import pygame

# Pygame setup


pygame.display.init()
# Optional -- get the MONITOR resolution...
video_info = pygame.display.Info()
win_width = video_info.current_w
win_height = video_info.current_h
is_fullscreen = False

# Create the (windowed) screen
screen = pygame.display.set_mode((800, 600))
running = True

# Create some variables
x = 400
y = 300
rad = 50
speed = 0.1

# GAME LOOP
while running:
    # INPUT-HANDLING
    # ... this is the heart of event-handling.  Does two things:
    #    a. gives us one event to handle (or not)
    #    b. saves the state of all input devices (mouse, keyboard, gamepads)
    evt = pygame.event.poll()
    # ... do some EVENT-HANDLING
    if evt.type == pygame.QUIT:
        # The user just clicked the close button
        running = False
    elif evt.type == pygame.KEYDOWN:
        # The user just pressed a keyboard button.
        if evt.key == pygame.K_F5:
            if is_fullscreen:
                screen = pygame.display.set_mode((800, 600))
                is_fullscreen = False
            else:
                screen = pygame.display.set_mode((win_width, win_height), pygame.FULLSCREEN)
                is_fullscreen = True
        elif evt.key == pygame.K_LSHIFT or evt.key == pygame.K_RSHIFT:
            speed = 1
    elif evt.type == pygame.KEYUP:
        if evt.key == pygame.K_LSHIFT or evt.key == pygame.K_RSHIFT:
            speed = 0.1
    # ... do some DEVICE-POLLING
    pressed_keys = pygame.key.get_pressed()
    #    ... the full list of keys can be found at: http://pygame.org/docs/ref/key.html
    if pressed_keys[pygame.K_ESCAPE]:
        running = False
    if pressed_keys[pygame.K_a] or pressed_keys[pygame.K_LEFT]:
        x -= speed            # Hmmmm...
    if pressed_keys[pygame.K_d] or pressed_keys[pygame.K_RIGHT]:
        x += speed            # Hmmmm...

    # UPDATE-VARIABLES
    if x < rad:
        x = rad
    if x > screen.get_width() - rad:
        x = screen.get_width() - rad

    # DRAWING
    screen.fill((0, 0, 0))
    pygame.draw.circle(screen, (255,0,0), (int(x), y), rad)
    pygame.display.flip()

# Pygame shutdown
pygame.display.quit()