text: ##    pygame - Python Game Library
  ##    Copyright (C) 2000-2003, 2007  Pete Shinners
  ##              (C) 2004 Joe Wreschnig
  ##    This library is free software; you can redistribute it and/or
  ##    modify it under the terms of the GNU Library General Public
  ##    License as published by the Free Software Foundation; either
  ##    version 2 of the License, or (at your option) any later version.
  ##
  ##    This library is distributed in the hope that it will be useful,
  ##    but WITHOUT ANY WARRANTY; without even the implied warranty of
  ##    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  ##    Library General Public License for more details.
  ##
  ##    You should have received a copy of the GNU Library General Public
  ##    License along with this library; if not, write to the Free
  ##    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
  ##    MA  02110-1301  USA
  ##
  ##    Pete Shinners
  ##    pete@shinners.org
  
  """pygame module with basic game object classes
  This module contains several simple classes to be used within games. There
  is the main Sprite class and several Group classes that contain Sprites.
  The use of these classes is entirely optional when using Pygame. The classes
  are fairly lightweight and only provide a starting place for the code
  that is common to most games.
  The Sprite class is intended to be used as a base class for the different
  types of objects in the game. There is also a base Group class that simply
  stores sprites. A game could create new types of Group classes that operate
  on specially customized Sprite instances they contain.
  The basic Sprite class can draw the Sprites it contains to a Surface. The
  Group.draw() method requires that each Sprite have a Surface.image attribute
  and a Surface.rect. The Group.clear() method requires these same attributes,
  and can be used to erase all the Sprites with background. There are also
  more advanced Groups: pygame.sprite.RenderUpdates() and
  pygame.sprite.OrderedUpdates().
  Lastly, this module contains several collision functions. These help find
  sprites inside multiple groups that have intersecting bounding rectangles.
  To find the collisions, the Sprites are required to have a Surface.rect
  attribute assigned.
  The groups are designed for high efficiency in removing and adding Sprites
  to them. They also allow cheap testing to see if a Sprite already exists in
  a Group. A given Sprite can exist in any number of groups. A game could use
  some groups to control object rendering, and a completely separate set of
  groups to control interaction or player movement. Instead of adding type
  attributes or bools to a derived Sprite class, consider keeping the
  Sprites inside organized Groups. This will allow for easier lookup later
  in the game.
  Sprites and Groups manage their relationships with the add() and remove()
  methods. These methods can accept a single or multiple targets for
  membership.  The default initializers for these classes also takes a
  single or list of targets for initial membership. It is safe to repeatedly
  add and remove the same Sprite from a Group.
  While it is possible to design sprite and group classes that don't derive
  from the Sprite and AbstractGroup classes below, it is strongly recommended
  that you extend those when you add a Sprite or Group class.
  Sprites are not thread safe.  So lock them yourself if using threads.
  """
  
  ##todo
  ## a group that holds only the 'n' most recent elements.
  ## sort of like the GroupSingle class, but holding more
  ## than one sprite
  ##
  ## drawing groups that can 'automatically' store the area
  ## underneath, so the can "clear" without needing a background
  ## function. obviously a little slower than normal, but nice
  ## to use in many situations. (also remember it must "clear"
  ## in the reverse order that it draws :])
  ##
  ## the drawing groups should also be able to take a background
  ## function, instead of just a background surface. the function
  ## would take a surface and a rectangle on that surface to erase.
  ##
  ## perhaps more types of collision functions? the current two
  ## should handle just about every need, but perhaps more optimized
  ## specific ones that aren't quite so general but fit into common
  ## specialized cases.
  
  import gsdl2
  from gsdl2 import Rect
  from gsdl2._time import get_ticks
  
  
  class Sprite(object):
      """simple base class for visible game objects
      pygame.sprite.Sprite(*groups): return Sprite
      The base class for visible game objects. Derived classes will want to
      override the Sprite.update() and assign a Sprite.image and
      Sprite.rect attributes.  The initializer can accept any number of
      Group instances to be added to.
      When subclassing the Sprite, be sure to call the base initializer before
      adding the Sprite to Groups.
      """
  
      def __init__(self, *groups):
          self.__g = {}  # The groups the sprite is in
          if groups: self.add(groups)
  
      def add(self, *groups):
          """add the sprite to groups
          Sprite.add(*groups): return None
          Any number of Group instances can be passed as arguments. The
          Sprite will be added to the Groups it is not already a member of.
          """
          has = self.__g.__contains__
          for group in groups:
              if hasattr(group, '_spritegroup'):
                  if not has(group):
                      group.add_internal(self)
                      self.add_internal(group)
              else:
                  self.add(*group)
  
      def remove(self, *groups):
          """remove the sprite from groups
          Sprite.remove(*groups): return None
          Any number of Group instances can be passed as arguments. The Sprite will
          be removed from the Groups it is currently a member of.
          """
          has = self.__g.__contains__
          for group in groups:
              if hasattr(group, '_spritegroup'):
                  if has(group):
                      group.remove_internal(self)
                      self.remove_internal(group)
              else:
                  self.remove(*group)
  
      def add_internal(self, group):
          self.__g[group] = 0
  
      def remove_internal(self, group):
          del self.__g[group]
  
      def update(self, *args):
          """method to control sprite behavior
          Sprite.update(*args):
          The default implementation of this method does nothing; it's just a
          convenient "hook" that you can override. This method is called by
          Group.update() with whatever arguments you give it.
          There is no need to use this method if not using the convenience
          method by the same name in the Group class.
          """
          pass
  
