wayland: implement the alpha-modifier protocol

The alpha modifier protocol allows clients to set a multiplier for the opacity
of a surface, which allows them to offload some operations to KWin, which
in turn may offload them to KMS in the future

CMakeLists.txt

@@ -211,7 +211,7 @@ else()
     set(HAVE_WL_DISPLAY_SET_DEFAULT_MAX_BUFFER_SIZE 0)
 endif()
 
-find_package(WaylandProtocols 1.34)
+find_package(WaylandProtocols 1.36)
 set_package_properties(WaylandProtocols PROPERTIES
     TYPE REQUIRED
     PURPOSE "Collection of Wayland protocols that add functionality not available in the Wayland core protocol"

src/scene/surfaceitem_wayland.cpp

@@ -47,6 +47,7 @@ SurfaceItemWayland::SurfaceItemWayland(SurfaceInterface *surface, Item *parent)
     connect(surface, &SurfaceInterface::presentationModeHintChanged,
             this, &SurfaceItemWayland::handlePresentationModeHintChanged);
     connect(surface, &SurfaceInterface::bufferReleasePointChanged, this, &SurfaceItemWayland::handleReleasePointChanged);
+    connect(surface, &SurfaceInterface::alphaMultiplierChanged, this, &SurfaceItemWayland::handleAlphaMultiplierChanged);
 
     SubSurfaceInterface *subsurface = surface->subSurface();
     if (subsurface) {
@@ -66,6 +67,7 @@ SurfaceItemWayland::SurfaceItemWayland(SurfaceInterface *surface, Item *parent)
     setBufferSourceBox(surface->bufferSourceBox());
     setBufferSize(surface->bufferSize());
     setColorDescription(surface->colorDescription());
+    setOpacity(surface->alphaMultiplier());
 }
 
 QList<QRectF> SurfaceItemWayland::shape() const
@@ -216,6 +218,11 @@ void SurfaceItemWayland::handleReleasePointChanged()
     m_bufferReleasePoint = m_surface->bufferReleasePoint();
 }
 
+void SurfaceItemWayland::handleAlphaMultiplierChanged()
+{
+    setOpacity(m_surface->alphaMultiplier());
+}
+
 SurfacePixmapWayland::SurfacePixmapWayland(SurfaceItemWayland *item, QObject *parent)
     : SurfacePixmap(Compositor::self()->backend()->createSurfaceTextureWayland(this), parent)
     , m_item(item)

src/scene/surfaceitem_wayland.h

@@ -50,6 +50,7 @@ private Q_SLOTS:
     void handleColorDescriptionChanged();
     void handlePresentationModeHintChanged();
     void handleReleasePointChanged();
+    void handleAlphaMultiplierChanged();
 
 protected:
     std::unique_ptr<SurfacePixmap> createPixmap() override;

src/wayland/CMakeLists.txt

@@ -315,10 +315,15 @@ ecm_add_qtwayland_server_protocol_kde(WaylandProtocols_xml
     PROTOCOL ${PLASMA_WAYLAND_PROTOCOLS_DIR}/kde-external-brightness-v1.xml
     BASENAME kde-external-brightness-v1
 )
+ecm_add_qtwayland_server_protocol_kde(WaylandProtocols_xml
+    PROTOCOL ${WaylandProtocols_DATADIR}/staging/alpha-modifier/alpha-modifier-v1.xml
+    BASENAME alpha-modifier-v1
+)
 
 target_sources(kwin PRIVATE
     abstract_data_source.cpp
     abstract_drop_handler.cpp
+    alphamodifier_v1.cpp
     appmenu.cpp
     blur.cpp
     clientconnection.cpp
@@ -403,6 +408,7 @@ target_sources(kwin PRIVATE
 )
 
 install(FILES
+    alphamodifier_v1.h
     appmenu.h
     blur.h
     clientconnection.h
@@ -478,12 +484,14 @@ install(FILES
     xwaylandshell_v1.h
     xx_colormanagement_v4.h
 
