RFC: Allow specifying margins in percents

Absolute margin values pose a problem if you want to place a surface
certain distance away from a screen edge (in percents) but you also want
the compositor to place the surface on the active output.

At the moment, this issue is worked around by using kwin dbus api to
query the active output. This is not good.

This change is a take on allowing to specify margin values in percents.
It can be used to drop a dbus call in krunner and assist us with porting
other components to layer shell, e.g. OSDs, they also need to be placed
one third away the bottom screen edge.

src/interfaces/window.cpp

@@ -17,6 +17,49 @@
 
 using namespace LayerShellQt;
 
+Margin::Margin()
+    : m_value(0)
+{
+}
+
+Margin::Margin(int pixels)
+    : m_value(pixels)
+{
+}
+
+Margin::Margin(qreal percents)
+    : m_value(percents)
+{
+}
+
+Margin Margin::fromPixels(int pixels)
+{
+    return Margin(pixels);
+}
+
+Margin Margin::fromPercents(qreal percents)
+{
+    return Margin(percents);
+}
+
+std::optional<int> Margin::pixels() const
+{
+    if (std::holds_alternative<int>(m_value)) {
+        return std::get<int>(m_value);
+    } else {
+        return std::nullopt;
+    }
+}
+
+std::optional<qreal> Margin::percents() const
+{
+    if (std::holds_alternative<qreal>(m_value)) {
+        return std::get<qreal>(m_value);
+    } else {
+        return std::nullopt;
+    }
+}
+
 class LayerShellQt::WindowPrivate
 {
 public:
@@ -32,10 +75,12 @@ public:
     Window::Anchor exclusiveEdge = Window::AnchorNone;
     Window::KeyboardInteractivity keyboardInteractivity = Window::KeyboardInteractivityOnDemand;
     Window::Layer layer = Window::LayerTop;
-    QMargins margins;
+    Margin leftMargin;
+    Margin topMargin;
+    Margin rightMargin;
+    Margin bottomMargin;
     QSize desiredSize = QSize(0, 0);
-    QPointer<QScreen> desiredScreen;
-    bool desiredActiveScreen = false;
+    Window::ScreenConfiguration screenConfiguration = Window::ScreenFromQWindow;
     bool closeOnDismissed = true;
     bool activateOnShow = true;
 };
@@ -90,15 +135,74 @@ Window::Anchor Window::exclusiveEdge() const
 
 void Window::setMargins(const QMargins &margins)
 {
-    if (d->margins != margins) {
-        d->margins = margins;
-        Q_EMIT marginsChanged();
-    }
+    setLeftMargin(Margin::fromPixels(margins.left()));
+    setTopMargin(Margin::fromPixels(margins.top()));
+    setRightMargin(Margin::fromPixels(margins.right()));
+    setBottomMargin(Margin::fromPixels(margins.bottom()));
 }
 
 QMargins Window::margins() const
 {
-    return d->margins;
+    return QMargins(d->leftMargin.pixels().value_or(0),
+                    d->topMargin.pixels().value_or(0),
+                    d->rightMargin.pixels().value_or(0),
+                    d->bottomMargin.pixels().value_or(0));
+}
+
+void Window::setLeftMargin(Margin margin)
+{
+    if (d->leftMargin != margin) {
+        d->leftMargin = margin;
+        Q_EMIT leftMarginChanged();
+        Q_EMIT marginsChanged();
+    }
+}
+
+Margin Window::leftMargin() const
+{
+    return d->leftMargin;
+}
+
+void Window::setTopMargin(Margin margin)
+{
+    if (d->topMargin != margin) {
+        d->topMargin = margin;
+        Q_EMIT topMarginChanged();
+        Q_EMIT marginsChanged();
+    }
+}
+
+Margin Window::topMargin() const
+{
+    return d->topMargin;
+}
+
+void Window::setRightMargin(Margin margin)
+{
+    if (d->rightMargin != margin) {
+        d->rightMargin = margin;
+        Q_EMIT rightMarginChanged();
+        Q_EMIT marginsChanged();
+    }
+}
+
+Margin Window::rightMargin() const
+{
+    return d->rightMargin;
+}
+
+void Window::setBottomMargin(Margin margin)
+{
+    if (d->bottomMargin != margin) {
+        d->bottomMargin = margin;
+        Q_EMIT bottomMarginChanged();
+        Q_EMIT marginsChanged();
+    }
+}
+
+Margin Window::bottomMargin() const
+{
+    return d->bottomMargin;
 }
 
 void Window::setDesiredSize(const QSize &size)
@@ -153,46 +257,14 @@ Window::Layer Window::layer() const
     return d->layer;
 }
 
-void Window::setDesiredActiveScreen(bool set)
+Window::ScreenConfiguration Window::screenConfiguration() const
 {
-    if (d->desiredActiveScreen == set) {
-        return;
-    }
-
-    d->desiredActiveScreen = set;
-
-    if (d->desiredActiveScreen && d->desiredScreen) {
-        d->desiredScreen = nullptr;
-        Q_EMIT desiredScreenChanged();
-    }
-
-    Q_EMIT desiredActiveScreenChanged();
+    return d->screenConfiguration;
 }
 
-bool Window::desiredActiveScreen() const
+void Window::setScreenConfiguration(Window::ScreenConfiguration screenConfiguration)
 {
-    return d->desiredActiveScreen;
-}
-
-void Window::setDesiredScreen(QScreen *screen)
-{
-    if (d->desiredScreen == screen) {
-        return;
-    }
-
-    d->desiredScreen = screen;
-
-    if (d->desiredScreen && d->desiredActiveScreen) {
-        d->desiredActiveScreen = false;
-        Q_EMIT desiredActiveScreenChanged();
-    }
-
-    Q_EMIT desiredScreenChanged();
-}
-
-QScreen *Window::desiredScreen() const
-{
-    return d->desiredScreen;
+    d->screenConfiguration = screenConfiguration;
 }
 
 bool Window::closeOnDismissed() const

src/interfaces/window.h

@@ -18,6 +18,34 @@ namespace LayerShellQt
 {
 class WindowPrivate;
 
+/**
+ * The Margin type provides a way to specify how far a layer surface should be away from a screen edge.
+ *
+ * A margin can have an absolute value or a percent value. An absolute value indicates the distance
+ * in pixels. A percent value indicates the distance as a percentage of the output size, for example
+ * this can be used to tell the compositor that the surface should be one third of the output height from
+ * a screen edge, etc.
+ */
+class LAYERSHELLQT_EXPORT Margin
+{
+public:
+    static Margin fromPixels(int pixels);
+    static Margin fromPercents(qreal percents);
+
+    Margin();
+
+    std::optional<int> pixels() const;
+    std::optional<qreal> percents() const;
+
+    auto operator<=>(const Margin &other) const = default;
+
+private:
+    Margin(int pixels);
+    Margin(qreal percents);
+
+    std::variant<int, qreal> m_value;
+};
+
 class LAYERSHELLQT_EXPORT Window : public QObject
 {
     Q_OBJECT
@@ -27,9 +55,8 @@ class LAYERSHELLQT_EXPORT Window : public QObject
     Q_PROPERTY(qint32 exclusionZone READ exclusionZone WRITE setExclusiveZone NOTIFY exclusionZoneChanged)
     Q_PROPERTY(Layer layer READ layer WRITE setLayer NOTIFY layerChanged)
     Q_PROPERTY(KeyboardInteractivity keyboardInteractivity READ keyboardInteractivity WRITE setKeyboardInteractivity NOTIFY keyboardInteractivityChanged)
+    Q_PROPERTY(ScreenConfiguration screenConfiguration READ screenConfiguration WRITE setScreenConfiguration)
     Q_PROPERTY(bool activateOnShow READ activateOnShow WRITE setActivateOnShow)
-    Q_PROPERTY(bool desiredActiveScreen READ desiredActiveScreen WRITE setDesiredActiveScreen NOTIFY desiredActiveScreenChanged)
-    Q_PROPERTY(QScreen *desiredScreen READ desiredScreen WRITE setDesiredScreen NOTIFY desiredScreenChanged)
 
 public:
     ~Window() override;
@@ -65,6 +92,17 @@ public:
     };
     Q_ENUM(KeyboardInteractivity)
 
