qml: Layout the drop area and title bar inside the FloatingWindow

We could just control geometry of the c++ title bar and geometry,
but then the user wouldn't be able to style it, and users rather
style things in QML than subclassing FloatingWindow and writing C++.

So instance some .qml files to represent the drop area and floating
window, so user can muck with.

Hierarchy looks like this now:

-QQuickWindow
--FloatingWindowQuick (C++ QQuickItem)
---FloatingWindow.qml
----TitleBar.qml (reads state from TitleBar c++)
----DropArea.qml
-----DropArea (C++ QQuickItem)
------Frame
      etc

src/private/FloatingWindow_p.h

@@ -30,10 +30,13 @@ class DropArea;
 class Frame;
 class MultiSplitter;
 
-class DOCKS_EXPORT FloatingWindow : public QWidgetAdapter
-    , public Draggable
+class DOCKS_EXPORT FloatingWindow
+        : public QWidgetAdapter
+        , public Draggable
 {
     Q_OBJECT
+    Q_PROPERTY(KDDockWidgets::TitleBar* titleBar READ titleBar CONSTANT)
+    Q_PROPERTY(KDDockWidgets::DropArea* dropArea READ dropArea CONSTANT)
 public:
     explicit FloatingWindow(MainWindowBase *parent = nullptr);
     explicit FloatingWindow(Frame *frame, MainWindowBase *parent = nullptr);

src/private/quick/FloatingWindowQuick.cpp

@@ -40,6 +40,14 @@ void FloatingWindowQuick::init()
 {
     m_quickWindow->setResizeMode(QQuickView::SizeViewToRootObject);
     QWidgetAdapter::setParent(m_quickWindow->contentItem());
+
+    QQuickItem *visualItem = createItem(Config::self().qmlEngine(), QStringLiteral("qrc:/kddockwidgets/private/quick/qml/FloatingWindow.qml"));
+    Q_ASSERT(visualItem);
+    visualItem->setParent(this);
+    visualItem->setParentItem(this);
+
+    //dropArea()->QWidgetAdapter::setParent(visualItem);
+
     m_quickWindow->setFlags(windowFlags());
     m_quickWindow->show();
     m_quickWindow->setGeometry(200, 200, 800, 800);  // TODO: remove

src/private/quick/QWidgetAdapter_quick.cpp

@@ -24,6 +24,9 @@
 #include <QResizeEvent>
 #include <QMouseEvent>
 #include <QWindow>
+#include <QQmlComponent>
+#include <QQuickItem>
+#include <QQmlEngine>
 
 using namespace KDDockWidgets;
 
@@ -211,6 +214,18 @@ Qt::WindowFlags QWidgetAdapter::windowFlags() const
     return m_requestedWindowFlags;
 }
 
+QQuickItem *QWidgetAdapter::createItem(QQmlEngine *engine, const QString &filename) const
+{
+    QQmlComponent component(engine, filename);
+    QObject *obj = component.create();
+    if (!obj) {
+        qWarning() << Q_FUNC_INFO << component.errorString();
+        return nullptr;
+    }
+
+    return qobject_cast<QQuickItem*>(obj);
+}
+
 void QWidgetAdapter::setFlag(Qt::WindowType f, bool on)
 {
     if (QWindow *w = windowHandle()) {

src/private/quick/QWidgetAdapter_quick_p.h

@@ -30,32 +30,12 @@
 
 QT_BEGIN_NAMESPACE
 class QWindow;
+class QQmlEngine;
 QT_END_NAMESPACE
 
 namespace KDDockWidgets {
 
 class FloatingWindow;
-/*
-class QuickItem : public QQuickItem
-{
-public:
-    explicit QuickItem(QQuickItem *parent)
-        : QQuickItem(parent)
-    {
-    }
-    ~QuickItem() override;
-
-    QRect geometry() const { return {}; }
-    void setGeometry(QRect) {}
-
-    void releaseMouse()
-    {
-        ungrabMouse();
-    }
-};
-QuickItem::~QuickItem() {}
-*/
-
 class DOCKS_EXPORT QWidgetAdapter : public QQuickItem
 {
     Q_OBJECT
@@ -125,9 +105,9 @@ public:
 