      def kill(self):
          """remove the Sprite from all Groups
          Sprite.kill(): return None
          The Sprite is removed from all the Groups that contain it. This won't
          change anything about the state of the Sprite. It is possible to continue
          to use the Sprite after this method has been called, including adding it
          to Groups.
          """
          for c in self.__g.keys():
              c.remove_internal(self)
          self.__g.clear()
  
      def groups(self):
          """list of Groups that contain this Sprite
          Sprite.groups(): return group_list
          Return a list of all the Groups that contain this Sprite.
          """
          return self.__g.keys()
  
      def alive(self):
          """does the sprite belong to any groups
          Sprite.alive(): return bool
          Returns True when the Sprite belongs to one or more Groups.
          """
          return (len(self.__g) != 0)
  
      def __repr__(self):
          return "<%s sprite(in %d groups)>" % (self.__class__.__name__, len(self.__g))
  
  
  class DirtySprite(Sprite):
      """a more featureful subclass of Sprite with more attributes
      pygame.sprite.DirtySprite(*groups): return DirtySprite
      Extra DirtySprite attributes with their default values:
      dirty = 1
          if set to 1, it is repainted and then set to 0 again
          if set to 2 then it is always dirty ( repainted each frame,
          flag is not reset)
          0 means that it is not dirty and therefor not repainted again
      blendmode = 0
          its the special_flags argument of blit, blendmodes
      source_rect = None
          source rect to use, remember that it is relative to
          topleft (0,0) of self.image
      visible = 1
          normally 1, if set to 0 it will not be repainted
          (you must set it dirty too to be erased from screen)
      layer = 0
          (READONLY value, it is read when adding it to the
          LayeredUpdates, for details see doc of LayeredUpdates)
      """
  
      def __init__(self, *groups):
          self.dirty = 1
          self.blendmode = 0  # pygame 1.8, reffered as special_flags in
          # the documentation of blit
          self._visible = 1
          self._layer = 0  # READ ONLY by LayeredUpdates or LayeredDirty
          self.source_rect = None
          Sprite.__init__(self, *groups)
  
      def _set_visible(self, val):
          """set the visible value (0 or 1) and makes the sprite dirty"""
          self._visible = val
          if self.dirty < 2:
              self.dirty = 1
  
      def _get_visible(self):
          """returns the visible value of that sprite"""
          return self._visible
  
      visible = property(lambda self: self._get_visible(), \
                         lambda self, value: self._set_visible(value), \
                         doc="you can make this sprite disappear without removing it from the group,\n" +
                             "values 0 for invisible and 1 for visible")
  
      def __repr__(self):
          return "<%s DirtySprite(in %d groups)>" % (self.__class__.__name__, len(self.groups()))
  
  
  class AbstractGroup(object):
      """A base for containers for sprites. It does everything
         needed to behave as a normal group. You can easily inherit
         a new group class from this, or the other groups below,
         if you want to add more features.
         Any AbstractGroup-derived sprite groups act like sequences,
         and support iteration, len, and so on."""
  
      # dummy val to identify sprite groups, and avoid infinite recursion.
      _spritegroup = True
  
      def __init__(self):
          self.spritedict = {}
          self.lostsprites = []
  
      def sprites(self):
          """sprites()
             get a list of sprites in the group
             Returns an object that can be looped over with a 'for' loop.
             (For now it is always a list, but newer version of Python
             could return different iterators.) You can also iterate directly
             over the sprite group."""
          return list(self.spritedict.keys())
  
      def add_internal(self, sprite):
          self.spritedict[sprite] = 0
  
      def remove_internal(self, sprite):
          r = self.spritedict[sprite]
          if r is not 0:
              self.lostsprites.append(r)
          del (self.spritedict[sprite])
  
      def has_internal(self, sprite):
          return sprite in self.spritedict
  
      def copy(self):
          """copy()
             copy a group with all the same sprites
             Returns a copy of the group that is the same class
             type, and has the same sprites in it."""
          return self.__class__(self.sprites())
  
      def __iter__(self):
          return iter(self.sprites())
  
      def __contains__(self, sprite):
          return self.has(sprite)
  
      def add(self, *sprites):
          """add(sprite, list, or group, ...)
             add sprite to group
             Add a sprite or sequence of sprites to a group."""
          for sprite in sprites:
              # It's possible that some sprite is also an iterator.
              # If this is the case, we should add the sprite itself,
              # and not the objects it iterates over.
              if isinstance(sprite, Sprite):
                  if not self.has_internal(sprite):
                      self.add_internal(sprite)
                      sprite.add_internal(self)
              else:
                  try:
                      # See if sprite is an iterator, like a list or sprite
                      # group.
                      for spr in sprite:
                          self.add(spr)
                  except (TypeError, AttributeError):
                      # Not iterable, this is probably a sprite that happens
                      # to not subclass Sprite. Alternately, it could be an
                      # old-style sprite group.
                      if hasattr(sprite, '_spritegroup'):
                          for spr in sprite.sprites():
                              if not self.has_internal(spr):
                                  self.add_internal(spr)
                                  spr.add_internal(self)
                      elif not self.has_internal(sprite):
                          self.add_internal(sprite)
                          sprite.add_internal(self)
  
      def remove(self, *sprites):
          """remove(sprite, list, or group, ...)
             remove sprite from group
             Remove a sprite or sequence of sprites from a group."""
          # This function behaves essentially the same as Group.add.
          # Check for Spritehood, check for iterability, check for
          # old-style sprite group, and fall back to assuming
          # spritehood.
          for sprite in sprites:
              if isinstance(sprite, Sprite):
                  if self.has_internal(sprite):
                      self.remove_internal(sprite)
                      sprite.remove_internal(self)
              else:
                  try:
                      for spr in sprite: self.remove(spr)
                  except (TypeError, AttributeError):
                      if hasattr(sprite, '_spritegroup'):
                          for spr in sprite.sprites():
                              if self.has_internal(spr):
                                  self.remove_internal(spr)
                                  spr.remove_internal(self)
                      elif self.has_internal(sprite):
                          self.remove_internal(sprite)
                          sprite.remove_internal(self)
  
