Why Is My Pygame Application Loop Not Working Properly?

Troubleshooting a Faulty Pygame Application Loop

Issue: Application loop not functioning correctly.

Context:

The provided Python script attempts to create a basic 2D adventure game using Pygame, but the application loop seems to be malfunctioning. The user is seeking guidance in implementing a camera system within the game. However, the primary focus of this response will be on resolving the faulty application loop.

Root Cause:

The incorrect approach in the script lies in attempting to draw the background at the position of an object, followed by moving the object and blitting it on its new position. This approach is redundant and unnecessary.

Resolution:

A fundamental understanding of the main application loop is crucial:

1. Event Handling: Handle events using either pygame.event.pump() or pygame.event.get().
2. Object Updates: Update game states and object positions based on input events and time (frames).
3. Background Rendering: Clear the entire display or draw the background.
4. Scene Rendering: Draw the entire scene (blit all objects).
5. Display Update: Update the display using either pygame.display.update() or pygame.display.flip().

In summary, the application loop should proceed as follows:

• Handle events
• Update objects (based on input and frames)
• Draw background
• Draw scene
• Update display

Modified Code:

while 1:

    # Event handling
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit()

    # Object updates
    keys = pygame.key.get_pressed()
    if keys[pygame.K_LEFT]:
        objects[0].move_left()    
    if keys[pygame.K_RIGHT]:
        objects[0].move_right()
    if keys[pygame.K_UP]:
        objects[0].move_up()
    if keys[pygame.K_DOWN]:
        objects[0].move_down()

    for num in range(num_objects - 1):
        objects[num + 1].rand_move()

    # Background rendering
    screen.blit(background, (0, 0))

    # Scene rendering
    for o in objects:
        screen.blit(o.image, o.pos)

    # Display update
    pygame.display.update()
    pygame.time.delay(100)

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