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File docs/reST/index.rst

   This was inspired by the annoying flash banner of the early 2000's.
   This tutorial examines every line of coded used in the example.
-`Sprite Module Introduction`_
+:doc:`Sprite Module Introduction <tut/SpriteIntro>`
   Pygame includes a higher level sprite module to help organize games.
   The sprite module includes several classes that help manage details found in almost all games types.
   The Sprite classes are a bit more advanced than the regular Pygame modules,

File docs/reST/tut/SpriteIntro.rst

+.. TUTORIAL:Sprite Module Introduction
+Pygame Tutorials - Sprite Module Introduction
+by Pete Shinners <>
+Revision 1.1, April 12th, 2002
+Pygame version 1.3 comes with a new module, ``pygame.sprite``. This module is
+written in python and includes some higher level classes to manage your game
+objects. By using this module to its full potential, you can easily manage and
+draw your game objects. The sprite classes are very optimized, so it's likely
+your game will run faster with the sprite module than without.
+The sprite module is also meant to be very generic. It turns out you can use it
+with nearly any type of gameplay. All this flexibility comes with a slight
+penalty, it needs a little understanding to properly use it. The
+:mod:`reference documentation <pygame.sprite>` for the sprite module can keep
+you running, but you'll probably need a bit more explanation of how to use
+:mod:pygame.sprite in your own game.
+Several of the pygame examples (like "chimp" and "aliens") have been updated to
+use the sprite module. You may want to look into those first to see what this
+sprite module is all about. The chimp module even has it's own line-by-line
+tutorial, which may help get more an understanding of programming with python
+and pygame.
+Note that this introduction will assume you have a bit of experience
+programming with python, and are somewhat framiliar with the different parts of
+creating a simple game.  In this tutorial the word "reference" is occasionally
+used.  This represents a python variable. Variables in python are references,
+so you can have several variables all pointing to the same object.
+History Lesson
+The term "sprite" is a holdover from older computer and game machines.  These
+older boxes were unable to draw and erase normal graphics fast enough for them
+to work as games. These machines had special hardware to handle game like
+objects that needed to animate very quickly. These objects were called
+"sprites" and had special limitations, but could be drawn and updated very
+fast. They usually existed in special overlay buffers in the video.  These days
+computers have become generally fast enough to handle sprite like objects
+without dedicated hardware. The term sprite is still used to represent just
+about anything in a 2D game that is animated.
+The Classes
+The sprite module comes with two main classes. The first is :class:`Sprite
+<pygame.sprite.Sprite>`, which should be used as a base class for all your game
+objects. This class doesn't really do anything on its own, it just includes
+several functions to help manage the game object. The other type of class is
+:class:`Group <pygame.sprite.Group>`. The ``Group`` class is a container for
+different ``Sprite`` objects. There are actually several different types of
+group classes. Some of the ``Groups`` can draw all the elements they contain,
+for example.
+This is all there really is to it. We'll start with a description of what each
+type of class does, and then discuss the proper ways to use these two classes.
+The Sprite Class
+As mentioned before, the Sprite class is designed to be a base class for all
+your game objects. You cannot really use it on its own, as it only has several
+methods to help it work with the different ``Group`` classes. The sprite keeps
+track of which groups it belongs to. The class constructor (:func:`__init__
+<pygame.sprite.Sprite.__init__>` method) takes an argument of a ``Group`` (or
+list of ``Groups``) the ``Sprite`` instance should belong to. You can also
+change the ``Group`` membership for the ``Sprite`` with the :func:`add()
+<pygame.sprite.Sprite.add>` and :func:`remove() <pygame.sprite.Sprite.remove>`
+methods.  There is also a :func:`groups() <pygame.sprite.Sprite.groups>`
+method, which returns a list of the current groups containing the sprite.
+When using the your Sprite classes it's best to think of them as "valid" or
+"alive" when they are belonging to one or more ``Groups``. When you remove the
+instance from all groups pygame will clean up the object. (Unless you have your
+own references to the instance somewhere else.) The :func:`kill()
+<pygame.sprite.Sprite.kill>` method removes the sprite from all groups it
+belongs to. This will cleanly delete the sprite object. If you've put some
+little games together, you'll know sometimes cleanly deleting a game object can
+be tricky. The sprite also comes with an :func:`alive()
+<pygame.sprite.Sprite.alive>` method, which returns true if it is still a
+member of any groups.