      def has(self, *sprites):
          """has(sprite or group, ...)
             ask if group has a sprite or sprites
             Returns true if the given sprite or sprites are
             contained in the group. You can also use 'sprite in group'
             or 'subgroup in group'."""
          # Again, this follows the basic pattern of Group.add and
          # Group.remove.
          for sprite in sprites:
              if isinstance(sprite, Sprite):
                  return self.has_internal(sprite)
  
              try:
                  for spr in sprite:
                      if not self.has(spr):
                          return False
                  return True
              except (TypeError, AttributeError):
                  if hasattr(sprite, '_spritegroup'):
                      for spr in sprite.sprites():
                          if not self.has_internal(spr):
                              return False
                      return True
                  else:
                      return self.has_internal(sprite)
  
      def update(self, *args):
          """update(*args)
             call update for all member sprites
             calls the update method for all sprites in the group.
             Passes all arguments on to the Sprite update function."""
          for s in self.sprites(): s.update(*args)
  
      def draw(self, surface):
          """draw(surface)
             draw all sprites onto the surface
             Draws all the sprites onto the given surface."""
          sprites = self.sprites()
          surface_blit = surface.blit
          for spr in sprites:
              self.spritedict[spr] = surface_blit(spr.image, spr.rect)
          self.lostsprites = []
  
      def clear(self, surface, bgd):
          """clear(surface, bgd)
             erase the previous position of all sprites
             Clears the area of all drawn sprites. the bgd
             argument should be Surface which is the same
             dimensions as the surface. The bgd can also be
             a function which gets called with the passed
             surface and the area to be cleared."""
          try:
              bgd.__call__
          except AttributeError:
              pass
          else:
              for r in self.lostsprites:
                  bgd(surface, r)
              for r in self.spritedict.values():
                  if r is not 0: bgd(surface, r)
              return
          surface_blit = surface.blit
          for r in self.lostsprites:
              surface_blit(bgd, r, r)
          for r in self.spritedict.values():
              if r is not 0: surface_blit(bgd, r, r)
  
      def empty(self):
          """empty()
             remove all sprites
             Removes all the sprites from the group."""
          for s in self.sprites():
              self.remove_internal(s)
              s.remove_internal(self)
  
      def __nonzero__(self):
          return (len(self.sprites()) != 0)
  
      def __len__(self):
          """len(group)
             number of sprites in group
             Returns the number of sprites contained in the group."""
          return len(self.sprites())
  
      def __repr__(self):
          return "<%s(%d sprites)>" % (self.__class__.__name__, len(self))
  
  
  class Group(AbstractGroup):
      """container class for many Sprites
      pygame.sprite.Group(*sprites): return Group
      A simple container for Sprite objects. This class can be inherited to
      create containers with more specific behaviors. The constructor takes any
      number of Sprite arguments to add to the Group. The group supports the
      following standard Python operations:
          in      test if a Sprite is contained
          len     the number of Sprites contained
          bool test if any Sprites are contained
          iter    iterate through all the Sprites
      The Sprites in the Group are not ordered, so drawing and iterating the
      Sprites is in no particular order.
      """
  
      def __init__(self, *sprites):
          AbstractGroup.__init__(self)
          self.add(*sprites)
  
  
  RenderPlain = Group
  RenderClear = Group
  
  
  class RenderUpdates(Group):
      """Group class that tracks dirty updates
      pygame.sprite.RenderUpdates(*sprites): return RenderUpdates
      This class is derived from pygame.sprite.Group(). It has an extended draw()
      method that tracks the changed areas of the screen.
      """
  
      def draw(self, surface):
          spritedict = self.spritedict
          surface_blit = surface.blit
          dirty = self.lostsprites
          self.lostsprites = []
          dirty_append = dirty.append
          for s in self.sprites():
              r = spritedict[s]
              newrect = surface_blit(s.image, s.rect)
              if r is 0:
                  dirty_append(newrect)
              else:
                  if newrect.colliderect(r):
                      newrect.union_ip(r)
                      dirty_append(newrect)
                  else:
                      dirty_append(newrect)
                      dirty_append(r)
              spritedict[s] = newrect
          return dirty
  
  
  class OrderedUpdates(RenderUpdates):
      """RenderUpdates class that draws Sprites in order of addition
      pygame.sprite.OrderedUpdates(*spites): return OrderedUpdates
      This class derives from pygame.sprite.RenderUpdates().  It maintains
      the order in which the Sprites were added to the Group for rendering.
      This makes adding and removing Sprites from the Group a little
      slower than regular Groups.
      """
  
      def __init__(self, *sprites):
          self._spritelist = []
          RenderUpdates.__init__(self, *sprites)
  
      def sprites(self):
          return list(self._spritelist)
  
      def add_internal(self, sprite):
          RenderUpdates.add_internal(self, sprite)
          self._spritelist.append(sprite)
  
      def remove_internal(self, sprite):
          RenderUpdates.remove_internal(self, sprite)
          self._spritelist.remove(sprite)
  
  
  class LayeredUpdates(AbstractGroup):
      """LayeredUpdates Group handles layers, that draws like OrderedUpdates.
      pygame.sprite.LayeredUpdates(*spites, **kwargs): return LayeredUpdates
  
      This group is fully compatible with pygame.sprite.Sprite.
      New in pygame 1.8.0
      """
  
      def __init__(self, *sprites, **kwargs):
          """
          You can set the default layer through kwargs using 'default_layer'
          and an integer for the layer. The default layer is 0.
  
