How to move an image smoothly in pygame

Question

I have searched other related questions on stack overflow but can’t find the right solution.

Code Overview

basically I am trying to make a space invader game here at the bottom there is a space ship shooting down enemies and the enemies constantly move making the game hard and fun. while I am trying to make the enemies move, they paint lines which doesn’t look good.

Code

# importing modules
import pygame
import random

# initialize pygame
pygame.init()

# creating a window
screen = pygame.display.set_mode((800, 600))
# Title and Icon
pygame.display.set_caption("Space Shooters")
icon = pygame.image.load('spaceship.png')
pygame.display.set_icon(icon)

# Player
player = pygame.image.load('spaceship2.png')
playerX = 370
playerY = 500
playerX_change = 0

# Enemy
enemyImg = pygame.image.load('enemy.png')
enemyX = random.randint(6, 730)
enemyY = random.randint(45, 150)
enemyX_change = 0.3
enemyY_change = 0


# Defining and drawing spaceship
def spaceship(x, y):
    screen.blit(player, (x, y))


# Defining and drawing enemy
def enemy(x, y):
    screen.blit(enemyImg, (x, y))


# making the game window run endlessly and game loop
running = True

while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

        # Keystroke check (right, left)
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                playerX_change = -0.25
            if event.key == pygame.K_RIGHT:
                playerX_change = 0.25
        if event.type == pygame.KEYUP:
            if event.key == pygame.K_LEFT or event.key == pygame.K_RIGHT:
                playerX_change = 0

    # Changing X coordinates to move spaceship
    playerX += playerX_change

    if playerX <= 6:
        playerX = 6

    if playerX >= 730:
        playerX = 730

    enemyX += enemyX_change

    if enemyX <= 6:
        enemyX = 6
        enemyX_change = 0.3

    if enemyX >= 730:
        enemyX = 730
        enemyX_change = -0.3

    spaceship(playerX, playerY)

    enemy(enemyX, enemyY)
    # updating display
    pygame.display.update()

Expected Results vs Received Results

Expected Results: The enemy moves on the x axis at a constant speed and bounces back when a boundary has been hit. No trail should be formed.

Received Results: The enemy is moving as expected ,but painting a trail where it is and was going.

Asked By: Dev

||

Source

Answer 1

The display is redrawn in every frame, therefore the display must be cleared before drawing the objects in the scene:

while running:
    # [...]

    # clear the display 
    screen.fill(0)                 # <-- clear display

    # draw the scene
    spaceship(playerX, playerY)
    enemy(enemyX, enemyY)
    
    # update the display
    pygame.display.update()

The typical PyGame application loop has to:

limit the frames per second to limit CPU usage with pygame.time.Clock.tick
handle the events by calling either pygame.event.pump() or pygame.event.get().
update the game states and positions of objects dependent on the input events and time (respectively frames)
clear the entire display or draw the background
draw the entire scene (blit all the objects)
update the display by calling either pygame.display.update() or pygame.display.flip()

Answered By: Rabbid76

How to move an image smoothly in pygame

Question:

Code Overview

Code

Expected Results vs Received Results

Answers: