main.py

import pygame

pygame.init()
WIDTH, HEIGHT = 800, 600
screen = pygame.display.set_mode((WIDTH, HEIGHT))
pygame.display.set_caption("Pygame Drawing Interface")

WHITE = (255, 255, 255)
BLACK = (0, 0, 0)
BRUSH_WIDTH = 5

screen.fill(WHITE)
clock = pygame.time.Clock()

drawing = False
last_pos = None

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

        elif event.type == pygame.MOUSEBUTTONDOWN:
            if event.button == 1:
                screen.fill(WHITE)       # clear previous stroke
                drawing = True
                last_pos = event.pos     # starting point

        elif event.type == pygame.MOUSEBUTTONUP:
            if event.button == 1:
                drawing = False
                last_pos = None

    if drawing:
        mouse_pos = pygame.mouse.get_pos()
        if last_pos is not None:
            pygame.draw.line(screen, BLACK, last_pos, mouse_pos, BRUSH_WIDTH)
        last_pos = mouse_pos

    pygame.display.flip()
    clock.tick(60)

pygame.quit()