          If the sprite you add has an attribute layer then that layer will
          be used.
          If the **kwarg contains 'layer' then the sprites passed will be
          added to that layer (overriding the sprite.layer attribute).
          If neither sprite has attribute layer nor kwarg then the default
          layer is used to add the sprites.
          """
          self._spritelayers = {}
          self._spritelist = []
          AbstractGroup.__init__(self)
          self._default_layer = kwargs.get('default_layer', 0)
  
          self.add(*sprites, **kwargs)
  
      def add_internal(self, sprite, layer=None):
          """
          Do not use this method directly. It is used by the group to add a
          sprite internally.
          """
          self.spritedict[sprite] = Rect(0, 0, 0, 0)  # add a old rect
  
          if layer is None:
              try:
                  layer = sprite._layer
              except AttributeError:
                  layer = self._default_layer
  
          self._spritelayers[sprite] = layer
          if hasattr(sprite, '_layer'):
              sprite._layer = layer
  
          # add the sprite at the right position
          # bisect algorithmus
          sprites = self._spritelist  # speedup
          sprites_layers = self._spritelayers
          leng = len(sprites)
          low = 0
          high = leng - 1
          mid = low
          while (low <= high):
              mid = low + (high - low) // 2
              if (sprites_layers[sprites[mid]] <= layer):
                  low = mid + 1
              else:
                  high = mid - 1
          # linear search to find final position
          while (mid < leng and sprites_layers[sprites[mid]] <= layer):
              mid += 1
          sprites.insert(mid, sprite)
  
      def add(self, *sprites, **kwargs):
          """add a sprite or sequence of sprites to a group
          LayeredUpdates.add(*sprites, **kwargs): return None
          If the sprite(s) have an attribute layer then that is used
          for the layer. If kwargs contains 'layer' then the sprite(s)
          will be added to that argument (overriding the sprite layer
          attribute). If neither is passed then the sprite(s) will be
          added to the default layer.
          """
          layer = None
          if 'layer' in kwargs:
              layer = kwargs['layer']
          if sprites is None or not sprites:
              return
          for sprite in sprites:
              # It's possible that some sprite is also an iterator.
              # If this is the case, we should add the sprite itself,
              # and not the objects it iterates over.
              if isinstance(sprite, Sprite):
                  if not self.has_internal(sprite):
                      self.add_internal(sprite, layer)
                      sprite.add_internal(self)
              else:
                  try:
                      # See if sprite is an iterator, like a list or sprite
                      # group.
                      for spr in sprite:
                          self.add(spr, **kwargs)
                  except (TypeError, AttributeError):
                      # Not iterable, this is probably a sprite that happens
                      # to not subclass Sprite. Alternately, it could be an
                      # old-style sprite group.
                      if hasattr(sprite, '_spritegroup'):
                          for spr in sprite.sprites():
                              if not self.has_internal(spr):
                                  self.add_internal(spr, layer)
                                  spr.add_internal(self)
                      elif not self.has_internal(sprite):
                          self.add_internal(sprite, layer)
                          sprite.add_internal(self)
  
      def remove_internal(self, sprite):
          """
          Do not use this method directly. It is used by the group to
          add a sprite.
          """
          self._spritelist.remove(sprite)
          # these dirty rects are suboptimal for one frame
          self.lostsprites.append(self.spritedict[sprite])  # dirty rect
          if hasattr(sprite, 'rect'):
              self.lostsprites.append(sprite.rect)  # dirty rect
  
          self.spritedict.pop(sprite, 0)
          self._spritelayers.pop(sprite)
  
      def sprites(self):
          """returns a ordered list of sprites (first back, last top).
          LayeredUpdates.sprites(): return sprites
          """
          return list(self._spritelist)
  
      def draw(self, surface):
          """draw all sprites in the right order onto the passed surface.
          LayeredUpdates.draw(surface): return Rect_list
          """
          spritedict = self.spritedict
          surface_blit = surface.blit
          dirty = self.lostsprites
          self.lostsprites = []
          dirty_append = dirty.append
          for spr in self.sprites():
              rec = spritedict[spr]
              newrect = surface_blit(spr.image, spr.rect)
              if rec is 0:
                  dirty_append(newrect)
              else:
                  if newrect.colliderect(rec):
                      dirty_append(newrect.union(rec))
                  else:
                      dirty_append(newrect)
                      dirty_append(rec)
              spritedict[spr] = newrect
          return dirty
  
      def get_sprites_at(self, pos):
          """returns a list with all sprites at that position.
          LayeredUpdates.get_sprites_at(pos): return colliding_sprites
          Bottom sprites first, top last.
          """
          _sprites = self._spritelist
          rect = Rect(pos, (0, 0))
          colliding_idx = rect.collidelistall(_sprites)
          colliding = []
          colliding_append = colliding.append
          for i in colliding_idx:
              colliding_append(_sprites[i])
          return colliding
  
      def get_sprite(self, idx):
          """returns the sprite at the index idx from the groups sprites
          LayeredUpdates.get_sprite(idx): return sprite
          Raises IndexOutOfBounds if the idx is not within range.
          """
          return self._spritelist[idx]
  
      def remove_sprites_of_layer(self, layer_nr):
          """removes all sprites from a layer and returns them as a list
          LayeredUpdates.remove_sprites_of_layer(layer_nr): return sprites
          """
          sprites = self.get_sprites_from_layer(layer_nr)
          self.remove(sprites)
          return sprites
  