+    /**
+     * This enum type is used to specify which screen to place the surface on.
+     * ScreenFromQWindow (the default) reads QWindow::screen() while ScreenFromCompositor
+     * passes nil and lets the compositor decide.
+     */
+    enum ScreenConfiguration {
+        ScreenFromQWindow = 0,
+        ScreenFromCompositor = 1,
+    };
+    Q_ENUM(ScreenConfiguration)
+
     void setAnchors(Anchors anchor);
     Anchors anchors() const;
 
@@ -77,6 +115,18 @@ public:
     void setMargins(const QMargins &margins);
     QMargins margins() const;
 
+    void setLeftMargin(Margin margin);
+    Margin leftMargin() const;
+
+    void setTopMargin(Margin margin);
+    Margin topMargin() const;
+
+    void setRightMargin(Margin margin);
+    Margin rightMargin() const;
+
+    void setBottomMargin(Margin margin);
+    Margin bottomMargin() const;
+
     void setDesiredSize(const QSize &size);
     QSize desiredSize() const;
 
@@ -86,33 +136,8 @@ public:
     void setLayer(Layer layer);
     Layer layer() const;
 
-    /**
-     * Indicates whether the layer shell surface should be placed on the active screen based on @a set.
-     *
-     * The active screen depends on the compositor policies.
-     *
-     * If no explicit desired screen has been specified with the setDesiredScreen() function or the layer
-     * surface doesn't need to be placed on the active screen, i.e. setDesiredActiveScreen() has not
-     * been called, the QWindow::screen() will be used to decide what screen the layer shell surface
-     * should be placed on.
-     *
-     * The desiredScreen() will be reset if @a set is @c true.
-     */
-    void setDesiredActiveScreen(bool set);
-    bool desiredActiveScreen() const;
-
-    /**
-     * Indicates that the layer shell surface should be placed on the specified @a screen.
-     *
-     * If no explicit desired screen has been specified with the setDesiredScreen() function or the layer
-     * surface doesn't need to be placed on the active screen, i.e. setDesiredActiveScreen() has not
-     * been called, the QWindow::screen() will be used to decide what screen the layer shell surface
-     * should be placed on.
-     *
-     * The desiredActiveScreen() will be reset to @c false after calling this function.
-     */
-    void setDesiredScreen(QScreen *screen);
-    QScreen *desiredScreen() const;
+    void setScreenConfiguration(ScreenConfiguration screenConfiguration);
+    ScreenConfiguration screenConfiguration() const;
 
     /**
      * Sets a string based identifier for this window.
@@ -160,11 +185,13 @@ Q_SIGNALS:
     void exclusionZoneChanged();
     void exclusiveEdgeChanged();
     void marginsChanged();
+    void leftMarginChanged();
+    void topMarginChanged();
+    void rightMarginChanged();
+    void bottomMarginChanged();
     void desiredSizeChanged();
     void keyboardInteractivityChanged();
     void layerChanged();
-    void desiredActiveScreenChanged();
-    void desiredScreenChanged();
 
 private:
     void initializeShell();

src/qwaylandlayersurface.cpp

@@ -26,12 +26,7 @@ QWaylandLayerSurface::QWaylandLayerSurface(QWaylandLayerShellIntegration *shell,
     , m_window(window)
 {
     wl_output *output = nullptr;
-    if (!m_interface->desiredActiveScreen()) {
-        QScreen *desiredScreen = m_interface->desiredScreen();
-        if (!desiredScreen) {
-            window->window()->screen();
-        }
-
+    if (m_interface->screenConfiguration() == Window::ScreenFromQWindow) {
         auto waylandScreen = dynamic_cast<QtWaylandClient::QWaylandScreen *>(window->window()->screen()->handle());
         // Qt will always assign a screen to a window, but if the compositor has no screens available a dummy QScreen object is created
         // this will not cast to a QWaylandScreen
@@ -65,9 +60,24 @@ QWaylandLayerSurface::QWaylandLayerSurface(QWaylandLayerShellIntegration *shell,
         setExclusiveEdge(m_interface->exclusiveEdge());
     });
 
