Client: Expose a way to set window margins via native interface

The lack of such API is a big hassle to me since a long time.
All that time I was forced to have my own fork of the
xdg-shell plugin in the application code in order to have
shadows on Wayland with custom client-side decorations.
I hope I won't have to maintain the fork anymore.

Pick-to: 6.4
Change-Id: Iaf498469843b5cac5c458049164065c4ef15877d
Reviewed-by: David Edmundson <davidedmundson@kde.org>

src/plugins/platforms/wayland/qwaylandnativeinterface.cpp

@@ -129,6 +129,17 @@ void *QWaylandNativeInterface::nativeResourceForContext(const QByteArray &resour
 }
 #endif  // opengl
 
+QPlatformNativeInterface::NativeResourceForWindowFunction QWaylandNativeInterface::nativeResourceFunctionForWindow(const QByteArray &resource)
+{
+    QByteArray lowerCaseResource = resource.toLower();
+
+    if (lowerCaseResource == "setmargins") {
+        return NativeResourceForWindowFunction(reinterpret_cast<void *>(setWindowMargins));
+    }
+
+    return nullptr;
+}
+
 QVariantMap QWaylandNativeInterface::windowProperties(QPlatformWindow *window) const
 {
     QWaylandWindow *waylandWindow = static_cast<QWaylandWindow *>(window);
@@ -158,6 +169,12 @@ void QWaylandNativeInterface::emitWindowPropertyChanged(QPlatformWindow *window,
     emit windowPropertyChanged(window,name);
 }
 
+void QWaylandNativeInterface::setWindowMargins(QWindow *window, const QMargins &margins)
+{
+    QWaylandWindow *wlWindow = static_cast<QWaylandWindow*>(window->handle());
+    wlWindow->setCustomMargins(margins);
+}
+
 }
 
 QT_END_NAMESPACE

src/plugins/platforms/wayland/qwaylandnativeinterface_p.h

@@ -24,6 +24,8 @@
 
 QT_BEGIN_NAMESPACE
 
+class QMargins;
+
 namespace QtWaylandClient {
 
 class QWaylandIntegration;
@@ -41,6 +43,7 @@ public:
 #if QT_CONFIG(opengl)
     void *nativeResourceForContext(const QByteArray &resource, QOpenGLContext *context) override;
 #endif
+    NativeResourceForWindowFunction nativeResourceFunctionForWindow(const QByteArray &resource) override;
     QVariantMap windowProperties(QPlatformWindow *window) const override;
     QVariant windowProperty(QPlatformWindow *window, const QString &name) const override;
     QVariant windowProperty(QPlatformWindow *window, const QString &name, const QVariant &defaultValue) const override;
@@ -49,6 +52,8 @@ public:
     void emitWindowPropertyChanged(QPlatformWindow *window, const QString &name);
 
 private:
+    static void setWindowMargins(QWindow *window, const QMargins &margins);
+
     QWaylandIntegration *m_integration = nullptr;
     QHash<QPlatformWindow*, QVariantMap> m_windowProperties;
 };

src/plugins/platforms/wayland/qwaylandwindow.cpp

@@ -402,8 +402,12 @@ void QWaylandWindow::resizeFromApplyConfigure(const QSize &sizeWithMargins, cons
     // 2) Following resizeFromApplyConfigure() calls should have sizeWithMargins equal to
     //    windowContentGeometry() which excludes shadows, therefore in this case we have to
     //    exclude them too in order not to accidentally apply smaller size to the window.
-    if (mWindowDecorationEnabled && (sizeWithMargins != surfaceSize()))
+    if (sizeWithMargins != surfaceSize()) {
-        margins = mWindowDecoration->margins(QWaylandAbstractDecoration::ShadowsExcluded);
+        if (mWindowDecorationEnabled)
+            margins = mWindowDecoration->margins(QWaylandAbstractDecoration::ShadowsExcluded);
+        if (!mCustomMargins.isNull())
+            margins -= mCustomMargins;
+    }
 
     int widthWithoutMargins = qMax(sizeWithMargins.width() - (margins.left() + margins.right()), 1);
     int heightWithoutMargins = qMax(sizeWithMargins.height() - (margins.top() + margins.bottom()), 1);
@@ -740,6 +744,12 @@ QMargins QWaylandWindow::clientSideMargins() const
     return mWindowDecorationEnabled ? mWindowDecoration->margins() : QMargins{};
 }
 
+void QWaylandWindow::setCustomMargins(const QMargins &margins) {
+    const QMargins oldMargins = mCustomMargins;
+    mCustomMargins = margins;
+    setGeometry(geometry().marginsRemoved(oldMargins).marginsAdded(margins));
+}
+
 /*!
  * Size, with decorations (including including eventual shadows) in wl_surface coordinates
  */
@@ -759,6 +769,9 @@ QRect QWaylandWindow::windowContentGeometry() const
     if (mWindowDecorationEnabled)
         shadowMargins = mWindowDecoration->margins(QWaylandAbstractDecoration::ShadowsOnly);
 
+    if (!mCustomMargins.isNull())
+        shadowMargins += mCustomMargins;
+
     return QRect(QPoint(shadowMargins.left(), shadowMargins.top()), surfaceSize().shrunkBy(shadowMargins));
 }
 

src/plugins/platforms/wayland/qwaylandwindow_p.h

@@ -112,6 +112,7 @@ public:
     bool waitForFrameSync(int timeout);
 
     QMargins frameMargins() const override;
+    void setCustomMargins(const QMargins &margins);
     QSize surfaceSize() const;
     QRect windowContentGeometry() const;
     QPointF mapFromWlSurface(const QPointF &surfacePosition) const;
@@ -289,6 +290,8 @@ protected:
     QWaylandBuffer *mQueuedBuffer = nullptr;
     QRegion mQueuedBufferDamage;
 
+    QMargins mCustomMargins;
+
 private:
     void setGeometry_helper(const QRect &rect);
     void initWindow();