Add multiwindow functionality from the C++ example

Pick-to: 6.6
Task-number: PYSIDE-2460
Task-number: PYSIDE-2206
Change-Id: I6644e098c15885271bd4bc1188ae44e6c984b369
Reviewed-by: Shyamnath Premnadh <Shyamnath.Premnadh@qt.io>

5 files changed, 110 insertions, 13 deletions

diff --git a/examples/opengl/hellogl2/doc/hellogl2.rst b/examples/opengl/hellogl2/doc/hellogl2.rst
index 1223e138c..3471ebf30 100644
--- a/examples/opengl/hellogl2/doc/hellogl2.rst
+++ b/examples/opengl/hellogl2/doc/hellogl2.rst
@@ -4,6 +4,20 @@ Hello GL2 Example
 The Hello GL2 example demonstrates the basic use of the OpenGL-related classes
 provided with Qt.
 
+In this example the widget's corresponding top-level window can change several
+times during the widget's lifetime. Whenever this happens, the QOpenGLWidget's
+associated context is destroyed and a new one is created, requiring us to clean
+up the GL resources.
+
+The equivalent C++ example does this cleanup on emission of the
+QOpenGLContext.aboutToBeDestroyed() signal. However, in Qt for Python, we
+cannot rely on this signal when it is emitted from the destructor.
+
+Therefore, we do the cleanup in GLWidget.hideEvent().
+
+This will be followed by an invocation of initializeGL() where we can recreate
+all resources.
+
 .. image:: hellogl2.png
    :width: 400
    :alt: Hello GL2 Screenshot
diff --git a/examples/opengl/hellogl2/hellogl2.pyproject b/examples/opengl/hellogl2/hellogl2.pyproject
index c9cd23c97..d85a139e4 100644
--- a/examples/opengl/hellogl2/hellogl2.pyproject
+++ b/examples/opengl/hellogl2/hellogl2.pyproject
@@ -1,3 +1,3 @@
 {
-    "files": ["main.py", "glwidget.py", "logo.py", "window.py"]
+    "files": ["main.py", "glwidget.py", "logo.py", "mainwindow.py", "window.py"]
 }
diff --git a/examples/opengl/hellogl2/main.py b/examples/opengl/hellogl2/main.py
index ea35c0077..c7eb78a82 100644
--- a/examples/opengl/hellogl2/main.py
+++ b/examples/opengl/hellogl2/main.py
@@ -12,7 +12,7 @@ from PySide6.QtWidgets import (QApplication, QMessageBox)
 
 
 try:
-    from window import Window
+    from mainwindow import MainWindow
     from glwidget import GLWidget
 except ImportError:
     app = QApplication(sys.argv)
@@ -47,12 +47,11 @@ if __name__ == '__main__':
 
     GLWidget.set_transparent(options.transparent)
 
-    main_window = Window()
+    main_window = MainWindow()
     if options.transparent:
         main_window.setAttribute(Qt.WA_TranslucentBackground)
         main_window.setAttribute(Qt.WA_NoSystemBackground, False)
 
-    main_window.resize(main_window.sizeHint())
     main_window.show()
 
