What causes lag in the game?

Question

I made a very simple game in python with pygame, and I don't know why it is lagging, can somebody help me?

I tried to fix it myself, but I couldn't and I couldn't find a way to fix it online.

And it is not because of my PC, it has 16 gigabytes of RAM, SSD 512 GB of storage, processor: Intel Core i7-7600U 2.90 GHz.

This is the code:

import pygame

pygame.init()

win = pygame.display.set_mode((500, 500))

pygame.display.set_caption("Platformer")

colour = (255, 0, 0) # Colour red
x = 50
y = 50
width = 40
height = 60
vel = 5

isJump = False
jumpCount = 10

run = True

while run:
    pygame.time.delay(100)

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

    keys = pygame.key.get_pressed()

    if keys[pygame.K_LEFT] and x > vel:
        x = x - vel

    if keys[pygame.K_RIGHT] and x < 500 - width - vel:
        x = x + vel

    if not(isJump):

        if keys[pygame.K_UP] and y > vel:
            y = y - vel

        if keys[pygame.K_DOWN] and y < 500 - height - vel:
            y = y + vel

        if keys[pygame.K_SPACE]:
            isJump = True

    else:
        if jumpCount >= -10:
            neg = 1
            if jumpCount < 0:
                neg = -1
            y = y - (jumpCount ** 2) * 0.5 * neg
            jumpCount = jumpCount - 1
            
        else:
            isJump = False
            jumpCount = 10
            

    win.fill((0, 0, 0))
    pygame.draw.rect(win, colour, (x, y, width, height))
    pygame.display.update()
    

pygame.quit()

Answer 1

The application lags, because of the large delay in the application loop. Remove the delay:

pygame.time.delay(100)

---

Use pygame.time.Clock to control the frames per second and thus the game speed.

The method tick() of a pygame.time.Clock object, delays the game in that way, that every iteration of the loop consumes the same period of time. See pygame.time.Clock.tick():

This method should be called once per frame.

That means that the loop:

clock = pygame.time.Clock()
run = True
while run:
   clock.tick(60)

runs 60 times per second.

---

Complete example:

import pygame

pygame.init()
win = pygame.display.set_mode((500, 500))
pygame.display.set_caption("Platformer")

colour = (255, 0, 0) # Colour red
x = 50
y = 50
width = 40
height = 60
vel = 5

isJump = False
jumpCount = 10

clock = pygame.time.Clock()
run = True
while run:
    clock.tick(60)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

    keys = pygame.key.get_pressed()
    if keys[pygame.K_LEFT] and x > vel:
        x = x - vel
    if keys[pygame.K_RIGHT] and x < 500 - width - vel:
        x = x + vel

    if not(isJump):
        if keys[pygame.K_UP] and y > vel:
            y = y - vel
        if keys[pygame.K_DOWN] and y < 500 - height - vel:
            y = y + vel
        if keys[pygame.K_SPACE]:
            isJump = True

    else:
        if jumpCount >= -10:
            neg = 1
            if jumpCount < 0:
                neg = -1
            y = y - (jumpCount ** 2) * 0.5 * neg
            jumpCount = jumpCount - 1
            
        else:
            isJump = False
            jumpCount = 10
            

    win.fill((0, 0, 0))
    pygame.draw.rect(win, colour, (x, y, width, height))
    pygame.display.update()

pygame.quit()