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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 |