3 files changed, 47 insertions, 49 deletions
diff --git a/examples/widgets/painting/plot/doc/plot.png b/examples/widgets/painting/plot/doc/plot.png
new file mode 100644
index 000000000..e5031e351
--- /dev/null
+++ b/examples/widgets/painting/plot/doc/plot.png
diff --git a/examples/widgets/painting/plot/doc/plot.rst b/examples/widgets/painting/plot/doc/plot.rst
new file mode 100644
index 000000000..a63eaed87
--- /dev/null
+++ b/examples/widgets/painting/plot/doc/plot.rst
@@ -0,0 +1,36 @@
+Plot Example
+============
+
+The Plot example shows how to display a graph from data using an
+`opaque container <https://doc.qt.io/qtforpython-6/shiboken6/typesystem_containers.html>`_.
+
+It draws an sine graph using ``QPainter.drawPolyline()`` from a list of points.
+The list of points is continuously updated, as is the case for a example for a
+graph of an oscilloscope or medical patient monitor.
+In this case, it makes sense from a performance point of view to avoid the
+conversion of a Python list of data to a C++ list (``QList<QPoint>``)
+for each call to the plot function ``QPainter.drawPolyline()``.
+This is where opaque containers come into play.
+
+Instead of Python list of points, a ``QPointList`` is instantiated to store
+the data. ``QPointList`` is an opaque container wrapping a ``QList<QPoint>``.
+It can be passed to ``QPainter.drawPolyline()`` instead of a Python list of
+points.
+
+The type is declared in the entry for the ``QList`` container type in the
+type system file of the ``QtCore`` library:
+
+.. code-block:: xml
+
+    <container-type name="QList" type="list"
+                    opaque-containers="int:QIntList;QPoint:QPointList;QPointF:QPointFList">
+        ...
+    </container-type>
+
+In the ``shift()`` member function, new data are appended to the list while
+old data moving out of the visible window are removed from the front of the
+list.
+
+.. image:: plot.png
+   :width: 400
+   :alt: Plot Screenshot
diff --git a/examples/widgets/painting/plot/plot.py b/examples/widgets/painting/plot/plot.py
index 156a6408d..d437309d0 100644
--- a/examples/widgets/painting/plot/plot.py
+++ b/examples/widgets/painting/plot/plot.py
@@ -1,50 +1,13 @@
-#############################################################################
-##
-## Copyright (C) 2021 The Qt Company Ltd.
-## Contact: https://www.qt.io/licensing/
-##
-## This file is part of the Qt for Python examples of the Qt Toolkit.
-##
-## $QT_BEGIN_LICENSE:BSD$
-## You may use this file under the terms of the BSD license as follows:
-##
-## "Redistribution and use in source and binary forms, with or without
-## modification, are permitted provided that the following conditions are
-## met:
-##   * Redistributions of source code must retain the above copyright
-##     notice, this list of conditions and the following disclaimer.
-##   * Redistributions in binary form must reproduce the above copyright
-##     notice, this list of conditions and the following disclaimer in
-##     the documentation and/or other materials provided with the
-##     distribution.
-##   * Neither the name of The Qt Company Ltd nor the names of its
-##     contributors may be used to endorse or promote products derived
-##     from this software without specific prior written permission.
-##
-##
-## THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-## "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-## LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-## A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-## OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-## SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-## LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-## DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-## THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-## (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-## OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
-##
-## $QT_END_LICENSE$
-##
-#############################################################################
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+from __future__ import annotations
 
 import math
 import sys
 
 from PySide6.QtWidgets import QWidget, QApplication
-from PySide6.QtCore import QPoint, QRect, QTimer, Qt, Slot
-from PySide6.QtGui import (QColor, QPainter, QPaintEvent, QPen, QPointList,
-                           QTransform)
+from PySide6.QtCore import QPoint, QRect, QTimer, Qt
+from PySide6.QtGui import QPainter, QPointList
 
 
 WIDTH = 680
@@ -63,6 +26,7 @@ class PlotWidget(QWidget):
         self._timer.timeout.connect(self.shift)
 
         self._points = QPointList()
+        self._points.reserve(WIDTH)
         self._x = 0
         self._delta_x = 0.05
         self._half_height = HEIGHT / 2
@@ -87,13 +51,11 @@ class PlotWidget(QWidget):
         self.update()
 
     def paintEvent(self, event):
-        painter = QPainter()
-        painter.begin(self)
-        rect = QRect(QPoint(0, 0), self.size())
-        painter.fillRect(rect, Qt.white)
-        painter.translate(-self._points[0].x(), 0)
-        painter.drawPolyline(self._points)
-        painter.end()
+        with QPainter(self) as painter:
+            rect = QRect(QPoint(0, 0), self.size())
+            painter.fillRect(rect, Qt.white)
+            painter.translate(-self._points[0].x(), 0)
+            painter.drawPolyline(self._points)
 
 
 if __name__ == "__main__":