+The Group Class
+The ``Group`` class is just a simple container. Similar to the sprite, it has
+an :func:`add() <pygame.sprite.Group.add>` and :func:`remove()
+<pygame.sprite.Group.remove>` method which can change which sprites belong to
+the group. You also can pass a sprite or list of sprites to the constructor
+(:func:`__init__() <pygame.sprite.Group.__init__>` method) to create a ``Group``
+instance that contains some initial sprites.
+The ``Group`` has a few other methods like :func:`empty()
+<pygame.sprite.Group.empty>` to remove all sprites from the group and
+:func:`copy() <pygame.sprite.Group.copy>` which will return a copy of the group
+with all the same members. Also the :func:`has() <pygame.sprite.Group.has>`
+method will quickly check if the ``Group`` contains a sprite or list of
+The other function you will use frequently is the :func:`sprites()
+<pygame.sprite.Group.sprites>` method. This returns an object that can be
+looped on to access every sprite the group contains.  Currently this is just a
+list of the sprites, but in later version of python this will likely use
+iterators for better performance.
+As a shortcut, the ``Group`` also has an :func:`update()
+<pygame.sprite.Group.update>` method, which will call an ``update()`` method on
+every sprite in the group. Passing the same arguments to each one. Usually in a
+game you need some function that updates the state of a game object. It's very
+easy to call your own methods using the ``Group.sprites()`` method, but this is
+a shortcut that's used enough to be included. Also note that the base
+``Sprite`` class has a "dummy" ``update()`` method that takes any sort of
+arguments and does nothing.
+Lastly, the Group has a couple other methods that allow you to use it with 
+the builtin ``len()`` function, getting the number of sprites it contains, and 
+the "truth" operator, which allows you to do "if mygroup:" to check if the 
+group has any sprites.
+Mixing Them Together
+At this point the two classes seem pretty basic. Not doing a lot more than you
+can do with a simple list and your own class of game objects. But there are
+some big advantages to using the ``Sprite`` and ``Group`` together. A sprite
+can belong to as many groups as you want. Remember as soon as it belongs to no
+groups, it will usually be cleared up (unless you have other "non-group"
+references to that object).
+The first big thing is a fast simple way to categorize sprites. For example, 
+say we had a Pacman-like game. We could make separate groups for the different 
+types of objects in the game. Ghosts, Pac, and Pellets. When Pac eats a power 
+pellet, we can change the state for all ghost objects by effecting everything 
+in the Ghost group. This is quicker and simpler than looping through a list 
+of all the game objects and checking which ones are ghosts.
+Adding and removing groups and sprites from each other is a very fast
+operation, quicker than using lists to store everything. Therefore you can very
+efficiently change group memberships. Groups can be used to work like simple
+attributes for each game object. Instead of tracking some attribute like
+"close_to_player" for a bunch of enemy objects, you could add them to a
+separate group. Then when you need to access all the enemies that are near the
+player, you already have a list of them, instead of going through a list of all
+the enemies, checking for the "close_to_player" flag. Later on your game could
+add multiple players, and instead of adding more "close_to_player2",
+"close_to_player3" attributes, you can easily add them to different groups or
+each player.
+Another important benefit of using the ``Sprites`` and ``Groups``, the groups
+cleanly handle the deleting (or killing) of game objects. In a game where many
+objects are referencing other objects, sometimes deleting an object can be the
+hardest part, since it can't go away until it is not referenced by anyone. Say
+we have an object that is "chasing" another object. The chaser can keep a
+simple Group that references the object (or objects) it is chasing. If the
+object being chased happens to be destroyed, we don't need to worry about
+notifying the chaser to stop chasing. The chaser can see for itself that its
+group is now empty, and perhaps find a new target.
+Again, the thing to remember is that adding and removing sprites from groups is
+a very cheap/fast operation. You may be best off by adding many groups to
+contain and organize your game objects. Some could even be empty for large
+portions of the game, there isn't any penalties for managing your game like
+The Many Group Types
+The above examples and reasons to use ``Sprites`` and ``Groups`` are only a tip
+of the iceberg. Another advantage is that the sprite module comes with several
+different types of ``Groups``. These groups all work just like a regular old
+``Group``, but they also have added functionality (or slightly different
+functionality).  Here's a list of the ``Group`` classes included with the
+sprite module.
+This is the standard "no frills" group mainly explained above. Most of the 
+other ``Groups`` are derived from this one, but not all.
+This works exactly like the regular ``Group`` class, but it only contains 
+the most recently added sprite. Therefore when you add a sprite to this group, 
+it "forgets" about any previous sprites it had. Therefore it always contains 
+only one or zero sprites.