      # ---# layer methods
      def layers(self):
          """returns a list of layers defined (unique), sorted from botton up.
          LayeredUpdates.layers(): return layers
          """
          layers = set()
          for layer in self._spritelayers.values():
              layers.add(layer)
          return list(layers)
  
      def change_layer(self, sprite, new_layer):
          """changes the layer of the sprite
          LayeredUpdates.change_layer(sprite, new_layer): return None
          sprite must have been added to the renderer. It is not checked.
          """
          sprites = self._spritelist  # speedup
          sprites_layers = self._spritelayers  # speedup
  
          sprites.remove(sprite)
          sprites_layers.pop(sprite)
  
          # add the sprite at the right position
          # bisect algorithmus
          leng = len(sprites)
          low = 0
          high = leng - 1
          mid = low
          while (low <= high):
              mid = low + (high - low) // 2
              if (sprites_layers[sprites[mid]] <= new_layer):
                  low = mid + 1
              else:
                  high = mid - 1
          # linear search to find final position
          while (mid < leng and sprites_layers[sprites[mid]] <= new_layer):
              mid += 1
          sprites.insert(mid, sprite)
          if hasattr(sprite, 'layer'):
              sprite.layer = new_layer
  
          # add layer info
          sprites_layers[sprite] = new_layer
  
      def get_layer_of_sprite(self, sprite):
          """
          Returns the layer that sprite is currently in. If the sprite is not
          found then it will return the default layer.
          """
          return self._spritelayers.get(sprite, self._default_layer)
  
      def get_top_layer(self):
          """returns the top layer
          LayeredUpdates.get_top_layer(): return layer
          """
          return self._spritelayers[self._spritelist[-1]]
  
      def get_bottom_layer(self):
          """returns the bottom layer
          LayeredUpdates.get_bottom_layer(): return layer
          """
          return self._spritelayers[self._spritelist[0]]
  
      def move_to_front(self, sprite):
          """brings the sprite to front layer
          LayeredUpdates.move_to_front(sprite): return None
          Brings the sprite to front, changing sprite layer to topmost layer
          (added at the end of that layer).
          """
          self.change_layer(sprite, self.get_top_layer())
  
      def move_to_back(self, sprite):
          """moves the sprite to the bottom layer
          LayeredUpdates.move_to_back(sprite): return None
          Moves the sprite to the bottom layer, moving it behind
          all other layers and adding one additional layer.
          """
          self.change_layer(sprite, self.get_bottom_layer() - 1)
  
      def get_top_sprite(self):
          """returns the topmost sprite
          LayeredUpdates.get_top_sprite(): return Sprite
          """
          return self._spritelist[-1]
  
      def get_sprites_from_layer(self, layer):
          """returns all sprites from a layer, ordered by how they where added
          LayeredUpdates.get_sprites_from_layer(layer): return sprites
          Returns all sprites from a layer, ordered by how they where added.
          It uses linear search and the sprites are not removed from layer.
          """
          sprites = []
          sprites_append = sprites.append
          sprite_layers = self._spritelayers
          for spr in self._spritelist:
              if sprite_layers[spr] == layer:
                  sprites_append(spr)
              elif sprite_layers[spr] > layer:  # break after because no other will
                  # follow with same layer
                  break
          return sprites
  
      def switch_layer(self, layer1_nr, layer2_nr):
          """switches the sprites from layer1 to layer2
          LayeredUpdates.switch_layer(layer1_nr, layer2_nr): return None
          The layers number must exist, it is not checked.
          """
          sprites1 = self.remove_sprites_of_layer(layer1_nr)
          for spr in self.get_sprites_from_layer(layer2_nr):
              self.change_layer(spr, layer1_nr)
          self.add(sprites1, layer=layer2_nr)
  
  
  class LayeredDirty(LayeredUpdates):
      """LayeredDirty Group is for DirtySprites.  Subclasses LayeredUpdates.
      pygame.sprite.LayeredDirty(*spites, **kwargs): return LayeredDirty
  
      This group requires pygame.sprite.DirtySprite or any sprite that
      has the following attributes:
          image, rect, dirty, visible, blendmode (see doc of DirtySprite).
      It uses the dirty flag technique and is therefore faster than the
      pygame.sprite.RenderUpdates if you have many static sprites.  It
      also switches automatically between dirty rect update and full
      screen drawing, so you do no have to worry what would be faster.
      Same as for the pygame.sprite.Group.
      You can specify some additional attributes through kwargs:
          _use_update: True/False   default is False
          _default_layer: default layer where sprites without a layer are added.
          _time_threshold: treshold time for switching between dirty rect mode
              and fullscreen mode, defaults to 1000./80  == 1000./fps
      New in pygame 1.8.0
      """
  
      def __init__(self, *sprites, **kwargs):
          """Same as for the pygame.sprite.Group.
          pygame.sprite.LayeredDirty(*spites, **kwargs): return LayeredDirty
          You can specify some additional attributes through kwargs:
          _use_update: True/False   default is False
          _default_layer: the default layer where the sprites without a layer are
                          added.
          _time_threshold: treshold time for switching between dirty rect mode and
                          fullscreen mode, defaults to 1000./80  == 1000./fps
          """
          LayeredUpdates.__init__(self, *sprites, **kwargs)
          self._clip = None
  
          self._use_update = False
  
          self._time_threshold = 1000. / 80.  # 1000./ fps
  
          self._bgd = None
          for key, val in kwargs.items():
              if key in ['_use_update', '_time_threshold', '_default_layer']:
                  if hasattr(self, key):
                      setattr(self, key, val)
  
      def add_internal(self, sprite, layer=None):
          """Do not use this method directly. It is used by the group to add a
          sprite internally.
          """
          # check if all attributes needed are set
          if not hasattr(sprite, 'dirty'):
              raise AttributeError()
          if not hasattr(sprite, "visible"):
              raise AttributeError()
          if not hasattr(sprite, "blendmode"):
              raise AttributeError()
  
          if not isinstance(sprite, DirtySprite):
              raise TypeError()
  
          if sprite.dirty == 0:  # set it dirty if it is not
              sprite.dirty = 1
  
