Why do circles only display when I click but are still affected by physics as soon as the code loads?

Question

I am trying to spawn circles when I click on the screen but the circles only display when I click even though they are being affected as soon as I run the code and it is only grabbing my initial mouse position. I am using pygame, pygame.locals and sys libraries.

code:

pygame.init()

screen = pygame.display.set_mode((1000, 500))
green = (0, 255, 0)

mx, my = pygame.mouse.get_pos()
circle_pos = [mx, my]

circle = False

clock = pygame.time.Clock()
while True:
    screen.fill((15, 15, 15))

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()

    if circle == True:
        pygame.draw.circle(screen, green, circle_pos, 5)

    if event.type == pygame.MOUSEBUTTONDOWN:
        circle = True

    circle_pos[1] += 1

    if circle_pos[1] > 495:
        boundaries = circle_pos[1] - 495
        circle_pos[1] -= boundaries

    pygame.display.update()
    clock.tick(120)
    print(clock.get_fps())

pygame.quit()

Answer 1

If you want to draw objects permanently, you must draw them every frame in the application loop.

You have to add a list for the circle positions:

circles = []

Add a new position to the list when the mouse button is clicked:

while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()

        if event.type == pygame.MOUSEBUTTONDOWN:
            circles.append(list(event.pos))

    # [...]

Draw all the circles in the list in the application loop:

while True:
    # [...]

    screen.fill((15, 15, 15))

    for circle_pos in circles:
        pygame.draw.circle(screen, green, circle_pos, 5)

    pygame.draw.circle(screen, green, pygame.mouse.get_pos(), 5)

    pygame.display.update()
    clock.tick(120)

---

Complete example:

import pygame
pygame.init()

screen = pygame.display.set_mode((1000, 500))
clock = pygame.time.Clock()
green = (0, 255, 0)
circles = []

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

        if event.type == pygame.MOUSEBUTTONDOWN:
            circles.append(list(event.pos))

    screen.fill((15, 15, 15))
    for circle_pos in circles:
        pygame.draw.circle(screen, green, circle_pos, 5)
    pygame.draw.circle(screen, green, pygame.mouse.get_pos(), 5)
    pygame.display.update()
    clock.tick(120)

pygame.quit()
sys.exit()

---

Change the positions contained in the list to move the circles:

import pygame
pygame.init()

screen = pygame.display.set_mode((1000, 500))
clock = pygame.time.Clock()
green = (0, 255, 0)
circles = []

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

        if event.type == pygame.MOUSEBUTTONDOWN:
            circles.append(list(event.pos))

    screen.fill((15, 15, 15))
    mouse_pos = pygame.mouse.get_pos()
    for circle_pos in circles:
        dx = mouse_pos[0] - circle_pos[0] 
        dy = mouse_pos[1] - circle_pos[1]
        if abs(dx) > abs(dy):  
            circle_pos[0] += 1 if dx > 0 else -1
        elif dy != 0:
            circle_pos[1] += 1 if dy > 0 else -1
        pygame.draw.circle(screen, green, circle_pos, 5)
    pygame.draw.circle(screen, green, pygame.mouse.get_pos(), 5)
    pygame.display.update()
    clock.tick(120)

pygame.quit()
sys.exit()