     res = app.exec()
diff --git a/examples/opengl/hellogl2/mainwindow.py b/examples/opengl/hellogl2/mainwindow.py
new file mode 100644
index 000000000..d19053a26
--- /dev/null
+++ b/examples/opengl/hellogl2/mainwindow.py
@@ -0,0 +1,29 @@
+# Copyright (C) 2023 The Qt Company Ltd.
+# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+from PySide6.QtCore import Slot, Qt
+from PySide6.QtGui import QKeySequence
+from PySide6.QtWidgets import QMainWindow, QMessageBox
+
+from window import Window
+
+
+class MainWindow(QMainWindow):
+
+    def __init__(self):
+        super().__init__()
+        menuWindow = self.menuBar().addMenu("Window")
+        menuWindow.addAction("Add new", QKeySequence(Qt.CTRL | Qt.Key_N),
+                             self.onAddNew)
+        menuWindow.addAction("Quit", QKeySequence(Qt.CTRL | Qt.Key_Q),
+                             qApp.closeAllWindows)
+
+        self.onAddNew()
+
+    @Slot()
+    def onAddNew(self):
+        if not self.centralWidget():
+            self.setCentralWidget(Window(self))
+        else:
+            QMessageBox.information(self, "Cannot Add Window()",
+                                    "Already occupied. Undock first.")
diff --git a/examples/opengl/hellogl2/window.py b/examples/opengl/hellogl2/window.py
index 0d38fc490..c7b9946e0 100644
--- a/examples/opengl/hellogl2/window.py
+++ b/examples/opengl/hellogl2/window.py
@@ -2,15 +2,28 @@
 # Copyright (C) 2013 Riverbank Computing Limited.
 # SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 
-from PySide6.QtCore import Qt
-from PySide6.QtWidgets import (QHBoxLayout, QSlider, QWidget)
+from PySide6.QtCore import Slot, Qt
+from PySide6.QtGui import QGuiApplication
+from PySide6.QtWidgets import (QApplication, QHBoxLayout, QMainWindow,
+                               QMessageBox, QPushButton, QSlider,
+                               QVBoxLayout, QWidget)
 
 from glwidget import GLWidget
 
 
+def _main_window():
+    for t in qApp.topLevelWidgets():
+        if isinstance(t, QMainWindow):
+            return t
+    return None
+
+
 class Window(QWidget):
+    instances = []  # Keep references when undocked
+
     def __init__(self, parent=None):
         super().__init__(parent)
+        self.instances.append(self)
 
         self._gl_widget = GLWidget()
 
@@ -26,12 +39,18 @@ class Window(QWidget):
         self._z_slider.valueChanged.connect(self._gl_widget.set_zrotation)
         self._gl_widget.z_rotation_changed.connect(self._z_slider.setValue)
 
-        main_layout = QHBoxLayout()
-        main_layout.addWidget(self._gl_widget)
-        main_layout.addWidget(self._x_slider)
-        main_layout.addWidget(self._y_slider)
-        main_layout.addWidget(self._z_slider)
-        self.setLayout(main_layout)
+        mainLayout = QVBoxLayout(self)
+        w = QWidget()
+        container = QHBoxLayout(w)
+        container.addWidget(self._gl_widget)
+        container.addWidget(self._x_slider)
+        container.addWidget(self._y_slider)
+        container.addWidget(self._z_slider)
+
+        mainLayout.addWidget(w)
+        self._dock_btn = QPushButton("Undock")
+        self._dock_btn.clicked.connect(self.dock_undock)
+        mainLayout.addWidget(self._dock_btn)
 
         self._x_slider.setValue(15 * 16)
         self._y_slider.setValue(345 * 16)
@@ -49,8 +68,44 @@ class Window(QWidget):
         slider.setTickPosition(QSlider.TicksRight)
         return slider
 
+    def closeEvent(self, event):
+        self.instances.remove(self)
+        event.accept()
+
     def keyPressEvent(self, event):
-        if event.key() == Qt.Key_Escape:
+        if self.isWindow() and event.key() == Qt.Key_Escape:
             self.close()
         else:
             super().keyPressEvent(event)
+
+    @Slot()
+    def dock_undock(self):
+        if self.parent():
+            self.undock()
+        else:
+            self.dock()
+
+    def dock(self):
+        mainWindow = _main_window()
+        if not mainWindow or not mainWindow.isVisible():
+            QMessageBox.information(self, "Cannot Dock",
+                                    "Main window already closed")
+            return
+        if mainWindow.centralWidget():
+            QMessageBox.information(self, "Cannot Dock",
+                                    "Main window already occupied")
+            return
+
+        self.setAttribute(Qt.WA_DeleteOnClose, False)
+        self._dock_btn.setText("Undock")
+        mainWindow.setCentralWidget(self)
+
+    def undock(self):
+        self.setParent(None)
+        self.setAttribute(Qt.WA_DeleteOnClose)
+        geometry = self.screen().availableGeometry()
+        x = geometry.x() + (geometry.width() - self.width()) / 2
+        y = geometry.y() + (geometry.height() - self.height()) / 2
+        self.move(x, y)
+        self._dock_btn.setText("Dock")
+        self.show()