+    ${CMAKE_CURRENT_BINARY_DIR}/qwayland-server-alpha-modifier-v1.h
     ${CMAKE_CURRENT_BINARY_DIR}/qwayland-server-content-type-v1.h
     ${CMAKE_CURRENT_BINARY_DIR}/qwayland-server-frog-color-management-v1.h
     ${CMAKE_CURRENT_BINARY_DIR}/qwayland-server-kde-external-brightness-v1.h
     ${CMAKE_CURRENT_BINARY_DIR}/qwayland-server-linux-drm-syncobj-v1.h
     ${CMAKE_CURRENT_BINARY_DIR}/qwayland-server-presentation-time.h
     ${CMAKE_CURRENT_BINARY_DIR}/qwayland-server-xx-color-management-v4.h
+    ${CMAKE_CURRENT_BINARY_DIR}/wayland-alpha-modifier-v1-server-protocol.h
     ${CMAKE_CURRENT_BINARY_DIR}/wayland-content-type-v1-server-protocol.h
     ${CMAKE_CURRENT_BINARY_DIR}/wayland-frog-color-management-v1-server-protocol.h
     ${CMAKE_CURRENT_BINARY_DIR}/wayland-kde-external-brightness-v1-server-protocol.h

src/wayland/alphamodifier_v1.cpp

@@ -0,0 +1,75 @@
+/*
+    SPDX-FileCopyrightText: 2024 Xaver Hugl <xaver.hugl@gmail.com>
+
+    SPDX-License-Identifier: LGPL-2.1-only OR LGPL-3.0-only OR LicenseRef-KDE-Accepted-LGPL
+*/
+#include "alphamodifier_v1.h"
+
+#include "display.h"
+#include "surface.h"
+#include "surface_p.h"
+
+namespace KWin
+{
+
+static constexpr uint32_t s_version = 1;
+
+AlphaModifierManagerV1::AlphaModifierManagerV1(Display *display, QObject *parent)
+    : QObject(parent)
+    , QtWaylandServer::wp_alpha_modifier_v1(*display, s_version)
+{
+}
+
+void AlphaModifierManagerV1::wp_alpha_modifier_v1_destroy(Resource *resource)
+{
+    wl_resource_destroy(resource->handle);
+}
+
+void AlphaModifierManagerV1::wp_alpha_modifier_v1_get_surface(Resource *resource, uint32_t id, ::wl_resource *surface)
+{
+    SurfaceInterface *surf = SurfaceInterface::get(surface);
+    SurfaceInterfacePrivate *priv = SurfaceInterfacePrivate::get(surf);
+    if (priv->alphaModifier) {
+        wl_resource_post_error(surface, error_already_constructed, "wl_surface already has an alpha modifier surface");
+        return;
+    }
+    new AlphaModifierSurfaceV1(resource->client(), id, resource->version(), surf);
+}
+
+AlphaModifierSurfaceV1::AlphaModifierSurfaceV1(wl_client *client, uint32_t id, uint32_t version, SurfaceInterface *surface)
+    : QtWaylandServer::wp_alpha_modifier_surface_v1(client, id, version)
+    , m_surface(surface)
+{
+}
+
+AlphaModifierSurfaceV1::~AlphaModifierSurfaceV1()
+{
+    if (m_surface) {
+        const auto priv = SurfaceInterfacePrivate::get(m_surface);
+        priv->pending->alphaMultiplier = 1;
+        priv->pending->alphaMultiplierIsSet = true;
+    }
+}
+
+void AlphaModifierSurfaceV1::wp_alpha_modifier_surface_v1_destroy_resource(Resource *resource)
+{
+    delete this;
+}
+
+void AlphaModifierSurfaceV1::wp_alpha_modifier_surface_v1_destroy(Resource *resource)
+{
+    wl_resource_destroy(resource->handle);
+}
+
+void AlphaModifierSurfaceV1::wp_alpha_modifier_surface_v1_set_multiplier(Resource *resource, uint32_t factor)
+{
+    if (!m_surface) {
+        wl_resource_post_error(resource->handle, error_no_surface, "wl_surface was destroyed before a set_multiplier request");
+        return;
+    }
+    const auto priv = SurfaceInterfacePrivate::get(m_surface);
+    priv->pending->alphaMultiplier = factor / double(std::numeric_limits<uint32_t>::max());
+    priv->pending->alphaMultiplierIsSet = true;
+}
+
+}

