Disable drag&drop on eglfs for qml app

The drag creates raster window, which on eglfs platform
can be problematic. In case of running qml based
browser without backing store, this will try to create a
backing store during drag event, which will abort on eglfs.
Therefore avoid the drag in qml in case the platform does
not support multiple windows.

This patch has the side effect of disabling drag even
when qml runs with backing store, i.e. using QQuickWidget and
therefore creating another raster window is not an issue.

[ChangeLog][Behavior Changes] Drag&Drop is now disabled for
QML based applications, when platform does not support
multiple top-level windows (like EGLFS).

Task-number: QTBUG-57516
Change-Id: I0c2685ba90914fe1f7168c79744c55e07e589488
Reviewed-by: Kai Koehne <kai.koehne@qt.io>

6 files changed, 21 insertions, 0 deletions

diff --git a/src/core/web_contents_adapter_client.h b/src/core/web_contents_adapter_client.h
index 4c5133772..0469867f2 100644
--- a/src/core/web_contents_adapter_client.h
+++ b/src/core/web_contents_adapter_client.h
@@ -449,6 +449,7 @@ public:
     virtual void updateContentsSize(const QSizeF &size) = 0;
     virtual void startDragging(const content::DropData &dropData, Qt::DropActions allowedActions,
                                const QPixmap &pixmap, const QPoint &offset) = 0;
+    virtual bool supportsDragging() const = 0;
     virtual bool isEnabled() const = 0;
     virtual const QObject *holdingQObject() const = 0;
     virtual void setToolTip(const QString& toolTipText) = 0;
diff --git a/src/core/web_contents_view_qt.cpp b/src/core/web_contents_view_qt.cpp
index a7895d61c..6b68a9569 100644
--- a/src/core/web_contents_view_qt.cpp
+++ b/src/core/web_contents_view_qt.cpp
@@ -232,6 +232,12 @@ void WebContentsViewQt::StartDragging(const content::DropData &drop_data,
 #if QT_CONFIG(draganddrop)
     Q_UNUSED(event_info);
 
+    if (!m_client->supportsDragging()) {
+        if (source_rwh)
+            source_rwh->DragSourceSystemDragEnded();
+        return;
+    }
+
     QPixmap pixmap;
     QPoint hotspot;
     pixmap = QPixmap::fromImage(toQImage(image.GetRepresentation(m_client->dpiScale())));
diff --git a/src/webengine/api/qquickwebengineview.cpp b/src/webengine/api/qquickwebengineview.cpp
index fde7b40dc..babfbd014 100644
--- a/src/webengine/api/qquickwebengineview.cpp
+++ b/src/webengine/api/qquickwebengineview.cpp
@@ -1012,6 +1012,13 @@ void QQuickWebEngineViewPrivate::startDragging(const content::DropData &dropData
 #endif // QT_CONFIG(draganddrop)
 }
 
+bool QQuickWebEngineViewPrivate::supportsDragging() const
+{
+    // QTBUG-57516
+    // Fixme: This is just a band-aid workaround.
+    return QGuiApplicationPrivate::platformIntegration()->hasCapability(QPlatformIntegration::MultipleWindows);
+}
+
 bool QQuickWebEngineViewPrivate::isEnabled() const
 {
     const Q_Q(QQuickWebEngineView);
diff --git a/src/webengine/api/qquickwebengineview_p_p.h b/src/webengine/api/qquickwebengineview_p_p.h
index 73607aa59..1723da7ea 100644
--- a/src/webengine/api/qquickwebengineview_p_p.h
+++ b/src/webengine/api/qquickwebengineview_p_p.h
@@ -144,6 +144,7 @@ public:
     void updateContentsSize(const QSizeF &size) override;
     void startDragging(const content::DropData &dropData, Qt::DropActions allowedActions,
                        const QPixmap &pixmap, const QPoint &offset) override;
+    bool supportsDragging() const override;
     bool isEnabled() const override;
     void setToolTip(const QString &toolTipText) override;
     const QObject *holdingQObject() const override;
diff --git a/src/webenginewidgets/api/qwebenginepage.cpp b/src/webenginewidgets/api/qwebenginepage.cpp
index 8911c63c8..3d0964895 100644
--- a/src/webenginewidgets/api/qwebenginepage.cpp
+++ b/src/webenginewidgets/api/qwebenginepage.cpp
@@ -1673,6 +1673,11 @@ void QWebEnginePagePrivate::startDragging(const content::DropData &dropData,
 #endif // QT_CONFIG(draganddrop)
 }
 
+bool QWebEnginePagePrivate::supportsDragging() const
+{
+    return true;
+}
+
 bool QWebEnginePagePrivate::isEnabled() const
 {
     const Q_Q(QWebEnginePage);
diff --git a/src/webenginewidgets/api/qwebenginepage_p.h b/src/webenginewidgets/api/qwebenginepage_p.h
index dc7d02b73..fde877255 100644
--- a/src/webenginewidgets/api/qwebenginepage_p.h
+++ b/src/webenginewidgets/api/qwebenginepage_p.h
@@ -142,6 +142,7 @@ public:
     void updateContentsSize(const QSizeF &size) override;
     void startDragging(const content::DropData &dropData, Qt::DropActions allowedActions,
                        const QPixmap &pixmap, const QPoint &offset) override;
+    bool supportsDragging() const override;
     bool isEnabled() const override;
     void setToolTip(const QString &toolTipText) override;
     const QObject *holdingQObject() const override;