-    setMargins(m_interface->margins());
-    connect(m_interface, &Window::marginsChanged, this, [this]() {
-        setMargins(m_interface->margins());
+    setLeftMargin(m_interface->leftMargin());
+    connect(m_interface, &Window::leftMarginChanged, this, [this]() {
+        setLeftMargin(m_interface->leftMargin());
+    });
+
+    setTopMargin(m_interface->topMargin());
+    connect(m_interface, &Window::topMarginChanged, this, [this]() {
+        setTopMargin(m_interface->topMargin());
+    });
+
+    setRightMargin(m_interface->rightMargin());
+    connect(m_interface, &Window::rightMarginChanged, this, [this]() {
+        setRightMargin(m_interface->rightMargin());
+    });
+
+    setBottomMargin(m_interface->bottomMargin());
+    connect(m_interface, &Window::bottomMarginChanged, this, [this]() {
+        setBottomMargin(m_interface->bottomMargin());
     });
 
     connect(m_interface, &Window::desiredSizeChanged, this, [this]() {
@@ -164,9 +174,68 @@ void QWaylandLayerSurface::setExclusiveEdge(uint32_t edge)
     }
 }
 
-void QWaylandLayerSurface::setMargins(const QMargins &margins)
+void QWaylandLayerSurface::setLeftMargin(const Margin &margin)
 {
-    set_margin(margins.top(), margins.right(), margins.bottom(), margins.left());
+    if (zwlr_layer_surface_v1_get_version(object()) >= 6) {
+        if (const auto pixels = margin.pixels()) {
+            set_left_margin_absolute(*pixels);
+        } else if (const auto percents = margin.percents()) {
+            set_left_margin_percents(wl_fixed_from_double(*percents));
+        } else {
+            qCWarning(LAYERSHELLQT) << "Unspecified left margin for" << m_window->window();
+        }
+    } else {
+        const QMargins margins = m_interface->margins();
+        set_margin(margins.top(), margins.right(), margins.bottom(), margins.left());
+    }
+}
+
+void QWaylandLayerSurface::setTopMargin(const Margin &margin)
+{
+    if (zwlr_layer_surface_v1_get_version(object()) >= 6) {
+        if (const auto pixels = margin.pixels()) {
+            set_top_margin_absolute(*pixels);
+        } else if (const auto percents = margin.percents()) {
+            set_top_margin_percents(wl_fixed_from_double(*percents));
+        } else {
+            qCWarning(LAYERSHELLQT) << "Unspecified top margin for" << m_window->window();
+        }
+    } else {
+        const QMargins margins = m_interface->margins();
+        set_margin(margins.top(), margins.right(), margins.bottom(), margins.left());
+    }
+}
+
+void QWaylandLayerSurface::setRightMargin(const Margin &margin)
+{
+    if (zwlr_layer_surface_v1_get_version(object()) >= 6) {
+        if (const auto pixels = margin.pixels()) {
+            set_right_margin_absolute(*pixels);
+        } else if (const auto percents = margin.percents()) {
+            set_right_margin_percents(wl_fixed_from_double(*percents));
+        } else {
+            qCWarning(LAYERSHELLQT) << "Unspecified right margin for" << m_window->window();
+        }
+    } else {
+        const QMargins margins = m_interface->margins();
+        set_margin(margins.top(), margins.right(), margins.bottom(), margins.left());
+    }
+}
+
+void QWaylandLayerSurface::setBottomMargin(const Margin &margin)
+{
+    if (zwlr_layer_surface_v1_get_version(object()) >= 6) {
+        if (const auto pixels = margin.pixels()) {
+            set_bottom_margin_absolute(*pixels);
+        } else if (const auto percents = margin.percents()) {
+            set_bottom_margin_percents(wl_fixed_from_double(*percents));
+        } else {
+            qCWarning(LAYERSHELLQT) << "Unspecified bottom margin for" << m_window->window();
+        }
+    } else {
+        const QMargins margins = m_interface->margins();
+        set_margin(margins.top(), margins.right(), margins.bottom(), margins.left());
+    }
 }
 
 void QWaylandLayerSurface::setKeyboardInteractivity(uint32_t interactivity)

src/qwaylandlayersurface_p.h

@@ -19,6 +19,7 @@
 namespace LayerShellQt
 {
 
+class Margin;
 class Window;
 
