Pygame not detecting duplicate keyboard input events-CodePudding

We're building a hardware device using a raspberry pi with a barcode scanner and a display. The barcode scanner functions like a USB keyboard, and sends keystrokes in quick succession after scanning a barcode. We're having a problem with pygame not detecting duplicate keys from the scanner in quick succession. When running the below code, pygame often misses duplicate keys. Example output from scanning the same barcode:

If I comment out the last three lines however (not updating the screen), the code is scanned successfully every time.

We're using pygame 2.1.2 with python 3.9.2 on a raspberry pi.

import sys, pygame
pygame.init()
screen = pygame.display.set_mode((800, 400))
ID = ""
font = pygame.font.SysFont("Arial", 70)
while True:
    text = font.render("testtext", True, (255, 255, 255), (0, 0, 0))
    textRect = text.get_rect()
    textRect.center = (screen.get_width() // 2, screen.get_height() // 2)
    events = pygame.event.get()
    for event in events:
        if event.type == pygame.KEYDOWN:
            key = pygame.key.name(event.key)
            if key.isdigit():
                ID  = key
            elif key == "return":
                print(ID)
                ID = ""
            elif key == "left":
                pygame.quit()
                sys.exit()
    screen.fill((0, 0, 0))
    screen.blit(text, textRect)
    pygame.display.flip()

From testing it looks like there is about 3-4 miliseconds between each keystroke being sent by the scanner.

We've tried detecting keystrokes in a separate thread with different libraries, but have so far not found a workable solution.

CodePudding user response：

If I comment out the last three lines however (not updating the screen), the code is scanned successfully every time.

I would use an if statement to temporarily "comment out" these lines when input from the barcode scanner is received:

import sys, pygame
pygame.init()
screen = pygame.display.set_mode((800, 400))
ID = ""
font = pygame.font.SysFont("Arial", 70)
scanning = False
while True:
    text = font.render("testtext", True, (255, 255, 255), (0, 0, 0))
    textRect = text.get_rect()
    textRect.center = (screen.get_width() // 2, screen.get_height() // 2)
    events = pygame.event.get()
    for event in events:
        if event.type == pygame.KEYDOWN:
            key = pygame.key.name(event.key)
            if key.isdigit():
                scanning = True
                ID  = key
            elif key == "return":
                scanning = False
                print(ID)
                ID = ""
            elif key == "left":
                pygame.quit()
                sys.exit()
    if not scanning:
        screen.fill((0, 0, 0))
        screen.blit(text, textRect)
        pygame.display.flip()

As I don't have a barcode scanner, I'm unable to test this code. I have tested using keyboard input, but I have no idea of the time delay between my different keystrokes. All my tests were passed correctly

CodePudding user response：

Your main loop is notorious for not adding any delay between screen frame updates - this will make the screen updtae use 100% CPU - and it is likely the event engine is doing the equivalent of "frame skiping" when it finally has a chance to run.

Just add a pygame.time.delay(30) (pause 30 miliseconds) after the call to .display.flip() - that should give your O.S. a breath to catch up with the events. Since you said that commenting out any screen updates, it works, I am confident that given this space you should be fine.