How to display image on secondary monitor in full screen?

Question

How can I use PyQt5/PySide or any other Python library to display a desired image on a secondary monitor in full-screen mode? In the past, I used a framebuffer image viewer (Fbi and Fbi improved). However, this approach requires me to use Linux. I prefer to work in Windows and preferably find a solution using Python.

Motivation/Context

I am working on a DLP projection based 3D printing process. When I connect a DLP projector to my Windows PC using HDMI, it shows up as a second monitor. I want to dedicate this secondary monitor (DLP) only to display my desired patterns images (png, bmp, or svg) for the 3D printing process. I would like to programmatically control using Python which image is being displayed. This is a followup question to https://3dprinting.stackexchange.com/questions/1217/how-to-display-images-on-dlp-using-hdmi-for-3d-printing

Partial solution and issues

Below code is one possible solution, however I am unsure if its the correct or the most efficient approach. I found two approaches using PyQt5: 1) using splash screen, and 2) using QLabel. I am facing the following issues with my code:

• Cursor is hidden as expected, however if I accidentally click mouse on secondary screen, the splash screen closes.
• If I use the QLabel approach, I see a white screen appear and then my image gets loaded. There is a distinct delay of ~ 0.5-1s from the time white screen appears to when the actual image is displayed.
• If the images are displayed in high frequency (ex: every 1 sec), this code doesn't work well. For example, in the code change the total_loops=1 to total_loops=25. When using splash screen method, I see the splash screen appear on the main screen then it moves to the secondary screen. When using the QLabel method, all I see is a white screen appear, and only the last iteration the image is displayed. In addition, the window of the QLabel becomes active on the main screen and is visible in the Task bar.
• How do I handle a situation if I want to display a video instead of an image?

For 3D printing application, the solution needs to meet the following requirement:

• Secondary screen is the DLP projector, and it should NOT contain any OS related windows/taskbars/etc...
• No cursor/mouse or other applications should appear on the the secondary screen
• Images/videos need to be displayed in fullscreen mode
• When displaying or updating images on the secondary screen, there should be no disturbance on the primary screen. For example, the image window in secondary screen shouldn't take focus away from currently active window in the primary screen

import time
start_time = time.time() 
import sys
from PyQt5.QtWidgets import QApplication, QLabel, QSplashScreen
from PyQt5.QtGui import QPixmap, QCursor
from PyQt5.QtCore import Qt
import os 

app = QApplication(sys.argv)

total_loops = 1

for i in range(total_loops):    

    # https://doc.qt.io/qtforpython/index.html
    # https://www.riverbankcomputing.com/static/Docs/PyQt5/module_index.html

    s = app.screens()[1] # Get the secondary screen 
    # Display info about secondary screen 
    print('Screen Name: {} Size: {}x{} Available geometry {}x{} '.format(s.name(), s.size().width(), s.size().height(), s.availableGeometry().width(), s.availableGeometry().height()))

    # Hide cursor from appearing on screen 
    app.setOverrideCursor(QCursor(Qt.BlankCursor)) # https://forum.qt.io/topic/49877/hide-cursor 

    # Select desired image to be displayed 
    pixmap = QPixmap('test.png')

    # Splash screen approach 
    # https://doc.qt.io/qtforpython/PySide2/QtWidgets/QSplashScreen.html?highlight=windowflags 
    splash = QSplashScreen(pixmap)      # Set the splash screen to desired image
    splash.show()                       # Show the splash screen
    splash.windowHandle().setScreen(s)  # Set splash screen to secondary monitor https://stackoverflow.com/a/30597458/4988010
    splash.showFullScreen()             # Show in splash screen in full screen mode 

    # # Qlabel apporach 
    # l = QLabel()
    # l.setPixmap(pixmap)
    # l.move(1920,0)
    # l.show()
    # l.windowHandle().setScreen(s) # https://stackoverflow.com/a/30597458/4988010
    # l.showFullScreen()

    time.sleep(0.5) 
    end_time = time.time() 
    print('Execution  time: ', end_time-start_time )

sys.exit(app.exec_())