src/wayland/alphamodifier_v1.h

@@ -0,0 +1,44 @@
+/*
+    SPDX-FileCopyrightText: 2024 Xaver Hugl <xaver.hugl@gmail.com>
+
+    SPDX-License-Identifier: LGPL-2.1-only OR LGPL-3.0-only OR LicenseRef-KDE-Accepted-LGPL
+*/
+#pragma once
+
+#include "kwin_export.h"
+#include "wayland/qwayland-server-alpha-modifier-v1.h"
+
+#include <QObject>
+#include <QPointer>
+
+namespace KWin
+{
+
+class Display;
+class SurfaceInterface;
+
+class KWIN_EXPORT AlphaModifierManagerV1 : public QObject, private QtWaylandServer::wp_alpha_modifier_v1
+{
+public:
+    explicit AlphaModifierManagerV1(Display *display, QObject *parent);
+
+private:
+    void wp_alpha_modifier_v1_destroy(Resource *resource) override;
+    void wp_alpha_modifier_v1_get_surface(Resource *resource, uint32_t id, ::wl_resource *surface) override;
+};
+
+class AlphaModifierSurfaceV1 : private QtWaylandServer::wp_alpha_modifier_surface_v1
+{
+public:
+    explicit AlphaModifierSurfaceV1(wl_client *client, uint32_t id, uint32_t version, SurfaceInterface *surface);
+    ~AlphaModifierSurfaceV1() override;
+
+private:
+    void wp_alpha_modifier_surface_v1_destroy_resource(Resource *resource) override;
+    void wp_alpha_modifier_surface_v1_destroy(Resource *resource) override;
+    void wp_alpha_modifier_surface_v1_set_multiplier(Resource *resource, uint32_t factor) override;
+
+    const QPointer<SurfaceInterface> m_surface;
+};
+
+}

src/wayland/surface.cpp

@@ -589,6 +589,10 @@ void SurfaceState::mergeInto(SurfaceState *target)
         target->colorDescription = colorDescription;
         target->colorDescriptionIsSet = true;
     }
+    if (alphaMultiplierIsSet) {
+        target->alphaMultiplier = alphaMultiplier;
+        target->alphaMultiplierIsSet = true;
+    }
     target->presentationFeedback = std::move(presentationFeedback);
 
     *this = SurfaceState{};
@@ -611,6 +615,7 @@ void SurfaceInterfacePrivate::applyState(SurfaceState *next)
     const bool colorDescriptionChanged = next->colorDescriptionIsSet;
     const bool presentationModeHintChanged = next->presentationModeHintIsSet;
     const bool bufferReleasePointChanged = next->bufferIsSet && current->releasePoint != next->releasePoint;
+    const bool alphaMultiplierChanged = next->alphaMultiplierIsSet;
 
     const QSizeF oldSurfaceSize = surfaceSize;
     const QSize oldBufferSize = bufferSize;
@@ -706,6 +711,9 @@ void SurfaceInterfacePrivate::applyState(SurfaceState *next)
     if (bufferReleasePointChanged) {
         Q_EMIT q->bufferReleasePointChanged();
     }
+    if (alphaMultiplierChanged) {
+        Q_EMIT q->alphaMultiplierChanged();
+    }
 
     if (bufferChanged) {
         if (current->buffer && (!current->damage.isEmpty() || !current->bufferDamage.isEmpty())) {
@@ -1210,6 +1218,11 @@ std::shared_ptr<SyncReleasePoint> SurfaceInterface::bufferReleasePoint() const
     return d->current->releasePoint;
 }
 