          LayeredUpdates.add_internal(self, sprite, layer)
  
      def draw(self, surface, bgd=None):
          """draw all sprites in the right order onto the passed surface.
          LayeredDirty.draw(surface, bgd=None): return Rect_list
          You can pass the background too. If a background is already set,
          then the bgd argument has no effect.
          """
          # speedups
          _orig_clip = surface.get_clip()
          _clip = self._clip
          if _clip is None:
              _clip = _orig_clip
  
          _surf = surface
          _sprites = self._spritelist
          _old_rect = self.spritedict
          _update = self.lostsprites
          _update_append = _update.append
          _ret = None
          _surf_blit = _surf.blit
          _rect = Rect
          if bgd is not None:
              self._bgd = bgd
          _bgd = self._bgd
  
          _surf.set_clip(_clip)
          # -------
          # 0. deside if normal render of flip
          start_time = get_ticks()
          if self._use_update:  # dirty rects mode
              # 1. find dirty area on screen and put the rects into _update
              # still not happy with that part
              for spr in _sprites:
                  if 0 < spr.dirty:
                      # chose the right rect
                      if spr.source_rect:
                          _union_rect = _rect(spr.rect.topleft, spr.source_rect.size)
                      else:
                          _union_rect = _rect(spr.rect)
  
                      _union_rect_collidelist = _union_rect.collidelist
                      _union_rect_union_ip = _union_rect.union_ip
                      i = _union_rect_collidelist(_update)
                      while -1 < i:
                          _union_rect_union_ip(_update[i])
                          del _update[i]
                          i = _union_rect_collidelist(_update)
                      _update_append(_union_rect.clip(_clip))
  
                      _union_rect = _rect(_old_rect[spr])
                      _union_rect_collidelist = _union_rect.collidelist
                      _union_rect_union_ip = _union_rect.union_ip
                      i = _union_rect_collidelist(_update)
                      while -1 < i:
                          _union_rect_union_ip(_update[i])
                          del _update[i]
                          i = _union_rect_collidelist(_update)
                      _update_append(_union_rect.clip(_clip))
              # can it be done better? because that is an O(n**2) algorithm in
              # worst case
  
              # clear using background
              if _bgd is not None:
                  for rec in _update:
                      _surf_blit(_bgd, rec, rec)
  
              # 2. draw
              for spr in _sprites:
                  if 1 > spr.dirty:
                      if spr._visible:
                          # sprite not dirty, blit only the intersecting part
                          _spr_rect = spr.rect
                          if spr.source_rect is not None:
                              _spr_rect = Rect(spr.rect.topleft, spr.source_rect.size)
                          _spr_rect_clip = _spr_rect.clip
                          for idx in _spr_rect.collidelistall(_update):
                              # clip
                              clip = _spr_rect_clip(_update[idx])
                              _surf_blit(spr.image, clip, \
                                         (clip[0] - _spr_rect[0], \
                                          clip[1] - _spr_rect[1], \
                                          clip[2], \
                                          clip[3]), spr.blendmode)
                  else:  # dirty sprite
                      if spr._visible:
                          _old_rect[spr] = _surf_blit(spr.image, spr.rect, \
                                                      spr.source_rect, spr.blendmode)
                      if spr.dirty == 1:
                          spr.dirty = 0
              _ret = list(_update)
          else:  # flip, full screen mode
              if _bgd is not None:
                  _surf_blit(_bgd, (0, 0))
              for spr in _sprites:
                  if spr._visible:
                      _old_rect[spr] = _surf_blit(spr.image, spr.rect, spr.source_rect, spr.blendmode)
              _ret = [_rect(_clip)]  # return only the part of the screen changed
  
          # timing for switching modes
          # how to find a good treshold? it depends on the hardware it runs on
          end_time = get_ticks()
          if end_time - start_time > self._time_threshold:
              self._use_update = False
          else:
              self._use_update = True
  
          ##        # debug
          ##        print "               check: using dirty rects:", self._use_update
  
          # emtpy dirty reas list
          _update[:] = []
  
          # -------
          # restore original clip
          _surf.set_clip(_orig_clip)
          return _ret
  
      def clear(self, surface, bgd):
          """used to set background
          Group.clear(surface, bgd): return None
          """
          self._bgd = bgd
  
      def repaint_rect(self, screen_rect):
          """repaints the given area
          LayeredDirty.repaint_rect(screen_rect): return None
          screen_rect is in screencoordinates.
          """
          self.lostsprites.append(screen_rect.clip(self._clip))
  
      def set_clip(self, screen_rect=None):
          """ clip the area where to draw. Just pass None (default) to reset the clip
          LayeredDirty.set_clip(screen_rect=None): return None
          """
          if screen_rect is None:
              self._clip = gsdl2.display.get_surface().get_rect()
          else:
              self._clip = screen_rect
          self._use_update = False
  
      def get_clip(self):
          """clip the area where to draw. Just pass None (default) to reset the clip
          LayeredDirty.get_clip(): return Rect
          """
          return self._clip
  
      def change_layer(self, sprite, new_layer):
          """changes the layer of the sprite
          change_layer(sprite, new_layer): return None
          sprite must have been added to the renderer. It is not checked.
          """
          LayeredUpdates.change_layer(self, sprite, new_layer)
          if sprite.dirty == 0:
              sprite.dirty = 1
  
      def set_timing_treshold(self, time_ms):
          """sets the treshold in milliseconds
          set_timing_treshold(time_ms): return None
          Default is 1000./80 where 80 is the fps I want to switch to full screen mode.
          """
          self._time_threshold = time_ms
  
  
  class GroupSingle(AbstractGroup):
      """A group container that holds a single most recent item.
         This class works just like a regular group, but it only
         keeps a single sprite in the group. Whatever sprite has
         been added to the group last, will be the only sprite in
         the group.
         You can access its one sprite as the .sprite attribute.
         Assigning to this attribute will properly remove the old
         sprite and then add the new one."""
  
