#! /usr/bin/env python3
#
def move_circle ( ):

  import pygame
#
#  Use "w", "s", "a", and "d" keys to move a red circle on the screen.
#  To stop, click on the "X" that closes the window.
#

#
#  Set up.
#
  pygame.init()
  screen = pygame.display.set_mode ( ( 1280, 720 ) )
  clock = pygame.time.Clock()
  running = True
  dt = 0

  player_pos = pygame.Vector2(screen.get_width() / 2, screen.get_height() / 2)
#
#  Game loop.'
#
  while running:
#
#  Exit the game if the user closed the game window.
#
    for event in pygame.event.get():
      if event.type == pygame.QUIT:
        running = False
#
#  Fill the screen with a color to wipe away anything from last frame
#
    screen.fill("purple")
#
#  Draw the circle.
#
    pygame.draw.circle ( screen, "red", player_pos, 40 )
#
#  Determine if a key was pressed.
#
    keys = pygame.key.get_pressed()
    if keys[pygame.K_w]:
      player_pos.y -= 300 * dt
    if keys[pygame.K_s]:
      player_pos.y += 300 * dt
    if keys[pygame.K_a]:
      player_pos.x -= 300 * dt
    if keys[pygame.K_d]:
      player_pos.x += 300 * dt
#
#  Display the updated screen.
#
    pygame.display.flip()
#
#  Set frames per second.
#
    fps = 60
#
#  Set dt, the frame rate.
#
    dt = clock.tick ( fps ) / 1000

  pygame.quit()

  return

if ( __name__ == "__main__" ):
  move_circle ( )