title: Cannot make sprite invisible in pygame
body: <p>So I'm making a basic pygame, and I have several "barriers" and "portals" on the game map.  The former are spots that the player cannot touch, and the latter are spots that change the level.</p>
  
  <p>I'm trying to make them invisible, so just have an invisible rectangle on the map that the collision detection would notice, but right now, when I blit it to the map, I have ugly black blobs.</p>
  
  <p>I tried using dirty rectangles, but that didn't seem to work out so well.</p>
  
  <p>My code (or at least the spots that handle the barriers and portals):</p>
  
  <pre><code>class Barrier(pygame.sprite.DirtySprite):
      '''class that builds up the invisible barriers in the game'''
  
      #constructor function
      def __init__(self, posX, posY, width, height): #create a self variable to refer to the object
      #call up the parent's constructor
          pygame.sprite.DirtySprite.__init__(self)
          self.dirty = 1
          self.visible = 0
  
          #Make the barrier.
          self.image = pygame.Surface([width, height])
  
          #debug code that makes sure that the barrier is in the right place
          #self.image.fill(white)
  
          # place the top left corner of the barrier at the given location
          self.rect = self.image.get_rect()
          self.rect.y = posY
          self.rect.x = posX
  
  barriers = pygame.sprite.Group() #global barrier list used in all maps
  portals = pygame.sprite.Group() #global portal list used in all maps
  
  
  class Portal(pygame.sprite.DirtySprite):
      '''class that builds up the portals in the game'''
  
      #constructor function
      def __init__(self, posX, posY, width, height): #create a self variable to refer to the object
      #call up the parent's constructor
          pygame.sprite.DirtySprite.__init__(self)
  
          self.dirty = 1
          self.visible = 0
  
          #Make the barrier.
          self.image = pygame.Surface([width, height])
  
          #debug code that makes sure that the barrier is in the right place
          self.image.fill(black)
  
          # place the top left corner of the barrier at the given location
          self.rect = self.image.get_rect()
          self.rect.y = posY
          self.rect.x = posX
  
  def LoadInside():
  
      barriers.empty()
      portals.empty()
      #Load up the level image
      whichLevel = 1
  
      background_image = pygame.image.load("House.png").convert()
  
      #a list of all the barriers in the room
      room_barrier_list = pygame.sprite.Group()
  
      #make a barrier out of all of the objects in the room
      barrierTopWall = Barrier(0,125,661,7)
      barrierLeftWall= Barrier(5, 130,5, 300)
      barrierBottomWallLeft= Barrier(10,414,292,7)
      barrierBottomWallRight= Barrier(364,412,298,7)
      barrierRightWall= Barrier(649,126,5, 294)
      bed = Barrier(19,199,62,93)
      smallTableChairs = Barrier(273,220,97,39)
      pot = Barrier(300,288,34,31)
      table = Barrier(493,242,151,42)
      chair1 = Barrier(459,255,28,35)
      chair2 = Barrier(490,296,31,28)
      chair3 = Barrier(553,293,31,28)
      chair4 = Barrier(621,292,31,28)
  
      #make a portal to get out
      door = Portal(300,413, 64,10)
  
  
      #add the barriers to the lists
      room_barrier_list.add(barrierTopWall, barrierLeftWall, barrierBottomWallLeft, barrierRightWall)
  
      barriers.add(room_barrier_list)
  
      all_sprites_list.add(barriers)
  
      room_barrier_list.add(smallTableChairs,pot,table,chair1,chair2,chair3,chair4, barrierBottomWallRight, bed)
      barriers.add(room_barrier_list)
      all_sprites_list.add(barriers)
  
      #add the portal to the list
      all_sprites_list.add(door)
  
      mainScreen.blit(background_image, [0,0])
  
  
  #
  # The above code handles the room barriers and portals
  #
  
  
  while done==False:
  
      for event in pygame.event.get(): #user did something
          if event.type == pygame.QUIT: #if the user hit the close button
                  done=True
  
                  # Move the player if an arrow key is pressed
          key = pygame.key.get_pressed()
          if key[pygame.K_LEFT]:
              faceWhatDirection = 'left' # set the faceWhatDirection variable
              player.updateLeft() # call up the animation function
              player.move(-10, 0)
  
          if key[pygame.K_RIGHT]:
              faceWhatDirection = 'right' # set the faceWhatDirection variable
              player.updateRight() # call up the animation function
              player.move(10, 0)
  
          if key[pygame.K_UP]:
              faceWhatDirection = 'up' # set the faceWhatDirection variable
              player.updateUp() # call up the animation function
              player.move(0, -10)
  
          if key[pygame.K_DOWN]:
              faceWhatDirection = 'down' # set the faceWhatDirection variable
              player.updateDown() # call up the animation function
              player.move(0, 10)
  
  
          #if the user presses the space bar, the attack button
          if key[pygame.K_SPACE]:
  
                  bullet = Bullet()
                  bullet_list.append(bullet) #adds bullet to the bullet list
                  all_sprites_list.add(bullet) #adds the bullet to the sprite list to be drawn
  
                  #puts the bullet in the same location as player (this needs to be changed to what direction player faces)
                  bullet.rect.x = player.rect.x
                  bullet.rect.y = player.rect.y + 15 # the + 15 places it at a location that is not on the player's face!
                  bullet.bulletDirection = faceWhatDirection
  
                  #checks to see what direction to move the bullet in
      for bullet in bullet_list:
          bullet.move_bullet()
  
          #see if the bullet hit anything
          barrier_hit_list = pygame.sprite.spritecollide(bullet, barriers, False)
  
          for barrier in barrier_hit_list:
          #remove the bullet if it hit something
              bullet_list.remove(bullet)
              all_sprites_list.remove(bullet)
  
      mainScreen.fill(black)#makes the background white, and thus, the white part of the images will be invisible
  
  
      if whichLevel == 1:
  
          LoadInside()
  
  
      else:
          LoadOutside()
  
  
      #draw the sprites
      all_sprites_list.draw(mainScreen)
  
  
  
      #limit the game to 20 fps
      clock.tick(20)
  
      #update the screen on the regular
      pygame.display.flip()
  
  pygame.quit()
  </code></pre>