWindow = nullptr;
+
+	if (this->surface == nullptr) {
+		this->deleteLater();
+	}
+}
+
+} // namespace qs::wayland::background_effect

src/wayland/background_effect/qml.hpp

@@ -0,0 +1,80 @@
+#pragma once
+
+#include <memory>
+
+#include <private/qwaylandwindow_p.h>
+#include <qcoreevent.h>
+#include <qobject.h>
+#include <qqmlintegration.h>
+#include <qtmetamacros.h>
+#include <qwindow.h>
+
+#include "../../core/region.hpp"
+#include "../../window/proxywindow.hpp"
+#include "surface.hpp"
+
+namespace qs::wayland::background_effect {
+
+///! Background blur effect for Wayland surfaces.
+/// Applies background blur behind a @@Quickshell.QsWindow or subclass,
+/// as an attached object, using the [ext-background-effect-v1] Wayland protocol.
+///
+/// > [!NOTE] Using a background effect requires the compositor support the
+/// > [ext-background-effect-v1] protocol.
+///
+/// [ext-background-effect-v1]: https://wayland.app/protocols/ext-background-effect-v1
+///
+/// #### Example
+/// ```qml
+/// @@Quickshell.PanelWindow {
+///   id: root
+///   color: "#80000000"
+///
+///   BackgroundEffect.blurRegion: Region { item: root.contentItem }
+/// }
+/// ```
+class BackgroundEffect: public QObject {
+	Q_OBJECT;
+	// clang-format off
+	/// Region to blur behind the surface. Set to null to remove blur.
+	Q_PROPERTY(PendingRegion* blurRegion READ blurRegion WRITE setBlurRegion NOTIFY blurRegionChanged);
+	// clang-format on
+	QML_ELEMENT;
+	QML_UNCREATABLE("BackgroundEffect can only be used as an attached object.");
+	QML_ATTACHED(BackgroundEffect);
+
+public:
+	explicit BackgroundEffect(ProxyWindowBase* window);
+
+	[[nodiscard]] PendingRegion* blurRegion() const;
+	void setBlurRegion(PendingRegion* region);
+
+	static BackgroundEffect* qmlAttachedProperties(QObject* object);
+
+	bool eventFilter(QObject* object, QEvent* event) override;
+
+signals:
+	void blurRegionChanged();
+
+private slots:
+	void onWindowConnected();
+	void onWindowVisibleChanged();
+	void onWaylandWindowDestroyed();
+	void onWaylandSurfaceCreated();
+	void onWaylandSurfaceDestroyed();
+	void onProxyWindowDestroyed();
+	void onBlurRegionDestroyed();
+	void onWindowPolished();
+	void updateBlurRegion();
+
+private:
+	ProxyWindowBase* proxyWindow = nullptr;
+	QWindow* mWindow = nullptr;
+	QtWaylandClient::QWaylandWindow* mWaylandWindow = nullptr;
+
+	bool pendingBlurRegion = false;
+	PendingRegion* mBlurRegion = nullptr;
+	std::unique_ptr<impl::BackgroundEffectSurface> surface;
+};
+
+} // namespace qs::wayland::background_effect

src/wayland/background_effect/surface.cpp

@@ -0,0 +1,37 @@
+#include "surface.hpp"
+
+#include <private/qwaylanddisplay_p.h>
+#include <private/qwaylandintegration_p.h>
+#include <qregion.h>
+#include <qwayland-ext-background-effect-v1.h>
+#include <wayland-client-protocol.h>
+
+namespace qs::wayland::background_effect::impl {
+
+BackgroundEffectSurface::BackgroundEffectSurface(
+    ::ext_background_effect_surface_v1* surface // NOLINT(misc-include-cleaner)
+)
+    : QtWayland::ext_background_effect_surface_v1(surface) {}
+
+BackgroundEffectSurface::~BackgroundEffectSurface() {
+	if (!this->isInitialized()) return;
+	this->destroy();
+}
+
+void BackgroundEffectSurface::setBlurRegion(const QRegion& region) {
+	if (!this->isInitialized()) return;
+
+	if (region.isEmpty()) {
+		this->set_blur_region(nullptr);
+		return;
+	}
+
+	static const auto* waylandIntegration = QtWaylandClient::QWaylandIntegration::instance();
+	auto* display = waylandIntegration->display();
+
+	auto* wlRegion = display->createRegion(region);
+	this->set_blur_region(wlRegion);
+	wl_region_destroy(wlRegion); // NOLINT(misc-include-cleaner)
+}
+
+} // namespace qs::wayland::background_effect::impl

src/wayland/background_effect/surface.hpp

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <qregion.h>
+#include <qtclasshelpermacros.h>
+#include <qwayland-ext-background-effect-v1.h>
+
+namespace qs::wayland::background_effect::impl {
+
+class BackgroundEffectSurface: public QtWayland::ext_background_effect_surface_v1 {
+public:
+	explicit BackgroundEffectSurface(::ext_background_effect_surface_v1* surface);
+	~BackgroundEffectSurface() override;
+	Q_DISABLE_COPY_MOVE(BackgroundEffectSurface);
+
+	void setBlurRegion(const QRegion& region);
+};
+
+} // namespace qs::wayland::background_effect::impl

src/wayland/background_effect/test/manual/background_effect.qml

@@ -0,0 +1,62 @@
+import QtQuick
+import QtQuick.Layouts
+import QtQuick.Controls
+import Quickshell
+import Quickshell.Wayland
+
+FloatingWindow {
+  id: root
+  color: "transparent"
+	contentItem.palette.windowText: "white"
+
+	ColumnLayout {
+		anchors.centerIn: parent
+
+		CheckBox {
+			id: enableBox
+			checked: true
+			text: "Enable Blur"
+		}
+
+		Button {
+			text: "Hide->Show"
+			onClicked: {
+				root.visible = false
+				showTimer.start()
+			}
+		}
+
+		Timer {
+			id: showTimer
+			interval: 200
+			onTriggered: root.visible = true
+		}
+
+		Slider {
+			id: radiusSlider
+			from: 0
+			to: 1000
+			value: 100
+		}
+
+		component EdgeSlider: Slider {
+			from: -1
+			to: 1000
+			value: -1
+		}
+
+		EdgeSlider { id: topLeftSlider }
+		EdgeSlider { id: topRightSlider }
+		EdgeSlider { id: bottomLeftSlider }
+		EdgeSlider { id: bottomRightSlider }
+	}
+
+	BackgroundEffect.blurRegion: Region {
+		item: enableBox.checked ? root.contentItem : null
+		radius: radiusSlider.value == -1 ? undefined : radiusSlider.value
+		topLeftRadius: topLeftSlider.value == -1 ? undefined : topLeftSlider.value
+		topRightRadius: topRightSlider.value == -1 ? undefined : topRightSlider.value
+		bottomLeftRadius: bottomLeftSlider.value == -1 ? undefined : bottomLeftSlider.value
+		bottomRightRadius: bottomRightSlider.value == -1 ? undefined : bottomRightSlider.value
+	}
+}

src/wayland/module.md

@@ -8,5 +8,6 @@ headers = [
 	"idle_inhibit/inhibitor.hpp",
 	"idle_notify/monitor.hpp",
 	"shortcuts_inhibit/inhibitor.hpp",
+	"background_effect/qml.hpp",
 ]
 -----