      def __init__(self, sprite=None):
          AbstractGroup.__init__(self)
          self.__sprite = None
          if sprite is not None: self.add(sprite)
  
      def copy(self):
          return GroupSingle(self.__sprite)
  
      def sprites(self):
          if self.__sprite is not None:
              return [self.__sprite]
          else:
              return []
  
      def add_internal(self, sprite):
          if self.__sprite is not None:
              self.__sprite.remove_internal(self)
          self.__sprite = sprite
  
      def __nonzero__(self):
          return (self.__sprite is not None)
  
      def _get_sprite(self):
          return self.__sprite
  
      def _set_sprite(self, sprite):
          self.add_internal(sprite)
          sprite.add_internal(self)
          return sprite
  
      sprite = property(_get_sprite, _set_sprite, None,
                        "The sprite contained in this group")
  
      def remove_internal(self, sprite):
          if sprite is self.__sprite: self.__sprite = None
  
      def has_internal(self, sprite):
          return (self.__sprite is sprite)
  
      # Optimizations...
      def __contains__(self, sprite):
          return (self.__sprite is sprite)
  
  
  # some different collision detection functions that could be used.
  
  def collide_rect(left, right):
      """collision detection between two sprites, using rects.
      pygame.sprite.collide_rect(left, right): return bool
      Tests for collision between two sprites. Uses the
      pygame rect colliderect function to calculate the
      collision. Intended to be passed as a collided
      callback function to the *collide functions.
      Sprites must have a "rect" attributes.
      New in pygame 1.8.0
      """
      return left.rect.colliderect(right.rect)
  
  
  class collide_rect_ratio:
      """A callable class that checks for collisions between
      two sprites, using a scaled version of the sprites
      rects.
      Is created with a ratio, the instance is then intended
      to be passed as a collided callback function to the
      *collide functions.
      New in pygame 1.8.1
      """
  
      def __init__(self, ratio):
          """Creates a new collide_rect_ratio callable. ratio is
          expected to be a floating point value used to scale
          the underlying sprite rect before checking for
          collisions.
          """
  
          self.ratio = ratio
  
      def __call__(self, left, right):
          """pygame.sprite.collide_rect_ratio(ratio)(left, right): bool
          collision detection between two sprites, using scaled rects.
          Tests for collision between two sprites. Uses the
          pygame rect colliderect function to calculate the
          collision, after scaling the rects by the stored ratio.
          Sprites must have a "rect" attributes.
          """
  
          ratio = self.ratio
  
          leftrect = left.rect
          width = leftrect.width
          height = leftrect.height
          leftrect = leftrect.inflate(width * ratio - width, height * ratio - height)
  
          rightrect = right.rect
          width = rightrect.width
          height = rightrect.height
          rightrect = rightrect.inflate(width * ratio - width, height * ratio - height)
  
          return leftrect.colliderect(rightrect)
  
  
  def collide_circle(left, right):
      """collision detection between two sprites, using circles.
      pygame.sprite.collide_circle(left, right): return bool
      Tests for collision between two sprites, by testing to
      see if two circles centered on the sprites overlap. If
      the sprites have a "radius" attribute, that is used to
      create the circle, otherwise a circle is created that
      is big enough to completely enclose the sprites rect as
      given by the "rect" attribute. Intended to be passed as
      a collided callback function to the *collide functions.
      Sprites must have a "rect" and an optional "radius"
      attribute.
      New in pygame 1.8.0
      """
  
      xdistance = left.rect.centerx - right.rect.centerx
      ydistance = left.rect.centery - right.rect.centery
      distancesquared = xdistance ** 2 + ydistance ** 2
      try:
          leftradiussquared = left.radius ** 2
      except AttributeError:
          leftrect = left.rect
          leftradiussquared = (leftrect.width ** 2 + leftrect.height ** 2) / 4
      try:
          rightradiussquared = right.radius ** 2
      except AttributeError:
          rightrect = right.rect
          rightradiussquared = (rightrect.width ** 2 + rightrect.height ** 2) / 4
      return distancesquared < leftradiussquared + rightradiussquared
  
  
  class collide_circle_ratio(object):
      """A callable class that checks for collisions between
      two sprites, using a scaled version of the sprites radius.
      Is created with a ratio, the instance is then intended
      to be passed as a collided callback function to the
      *collide functions.
      New in pygame 1.8.1
      """
  
      def __init__(self, ratio):
          """Creates a new collide_circle_ratio callable. ratio is
          expected to be a floating point value used to scale
          the underlying sprite radius before checking for
          collisions.
          """
          self.ratio = ratio
          # Constant value that folds in division for diameter to radius,
          # when calculating from a rect.
          self.halfratio = ratio ** 2 / 4.0
  
      def __call__(self, left, right):
          """pygame.sprite.collide_circle_radio(ratio)(left, right): return bool
          collision detection between two sprites, using scaled circles.
          Tests for collision between two sprites, by testing to
          see if two circles centered on the sprites overlap, after
          scaling the circles radius by the stored ratio. If
          the sprites have a "radius" attribute, that is used to
          create the circle, otherwise a circle is created that
          is big enough to completely enclose the sprites rect as
          given by the "rect" attribute. Intended to be passed as
          a collided callback function to the *collide functions.
          Sprites must have a "rect" and an optional "radius"
          attribute.
          """
  