     Qt::WindowFlags windowFlags() const;
 
+    QQuickItem *createItem(QQmlEngine *, const QString &filename) const;
 protected:
     void raiseAndActivate();
-
     virtual bool onResize(QSize newSize);
     virtual void onLayoutRequest();
     virtual void onMousePress();

src/private/quick/QmlTypes.cpp

@@ -24,4 +24,5 @@ void KDDockWidgets::registerQmlTypes()
     qmlRegisterType<MainWindowQuick>("com.kdab.dockwidgets", 1, 0, "MainWindowQuick");
 
     qmlRegisterUncreatableType<TitleBar>("com.kdab.dockwidgets", 1, 0, "TitleBar", QStringLiteral("Enum access only"));
+    qRegisterMetaType<DropArea*>();
 }

src/private/quick/qml/DropArea.qml

@@ -0,0 +1,18 @@
+/*
+  This file is part of KDDockWidgets.
+
+  SPDX-FileCopyrightText: 2019-2020 Klarälvdalens Datakonsult AB, a KDAB Group company <info@kdab.com>
+  Author: Sérgio Martins <sergio.martins@kdab.com>
+
+  SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only
+
+  Contact KDAB at <info@kdab.com> for commercial licensing options.
+*/
+
+import QtQuick 2.9
+
+Rectangle {
+    id: root
+    property QtObject dropAreaCpp: null
+    color: "orange"
+}

src/private/quick/qml/FloatingWindow.qml

@@ -0,0 +1,52 @@
+/*
+  This file is part of KDDockWidgets.
+
+  SPDX-FileCopyrightText: 2019-2020 Klarälvdalens Datakonsult AB, a KDAB Group company <info@kdab.com>
+  Author: Sérgio Martins <sergio.martins@kdab.com>
+
+  SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only
+
+  Contact KDAB at <info@kdab.com> for commercial licensing options.
+*/
+
+import QtQuick 2.9
+import "." as KDDW
+
+Rectangle {
+    id: root
+    readonly property QtObject floatingWindowCpp: parent
+    readonly property QtObject titleBarCpp: floatingWindowCpp ? floatingWindowCpp.titleBar : null
+    readonly property QtObject dropAreaCpp: floatingWindowCpp ? floatingWindowCpp.dropArea : null
+
+    color: "yellow"
+    anchors.fill: parent
+
+    KDDW.TitleBar {
+        id: titleBar
+        height: 30
+        titleBarCpp: root.titleBarCpp
+
+        anchors {
+            top:  parent.top
+            left: parent.left
+            right: parent.right
+        }
+    }
+
+    KDDW.DropArea {
+        id: dropArea
+        dropAreaCpp: root.dropAreaCpp
+        anchors {
+            left: parent.left
+            right: parent.right
+            top: titleBar.bottom
+            bottom: parent.bottom
+        }
+    }
+
+    onDropAreaCppChanged: {
+        // Parent the cpp obj to the visual obj. So the user can style it
+        dropAreaCpp.parent = dropArea;
+        dropAreaCpp.anchors.fill = dropArea;
+    }
+}

src/private/quick/qml/Frame.qml

@@ -14,13 +14,15 @@ import QtQuick 2.9
 Rectangle {
     id: root
     property QtObject frameCpp
+    readonly property QtObject titleBarCpp: frameCpp ? frameCpp.titleBar : null
 
     color: "cyan"
     anchors.fill: parent
 
     TitleBar {
         height: 30
-        titleBarCpp: frameCpp ? frameCpp.titleBar : null
+        titleBarCpp: root.titleBarCpp
+        visible: true
         anchors {
             top:  parent.top
             left: parent.left

src/qtquick.qrc

@@ -1,5 +1,7 @@
 <RCC>
     <qresource prefix="/kddockwidgets/">
+        <file>private/quick/qml/DropArea.qml</file>
+        <file>private/quick/qml/FloatingWindow.qml</file>
         <file>private/quick/qml/Frame.qml</file>
         <file>private/quick/qml/MainWindow.qml</file>
         <file>private/quick/qml/Separator.qml</file>