 class LAYERSHELLQT_EXPORT QWaylandLayerSurface : public QtWaylandClient::QWaylandShellSurface, public QtWayland::zwlr_layer_surface_v1
@@ -38,7 +39,10 @@ public:
     void setAnchor(uint32_t anchor);
     void setExclusiveZone(int32_t zone);
     void setExclusiveEdge(uint32_t edge);
-    void setMargins(const QMargins &margins);
+    void setLeftMargin(const Margin &margin);
+    void setTopMargin(const Margin &margin);
+    void setRightMargin(const Margin &margin);
+    void setBottomMargin(const Margin &margin);
     void setKeyboardInteractivity(uint32_t interactivity);
     void setLayer(uint32_t layer);
 

src/wlr-layer-shell-unstable-v1.xml

@@ -25,7 +25,7 @@
     THIS SOFTWARE.
   </copyright>
 
-  <interface name="zwlr_layer_shell_v1" version="5">
+  <interface name="zwlr_layer_shell_v1" version="6">
     <description summary="create surfaces that are layers of the desktop">
       Clients can use this interface to assign the surface_layer role to
       wl_surfaces. Such surfaces are assigned to a "layer" of the output and
@@ -100,7 +100,7 @@
     </request>
   </interface>
 
-  <interface name="zwlr_layer_surface_v1" version="5">
+  <interface name="zwlr_layer_surface_v1" version="6">
     <description summary="layer metadata interface">
       An interface that may be implemented by a wl_surface, for surfaces that
       are designed to be rendered as a layer of a stacked desktop-like
@@ -403,5 +403,83 @@
       </description>
       <arg name="edge" type="uint"/>
     </request>
+
+    <!-- Version 6 additions -->
+
+    <request name="set_left_margin_absolute" since="6">
+      <description summary="set left margin in absolute pixels">
+        Sets the left margin in absolute pixels.
+
+        The left margin specified in percents will be overwritten.
+      </description>
+      <arg name="margin" type="int"/>
+    </request>
+
+    <request name="set_left_margin_percents" since="6">
+      <description summary="set the left margin proportional to area width">
+        Sets the left margin as a percentage of the area width. The
+        margin value is a number between 0 and 1.
+
+        The left margin specified in absolute values will be overwritten.
+      </description>
+      <arg name="margin" type="fixed"/>
+    </request>
+
+    <request name="set_top_margin_absolute" since="6">
+      <description summary="set top margin in absolute pixels">
+        Sets the top margin in absolute pixels.
+
+        The top margin specified in percents will be overwritten.
+      </description>
+      <arg name="margin" type="int"/>
+    </request>
+
+    <request name="set_top_margin_percents" since="6">
+      <description summary="set the top margin proportional to area width">
+        Sets the top margin as a percentage of the area width. The
+        margin value is a number between 0 and 1.
+
+        The top margin specified in absolute values will be overwritten.
+      </description>
+      <arg name="margin" type="fixed"/>
+    </request>
+
+    <request name="set_right_margin_absolute" since="6">
+      <description summary="set right margin in absolute pixels">
+        Sets the right margin in absolute pixels.
+
+        The right margin specified in percents will be overwritten.
+      </description>
+      <arg name="margin" type="int"/>
+    </request>
+
+    <request name="set_right_margin_percents" since="6">
+      <description summary="set the right margin proportional to area width">
+        Sets the right margin as a percentage of the area width. The
+        margin value is a number between 0 and 1.
+
+        The right margin specified in absolute values will be overwritten.
+      </description>
+      <arg name="margin" type="fixed"/>
+    </request>
+
+    <request name="set_bottom_margin_absolute" since="6">
+      <description summary="set bottom margin in absolute pixels">
+        Sets the bottom margin in absolute pixels.
+
+        The bottom margin specified in percents will be overwritten.
+      </description>
+      <arg name="margin" type="int"/>
+    </request>
+
+    <request name="set_bottom_margin_percents" since="6">
+      <description summary="set the bottom margin proportional to area width">
+        Sets the bottom margin as a percentage of the area width. The
+        margin value is a number between 0 and 1.
+
+        The bottom margin specified in absolute values will be overwritten.
+      </description>
+      <arg name="margin" type="fixed"/>
+    </request>
   </interface>
 </protocol>