+This is a standard group derived from ``Group``. It has a draw() method 
+that draws all the sprites it contains to the screen (or any ``Surface``). For 
+this to work, it requires all sprites it contains to have a "image" and "rect" 
+attributes. It uses these to know what to blit, and where to blit it.
+This is derived from the ``RenderPlain`` group, and adds a method named
+``clear()``. This will erase the previous position of all drawn sprites. It
+uses a background image to fill in the areas where the sprite were. It is smart
+enough to handle deleted sprites and properly clear them from the screen when
+the ``clear()`` method is called.
+This is the cadillac of rendering ``Groups``. It is inherited from
+``RenderClear``, but changes the ``draw()`` method to also return a list of
+pygame ``Rects``, which represent all the areas on screen that have been
+That is the list of different groups available We'll discuss more about these
+rendering groups in the next section. There's nothing stopping you from
+creating your own Group classes as well. They are just python code, so you can
+inherit from one of these and add/change whatever you want. In the future I
+hope we can add a couple more ``Groups`` to this list. A ``GroupMulti`` which
+is like the ``GroupSingle``, but can hold up to a given number of sprites (in
+some sort of circular buffer?). Also a super-render group that can clear the
+position of the old sprites without needing a background image to do it (by
+grabbing a copy of the screen before blitting). Who knows really, but in the
+future we can add more useful classes to this list.
+The Rendering Groups
+From above we can see there are three different rendering groups. We could 
+probably just get away with the ``RenderUpdates`` one, but it adds overhead not 
+really needed for something like a scrolling game. So we have a couple tools 
+here, pick the right one for the right job.
+For a scrolling type game, where the background completely changes every frame.
+We obviously don't need to worry about python's update rectangles in the call
+to ``display.update()``. You should definitely go with the ``RenderPlain``
+group here to manage your rendering.
+For games where the background is more stationary, you definitely don't want
+pygame updating the entire screen (since it doesn't need to). This type of game
+usually involves erasing the old position of each object, then drawing it in a
+new place for each frame. This way we are only changing what is necessary.
+Most of the time you will just want to use the ``RenderUpdates`` class here.
+Since you will also want to pass this list of changes to the
+``display.update()`` function.
+The ``RenderUpdates`` class also does a good job an minimizing overlapping
+areas in the list of updated rectangles. If the previous position and current
+position of an object overlap, it will merge them into a single rectangle.
+Combine this with the fact that is properly handles deleted objects and this is
+one powerful ``Group`` class. If you've written a game that manages the changed
+rectangles for the objects in a game, you know this the cause for a lot of
+messy code in your game. Especially once you start to throw in objects that can
+be deleted at anytime. All this work is reduced down to a ``clear()`` and
+``draw()`` method with this monster class. Plus with the overlap checking, it
+is likely faster than if you did it yourself.
+Also note that there's nothing stopping you from mixing and matching these
+render groups in your game. You should definitely use multiple rendering groups
+when you want to do layering with your sprites. Also if the screen is split
+into multiple sections, perhaps each section of the screen should use an
+appropriate render group?
+Collision Detection
+The sprite module also comes with two very generic collision detection
+functions.  For more complex games, these really won't work for you, but you
+can easily grab the source code for them, and modify them as needed.
+Here's a summary of what they are, and what they do.
+``spritecollide(sprite, group, dokill) -> list``
+This checks for collisions between a single sprite and the sprites in a group.
+It requires a "rect" attribute for all the sprites used. It returns a list of
+all the sprites that overlap with the first sprite. The "dokill" argument is a
+boolean argument. If it is true, the function will call the ``kill()`` method
+on all the sprites. This means the last reference to each sprite is probably in
+the returned list. Once the list goes away so do the sprites.  A quick example
+of using this in a loop::
+    >>> for bomb in sprite.spritecollide(player, bombs, 1):
+    ...
+    ...     Explosion(bomb, 0)
+This finds all the sprites in the "bomb" group that collide with the player.
+Because of the "dokill" argument it deletes all the crashed bombs. For each
+bomb that did collide, it plays a "boom" sound effect, and creates a new
+``Explosion`` where the bomb was. (Note, the ``Explosion`` class here knows to
+add each instance to the appropriate class, so we don't need to store it in a
+variable, that last line might feel a little "funny" to you python programmers.
+``groupcollide(group1, group2, dokill1, dokill2) -> dictionary``
+This is similar to the ``spritecollide`` function, but a little more complex.
