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Qt Integration#

For a complex Qt application based on pymmcore-plus check out napari-micromanager which implements a GUI to control microscopes.

pymmcore-plus is designed seamlessly integrate with Qt GUIs. It accomplishes this in two ways:

  1. pymmcore_plus.CMMCorePlus.run_mda runs in a thread in order to not block the event loop.
  2. The events object will preferentially to use QSignals instead of of signals from the psygnal library. This helps keep things from crashing when working with callbacks in multiple threads.

This example requires qtpy and an Qt backend installed in the env:

pip install qtpy superqt Pyside2 # or pyqt5

Avoiding blocking the Qt event loop#

If you make a blocking call on the thread running the Qt event loop then your GUI will become unresponsive. pymmcore-plus has two options to avoid this. The recommended way is to use threads to call pymmcore_plus.CMMCorePlus.snapImage, and let pymmcore-plus handle the threading when you use pymmcore_plus.CMMCorePlus.run_mda.

This example will use the recommended process-local(threads) approach.

The simple application will consist of a counter that increments so long as the event loop is not blocked, and two buttons to call the snapImage method. One button will call from a thread and the counter should continue, the other will block and will stop the counter.

Key takeaways:

  1. Use CMMCorePlus.instance() to create the core object. This allows another script in the same process to use the same object.
  2. Use a thread for blocking operations like snapImage.
import sys

from qtpy.QtCore import QTimer
from qtpy.QtWidgets import (
    QApplication,
    QLabel,
    QMainWindow,
    QPushButton,
    QVBoxLayout,
    QWidget,
)
from superqt.utils import create_worker

from pymmcore_plus import CMMCorePlus


class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.mmc = CMMCorePlus.instance()
        self.mmc.loadSystemConfiguration()
        self.mmc.setExposure(5000)  # 5 seconds

        self.counter = 0

        layout = QVBoxLayout()

        self.l = QLabel("Start")
        b_blocking = QPushButton("Snap blocking")
        b_threaded = QPushButton("Snap threaded")
        b_blocking.pressed.connect(self.snap_blocking)
        b_threaded.pressed.connect(self.snap_threaded)

        layout.addWidget(self.l)
        layout.addWidget(b_blocking)
        layout.addWidget(b_threaded)

        w = QWidget()
        w.setLayout(layout)
        self.setCentralWidget(w)
        self.show()

        self.timer = QTimer()
        self.timer.setInterval(1000)
        self.timer.timeout.connect(self._recurring_timer)
        self.timer.start()

    def _recurring_timer(self):
        self.counter += 1
        self.l.setText("Counter: %d" % self.counter)

    def snap_threaded(self):
        # alternatively you could use the python threading module
        # or directly use QThreads
        create_worker(
            self._mmc.snapImage,
            _start_thread=True,
        )

    def snap_blocking(self):
        self.mmc.snapImage()



app = QApplication(sys.argv)
window = MainWindow()
app.exec_()