Why Does My PyGame Ball Stretch Instead of Move?

Ball Movement in PyGame

When building a game using PyGame, you often encounter the problem of how to move objects on the screen. While building a table tennis game, the author tried to move the ball but ran into some problems. When the move_right method is called, the ball does not move to the right, but extends to the right.

The root of the problem

The root of this problem lies in the drawing mechanism of PyGame. In each frame, PyGame draws all objects onto the display surface. Therefore, if the previous frame is not cleared, the newly drawn object will be superimposed on the old object, causing a trailing effect.

Workaround

To solve this problem, the display surface needs to be cleared at the beginning of each frame. The code can be modified like this:

while True:
    # [...]

    screen.fill(0) # <--- 清除显示表面

    main.draw_elements()
    main.move_ball()
    main.ball.x_pos += main.ball.speed
    pygame.display.flip()

    # [...]

By clearing the display surface at the beginning of each frame, you can remove the trailing effect and allow the ball to move correctly instead of leaving a trail.

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