          ratio = self.ratio
          xdistance = left.rect.centerx - right.rect.centerx
          ydistance = left.rect.centery - right.rect.centery
          distancesquared = xdistance ** 2 + ydistance ** 2
          # Optimize for not containing radius attribute, as if radius was
          # set consistently, would probably be using collide_circle instead.
          if hasattr(left, "radius"):
              leftradiussquared = (left.radius * ratio) ** 2
  
              if hasattr(right, "radius"):
                  rightradiussquared = (right.radius * ratio) ** 2
              else:
                  halfratio = self.halfratio
                  rightrect = right.rect
                  rightradiussquared = (rightrect.width ** 2 + rightrect.height ** 2) * halfratio
          else:
              halfratio = self.halfratio
              leftrect = left.rect
              leftradiussquared = (leftrect.width ** 2 + leftrect.height ** 2) * halfratio
  
              if hasattr(right, "radius"):
                  rightradiussquared = (right.radius * ratio) ** 2
              else:
                  rightrect = right.rect
                  rightradiussquared = (rightrect.width ** 2 + rightrect.height ** 2) * halfratio
          return distancesquared < leftradiussquared + rightradiussquared
  
  
  def collide_mask(left, right):
      """collision detection between two sprites, using masks.
      pygame.sprite.collide_mask(SpriteLeft, SpriteRight): bool
      Tests for collision between two sprites, by testing if
      thier bitmasks overlap. If the sprites have a "mask"
      attribute, that is used as the mask, otherwise a mask is
      created from the sprite image. Intended to be passed as
      a collided callback function to the *collide functions.
      Sprites must have a "rect" and an optional "mask"
      attribute.
      New in pygame 1.8.0
      """
      xoffset = right.rect[0] - left.rect[0]
      yoffset = right.rect[1] - left.rect[1]
      try:
          leftmask = left.mask
      except AttributeError:
          leftmask = from_surface(left.image)
      try:
          rightmask = right.mask
      except AttributeError:
          rightmask = from_surface(right.image)
      return leftmask.overlap(rightmask, (xoffset, yoffset))
  
  
  def spritecollide(sprite, group, dokill, collided=None):
      """find Sprites in a Group that intersect another Sprite
      pygame.sprite.spritecollide(sprite, group, dokill, collided = None): return Sprite_list
      Return a list containing all Sprites in a Group that intersect with another
      Sprite. Intersection is determined by comparing the Sprite.rect attribute
      of each Sprite.
      The dokill argument is a bool. If set to True, all Sprites that collide
      will be removed from the Group.
      The collided argument is a callback function used to calculate if two sprites
      are colliding. it should take two sprites as values, and return a bool
      value indicating if they are colliding. If collided is not passed, all sprites
      must have a "rect" value, which is a rectangle of the sprite area, which will
      be used to calculate the collision.
      """
      crashed = []
      if collided is None:
          # Special case old behaviour for speed.
          spritecollide = sprite.rect.colliderect
          if dokill:
              for s in group.sprites():
                  if spritecollide(s.rect):
                      s.kill()
                      crashed.append(s)
          else:
              for s in group:
                  if spritecollide(s.rect):
                      crashed.append(s)
      else:
          if dokill:
              for s in group.sprites():
                  if collided(sprite, s):
                      s.kill()
                      crashed.append(s)
          else:
              for s in group:
                  if collided(sprite, s):
                      crashed.append(s)
      return crashed
  
  
  def groupcollide(groupa, groupb, dokilla, dokillb, collided=None):
      """pygame.sprite.groupcollide(groupa, groupb, dokilla, dokillb) -> dict
         collision detection between group and group
         given two groups, this will find the intersections
         between all sprites in each group. it returns a
         dictionary of all sprites in the first group that
         collide. the value for each item in the dictionary
         is a list of the sprites in the second group it
         collides with. the two dokill arguments control if
         the sprites from either group will be automatically
         removed from all groups.
         collided is a callback function used to calculate if
         two sprites are colliding. it should take two sprites
         as values, and return a bool value indicating if
         they are colliding. if collided is not passed, all
         sprites must have a "rect" value, which is a
         rectangle of the sprite area, which will be used
         to calculate the collision."""
      crashed = {}
      SC = spritecollide
      if dokilla:
          for s in groupa.sprites():
              c = SC(s, groupb, dokillb, collided)
              if c:
                  crashed[s] = c
                  s.kill()
      else:
          for s in groupa:
              c = SC(s, groupb, dokillb, collided)
              if c:
                  crashed[s] = c
      return crashed
  
  
  def spritecollideany(sprite, group, collided=None):
      """pygame.sprite.spritecollideany(sprite, group) -> sprite
         finds any sprites that collide
         given a sprite and a group of sprites, this will
         return return any single sprite that collides with
         with the given sprite. If there are no collisions
         this returns None.
         if you don't need all the features of the
         spritecollide function, this function will be a
         bit quicker.
         collided is a callback function used to calculate if
         two sprites are colliding. it should take two sprites
         as values, and return a bool value indicating if
         they are colliding. if collided is not passed, all
         sprites must have a "rect" value, which is a
         rectangle of the sprite area, which will be used
         to calculate the collision."""
      if collided is None:
          # Special case old behaviour for speed.
          spritecollide = sprite.rect.colliderect
          for s in group:
              if spritecollide(s.rect):
                  return s
      else:
          for s in group:
              if collided(sprite, s):
                  return s
      return None
  