+It checks for collisions for all the sprites in one group, to the sprites in
+another. There is a ``dokill`` argument for the sprites in each list. When
+``dokill1`` is true, the colliding sprites in ``group1`` will be ``kill()``ed.
+When ``dokill2`` is true, we get the same results for ``group2``. The
+dictionary it returns works like this; each key in the dictionary is a sprite
+from ``group1`` that had a collision.  The value for that key is a list of the
+sprites that it collided with. Perhaps another quick code sample explains it
+    >>> for alien in sprite.groupcollide(aliens, shots, 1, 1).keys()
+    ...
+    ...     Explosion(alien, 0)
+    ...     kills += 1
+This code checks for the collisions between player bullets and all the aliens
+they might intersect. In this case we only loop over the dictionary keys, but
+we could loop over the ``values()`` or ``items()`` if we wanted to do something
+to the specific shots that collided with aliens. If we did loop over the
+``values()`` we would be looping through lists that contain sprites. The same
+sprite may even appear more than once in these different loops, since the same
+"shot" could have collided against multiple "aliens".
+Those are the basic collision functions that come with pygame. It should be
+easy to roll your own that perhaps use something different than the "rect"
+attribute. Or maybe try to fine-tweak your code a little more by directly
+effecting the collision object, instead of building a list of the collision?
+The code in the sprite collision functions is very optimized, but you could
+speed it up slightly by taking out some functionality you don't need.
+Common Problems
+Currently there is one main problem that catches new users. When you derive
+your new sprite class with the Sprite base, you **must** call the
+``Sprite.__init__()`` method from your own class ``__init__()`` method.  If you
+forget to call the ``Sprite.__init__()`` method, you get a cryptic error, like
+    AttributeError: 'mysprite' instance has no attribute '_Sprite__g'.
+Extending Your Own Classes *(Advanced)*
+Because of speed concerns, the current ``Group`` classes try to only do exactly
+what they need, and not handle a lot of general situations. If you decide you
+need extra features, you may want to create your own ``Group`` class.
+The ``Sprite`` and ``Group`` classes were designed to be extended, so feel free
+to create your own ``Group`` classes to do specialized things. The best place
+to start is probably the actual python source code for the sprite module.
+Looking at the current ``Sprite`` groups should be enough example on how to
+create your own.
+For example, here is the source code for a rendering ``Group`` that calls a
+``render()`` method for each sprite, instead of just blitting an "image"
+variable from it.  Since we want it to also handle updated areas, we will start
+with a copy of the original ``RenderUpdates`` group, here is the code::
+    class RenderUpdatesDraw(RenderClear):
+        """call sprite.draw(screen) to render sprites"""
+        def draw(self, surface):
+            dirty = self.lostsprites
+            self.lostsprites = []
+            for s, r in self.spritedict.items():
+                newrect = s.draw(screen) #Here's the big change
+                if r is 0:
+                    dirty.append(newrect)
+                else:
+                    dirty.append(newrect.union(r))
+                self.spritedict[s] = newrect
+            return dirty
+Following is more information on how you could create your own ``Sprite`` and
+``Group`` objects from scratch.
+The ``Sprite`` objects only "require" two methods. "add_internal()" and
+"remove_internal()".  These are called by the ``Group`` classes when they are
+removing a sprite from themselves. The ``add_internal()`` and
+``remove_internal()`` have a single argument which is a group. Your ``Sprite``
+will need some way to also keep track of the ``Groups`` it belongs to. You will
+likely want to try to match the other methods and arguments to the real
+``Sprite`` class, but if you're not going to use those methods, you sure don't
+need them.
+It is almost the same requirements for creating your own ``Group``. In fact, if
+you look at the source you'll see the ``GroupSingle`` isn't derived from the
+``Group`` class, it just implements the same methods so you can't really tell
+the difference. Again you need an "add_internal()" and "remove_internal()"
+method that the sprites call when they want to belong or remove themselves from
+the group. The ``add_internal()`` and ``remove_internal()`` have a single
+argument which is a sprite. The only other requirement for the ``Group``
+classes is they have a dummy attribute named "_spritegroup". It doesn't matter
+what the value is, as long as the attribute is present. The Sprite classes can
+look for this attribute to determine the difference between a "group" and any
+ordinary python container. (This is important, because several sprite methods
+can take an argument of a single group, or a sequence of groups. Since they
+both look similar, this is the most flexible way to "see" the difference.)
+You should through the code for the sprite module. While the code is a bit
+"tuned", it's got enough comments to help you follow along.  There's even a
+todo section in the source if you feel like contributing.