Answer 1

The code below is one possible solution to my question. My solution assumes that Qt is only used to display the images in full-screen and not for the remaining logic. Therefore, I had to run the QT app in a secondary thread. This is because the moment I run the function app.exec_(), Qt will continuously run an event loop thus blocking the rest of my Python logic which does NOT rely on Qt. It is my understanding running QApplication outside of a main thread is not recommended, therefore I would welcome a more experienced user to post a better approach.

from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
from PyQt5.QtCore import QObject, pyqtSignal
import sys
import time
import threading


def main():

    print('Step 1')
    print('     Some logic here without QT')

    print('Step 2')
    print('     Launch QT app to run in background')
    myapp = myImageDisplayApp()

    print('Step 3')
    print('     Continue some logic while QT running in background')
    time.sleep(2)

    print('Step 4')
    print('     Update the displayed image in the QT app running in background')
    myapp.emit_image_update('qt_test_static_1.png')
    time.sleep(2)

    print('Step 5')
    print('     Update displayed image again')
    myapp.emit_image_update('qt_test_static_2.png')
    time.sleep(2)

class myImageDisplayApp (QObject):

    # Define the custom signal
    # https://www.riverbankcomputing.com/static/Docs/PyQt5/signals_slots.html#the-pyqtslot-decorator
    signal_update_image = pyqtSignal(str)

    def __init__ (self):

        super().__init__()

        # Setup the seperate thread 
        # https://stackoverflow.com/a/37694109/4988010
        self.thread = threading.Thread(target=self.run_app_widget_in_background) 
        self.thread.daemon = True
        self.thread.start()

    def run_app_widget_in_background(self):
        self.app = QApplication(sys.argv)
        self.my_bg_qt_app = qtAppWidget(main_thread_object=self)
        self.app.exec_()

    def emit_image_update(self, pattern_file=None):
        print('emit_image_update signal')
        self.signal_update_image.emit(pattern_file)


class qtAppWidget (QLabel):

    def __init__ (self, main_thread_object):

        super().__init__()

        # Connect the singal to slot
        main_thread_object.signal_update_image.connect(self.updateImage)

        self.setupGUI()

    def setupGUI(self):

        self.app = QApplication.instance()

        # Get avaliable screens/monitors
        # https://doc.qt.io/qt-5/qscreen.html
        # Get info on selected screen 
        self.selected_screen = 0            # Select the desired monitor/screen

        self.screens_available = self.app.screens()
        self.screen = self.screens_available[self.selected_screen]
        self.screen_width = self.screen.size().width()
        self.screen_height = self.screen.size().height()

        # Create a black image for init 
        self.pixmap = QPixmap(self.screen_width, self.screen_height)
        self.pixmap.fill(QColor('black'))

        # Create QLabel object
        self.app_widget = QLabel()

        # Varioius flags that can be applied to make displayed window frameless, fullscreen, etc...
        # https://doc.qt.io/qt-5/qt.html#WindowType-enum
        # https://doc.qt.io/qt-5/qt.html#WidgetAttribute-enum
        self.app_widget.setWindowFlags(Qt.FramelessWindowHint | Qt.WindowDoesNotAcceptFocus | Qt.WindowStaysOnTopHint)
        # Hide mouse cursor 
        self.app_widget.setCursor(Qt.BlankCursor)       

        self.app_widget.setGeometry(0, 0, self.screen_width, self.screen_height)            # Set the size of Qlabel to size of the screen
        self.app_widget.setWindowTitle('myImageDisplayApp')
        self.app_widget.setAlignment(Qt.AlignLeft | Qt.AlignTop) #https://doc.qt.io/qt-5/qt.html#AlignmentFlag-enum                         
        self.app_widget.setPixmap(self.pixmap)
        self.app_widget.show()

        # Set the screen on which widget is on
        self.app_widget.windowHandle().setScreen(self.screen)
        # Make full screen 
        self.app_widget.showFullScreen()


    def updateImage(self, pattern_file=None):
        print('Pattern file given: ', pattern_file)
        self.app_widget.clear()                     # Clear all existing content of the QLabel
        self.pixmap = QPixmap(pattern_file)         # Update pixmap with desired image  
        self.app_widget.setPixmap(self.pixmap)      # Show desired image on Qlabel

if __name__ == "__main__":

    main() 

I would also like to thank @ekhumoro for pointing me to QWidget attributes/flags.