+double SurfaceInterface::alphaMultiplier() const
+{
+    return d->current->alphaMultiplier;
+}
+
 } // namespace KWin
 
 #include "moc_surface.cpp"

src/wayland/surface.h

@@ -344,6 +344,8 @@ public:
 
     void setPreferredColorDescription(const ColorDescription &descr);
 
+    double alphaMultiplier() const;
+
     /**
      * Returns the current release point for the buffer on this surface. The buffer keeps the
      * release point referenced as long as it's referenced itself; for synchronization on the
@@ -437,6 +439,7 @@ Q_SIGNALS:
     void colorDescriptionChanged();
     void presentationModeHintChanged();
     void bufferReleasePointChanged();
+    void alphaMultiplierChanged();
 
     /**
      * Emitted when the Surface has been committed.

src/wayland/surface_p.h

@@ -30,6 +30,7 @@ class PresentationTimeFeedback;
 class XXColorSurfaceV4;
 class XXColorFeedbackSurfaceV4;
 class LinuxDrmSyncObjSurfaceV1;
+class AlphaModifierSurfaceV1;
 
 struct SurfaceState
 {
@@ -60,6 +61,7 @@ struct SurfaceState
     bool contentTypeIsSet = false;
     bool presentationModeHintIsSet = false;
     bool colorDescriptionIsSet = false;
+    bool alphaMultiplierIsSet = false;
     qint32 bufferScale = 1;
     OutputTransform bufferTransform = OutputTransform::Normal;
     wl_list frameCallbacks;
@@ -80,6 +82,7 @@ struct SurfaceState
         uint64_t point = 0;
     } acquirePoint;
     std::shared_ptr<SyncReleasePoint> releasePoint;
+    double alphaMultiplier = 1;
 
     struct
     {
@@ -181,6 +184,7 @@ public:
     XXColorSurfaceV4 *xxColorSurface = nullptr;
     QList<XXColorFeedbackSurfaceV4 *> xxColorFeedbacks;
     LinuxDrmSyncObjSurfaceV1 *syncObjV1 = nullptr;
+    AlphaModifierSurfaceV1 *alphaModifier = nullptr;
 
     struct
     {

src/wayland_server.cpp

@@ -23,6 +23,7 @@
 #include "utils/kernel.h"
 #include "utils/serviceutils.h"
 #include "virtualdesktops.h"
+#include "wayland/alphamodifier_v1.h"
 #include "wayland/appmenu.h"
 #include "wayland/clientconnection.h"
 #include "wayland/compositor.h"
@@ -525,7 +526,7 @@ bool WaylandServer::init()
     });
 
     m_externalBrightness = new ExternalBrightnessV1(m_display, m_display);
-
+    m_alphaModifierManager = new AlphaModifierManagerV1(m_display, m_display);
     return true;
 }
 

src/wayland_server.h

@@ -63,6 +63,7 @@ class PresentationTime;
 class XXColorManagerV4;
 class LinuxDrmSyncObjV1Interface;
 class RenderBackend;
+class AlphaModifierManagerV1;
 
 class KWIN_EXPORT WaylandServer : public QObject
 {
@@ -291,6 +292,7 @@ private:
     XXColorManagerV4 *m_xxColorManager = nullptr;
     XdgDialogWmV1Interface *m_xdgDialogWm = nullptr;
     ExternalBrightnessV1 *m_externalBrightness = nullptr;
+    AlphaModifierManagerV1 *m_alphaModifierManager = nullptr;
     KWIN_SINGLETON(WaylandServer)
 };