:orphan:

Qt Interactive
==============

*Example script* (scamp): `examples/Interactivity & visualization/Responding to a GUI/qt_interactive.py <https://github.com/MarcTheSpark/scamp/blob/main/examples/Interactivity%20%26%20visualization/Responding%20to%20a%20GUI/qt_interactive.py>`__

*Download:* :download:`qt_interactive.py <downloads/interactivity_visualization_responding_to_a_gui_qt_interactive/qt_interactive.py>`

A draggable PyQt rectangle drives live playback in a server session. Moving the rectangle fires a callback that sets the tempo of the clock running the note loop; its vertical position still sets the pitch.

*Topics:* :doc:`Interactivity & visualization › Responding to a GUI <interactivity_visualization>`

.. raw:: html

   <iframe src="https://www.youtube-nocookie.com/embed/DPHPA2dllAQ" style="width:100%;max-width:640px;aspect-ratio:16/9;border:0;display:block;margin:0.6em 0" allowfullscreen></iframe>

.. code-block:: python

   from scamp import *

   from PyQt5 import QtCore, QtWidgets


   class DraggableRect(QtWidgets.QGraphicsRectItem):
       """Movable rectangle that calls `on_move(x, y)` each time it is dragged."""

       def __init__(self, rect, on_move=None):
           super().__init__(rect)
           self.setFlag(QtWidgets.QGraphicsItem.ItemIsMovable, True)
           self.setFlag(QtWidgets.QGraphicsItem.ItemSendsGeometryChanges, True)
           self.on_move = on_move

       def itemChange(self, change, value):
           if change == QtWidgets.QGraphicsItem.ItemPositionChange and self.on_move is not None:
               self.on_move(value.x(), value.y())
           return super().itemChange(change, value)


   class MainWindow(QtWidgets.QMainWindow):
       def __init__(self, parent=None):
           super(MainWindow, self).__init__(parent)
           scene = QtWidgets.QGraphicsScene(self)
           view = QtWidgets.QGraphicsView(scene)
           scene.setSceneRect(QtCore.QRectF(0, 0, 800, 800))

           self.setCentralWidget(view)

           self.rect_item = DraggableRect(QtCore.QRectF(0, 0, 100, 100))
           scene.addItem(self.rect_item)


   if __name__ == '__main__':
       import sys
       app = QtWidgets.QApplication(sys.argv)
       w = MainWindow()
       w.setFixedSize(QtCore.QSize(800, 800))
       w.show()

       # map the rectangle's x position (0–800) to a tempo in BPM
       tempo_response = Envelope([30, 600], [800], [3])

       # leaving the `with` block kills the session (and the forked note loop), so closing
       # the window shuts everything down gracefully rather than leaking the scheduler thread
       with Session().run_as_server() as s:
           piano = s.new_part("piano")
           s.start_transcribing()

           def play_notes():
               while True:
                   piano.play_note((1 - w.rect_item.y() / 800) * 40 + 60, 1.0, 1.0)

           play_clock = s.fork(play_notes)

           # whenever the rectangle moves, retune the note loop's tempo from its x position
           w.rect_item.on_move = lambda x, y: setattr(play_clock, "tempo", tempo_response.value_at(x))

           app.exec_()  # blocks until the window is closed

           performance = s.stop_transcribing()

       performance.to_score().show()