Answer 2

You should not run the GUI in other than the main thread since Qt does not guarantee that it works correctly as indicated by the docs. Instead of executing the GUI in another thread, you must execute the other heavy tasks in another thread.

You have to change your approach to classical sequential logic but you must use event-oriented programming where actions are taken before an event, in the case of Qt through signals.

Considering the above, the solution is:

import sys
import time


from PyQt5.QtCore import pyqtSignal, pyqtSlot, QObject, Qt, QThread, QTimer
from PyQt5.QtGui import QColor, QPixmap
from PyQt5.QtWidgets import QApplication, QLabel, QWidget


class TaskManager(QObject):
    task3Finished = pyqtSignal()
    task4Finished = pyqtSignal()

    @pyqtSlot()
    def task3(self):
        print("Step 3")
        print("     Continue some logic while QT running in background")
        time.sleep(2)
        self.task3Finished.emit()

    @pyqtSlot()
    def task4(self):
        print("Step 4")
        print("     Update the displayed image in the QT app running in background")
        time.sleep(2)
        self.task4Finished.emit()


class qtAppWidget(QWidget):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.setupGUI()

    def setupGUI(self):
        self.app = QApplication.instance()

        # Get avaliable screens/monitors
        # https://doc.qt.io/qt-5/qscreen.html
        # Get info on selected screen
        self.selected_screen = 0  # Select the desired monitor/screen

        self.screens_available = self.app.screens()
        self.screen = self.screens_available[self.selected_screen]
        self.screen_width = self.screen.size().width()
        self.screen_height = self.screen.size().height()

        # Create a black image for init
        self.pixmap = QPixmap(self.screen_width, self.screen_height)
        self.pixmap.fill(QColor("black"))

        # Create QLabel object
        self.app_widget = QLabel()

        # Varioius flags that can be applied to make displayed window frameless, fullscreen, etc...
        # https://doc.qt.io/qt-5/qt.html#WindowType-enum
        # https://doc.qt.io/qt-5/qt.html#WidgetAttribute-enum
        self.app_widget.setWindowFlags(
            Qt.FramelessWindowHint
            | Qt.WindowDoesNotAcceptFocus
            | Qt.WindowStaysOnTopHint
        )
        # Hide mouse cursor
        self.app_widget.setCursor(Qt.BlankCursor)

        self.app_widget.setGeometry(
            0, 0, self.screen_width, self.screen_height
        )  # Set the size of Qlabel to size of the screen
        self.app_widget.setWindowTitle("myImageDisplayApp")
        self.app_widget.setAlignment(
            Qt.AlignLeft | Qt.AlignTop
        )  # https://doc.qt.io/qt-5/qt.html#AlignmentFlag-enum
        self.app_widget.setPixmap(self.pixmap)
        self.app_widget.show()

        # Set the screen on which widget is on
        self.app_widget.windowHandle().setScreen(self.screen)
        # Make full screen
        self.app_widget.show()

    @pyqtSlot()
    def on_task3_finished(self):
        pixmap = QPixmap("qt_test_static_1.png")
        self.app_widget.setPixmap(pixmap)

    @pyqtSlot()
    def on_task4_finished(self):
        pixmap = QPixmap("qt_test_static_2.png")
        self.app_widget.setPixmap(pixmap)

        # quit application after to 2 secons
        QTimer.singleShot(2 * 1000, QApplication.quit)


def main(args):
    print("Step 1")
    print("     Some logic here without QT")

    print("Step 2")
    print("     Launch QT app to run")
    app = QApplication(args)
    myapp = qtAppWidget()

    thread = QThread()
    thread.start()

    manager = TaskManager()
    # move the QObject to the other thread
    manager.moveToThread(thread)

    manager.task3Finished.connect(myapp.on_task3_finished)
    manager.task3Finished.connect(manager.task4)
    manager.task4Finished.connect(myapp.on_task4_finished)

    # start task
    QTimer.singleShot(0, manager.task3)

    ret = app.exec_()

    thread.quit()
    thread.wait()

    del thread, app

    return ret


if __name__ == "__main__":

    sys.exit(main(sys.argv))