
Tutorial 3: Better Pong
***********************


Contents
^^^^^^^^

* Tutorial 3: Better Pong

  * Adding Scoring

    * Making Enter Restart the Game

    * Giving Points to the Players

    * Displaying the Scores

      * New Resources

      * Drawing the HUD

      * Displaying the HUD

    * Giving Victory

  * Adding Sounds

    * Getting the Sounds

    * Loading the Sounds

    * Playing the Sounds

  * Adding Joystick Support

    * Axis Movement

    * Trackball Movement

    * Applying the Joystick Controls

  * The Final Result

In the last tutorial, we made a simple Pong game that was kind of
boring.  We're going to make it better by adding scores, sounds, and
joystick support.


Adding Scoring
==============

Adding a score system will make our Pong game feel more like a game
and less like a toy.  Every time a player wins a round, they will get
one point.  When a player gets ten points, they will win the game, and
a new game can be started by pressing the Enter key.


Making Enter Restart the Game
-----------------------------

We are going to need a new global variable: "game_in_progress". This
variable will indicate whether or not a game is currently going and
will be used to determine whether to start a new game or pause when
the Enter key is pressed.  Set it to "True" by default.

To make pressing Enter start a new game, we will check
"game_in_progress".  If a game is in progress, we will pause the game,
as we had it do previously.  Otherwise, we will set "game_in_progress"
to "True" and restart the room.

If you look through the documentation for "sge.dsp.Room", you may
notice that no "restart" method exists. In fact, this is a design
choice; earlier versions of the SGE did have a method to restart
rooms, but it was removed because this feature is overly difficult to
maintain properly.  But how do we restart the room, then? Well, we
technically don't.  Instead, we create a new room which is exactly
like the one we wanted to restart, and immediately start it.  We will
put the creation of the room into a new function, "create_room()".
Our definition of "Game.event_key_press()" becomes:

   def event_key_press(self, key, char):
       global game_in_progress

       if key == 'f8':
           sge.gfx.Sprite.from_screenshot().save('screenshot.jpg')
       elif key == 'f11':
           self.fullscreen = not self.fullscreen
       elif key == 'escape':
           self.event_close()
       elif key in ('p', 'enter'):
           if game_in_progress:
               self.pause()
           else:
               game_in_progress = True
               create_room().start()

Now, we need to define "create_room()".  This is very simple; we just
copy and paste the code we used at the bottom to create the room into
it, but specify that "player" and "player2" are global. Our function
is as follows:

   def create_room():
       global player1
       global player2
       player1 = Player(1)
       player2 = Player(2)
       ball = Ball()
       return sge.dsp.Room([player1, player2, ball], background=background)

Of course, this makes the identical code at the bottom redundant, so
we will replace it with a call to "create_room()".


Giving Points to the Players
----------------------------

We now need to add score attributes to the "Player" objects.  We will
initialize the new attribute, "score", in "Player.event_create()" as
"0".

Now, in "Ball.event_step()", add lines to increase "player1.score" and
"player2.score" whenever the respective player wins a round.


Displaying the Scores
---------------------

The players have points, but can't see the score!  We need to add a
HUD (heads-up display) to show the score to the players.

There are a couple of ways we can do this.  Most obviously, we can use
"sge.dsp.Game.project_text()" or "sge.dsp.Room.project_text()".
However, there is a much better way: have a dynamically generated
sprite that represents the look of the HUD at any given time, and
displaying that sprite.


New Resources
~~~~~~~~~~~~~

We need to add a new global variable called "hud_sprite".  Assign a
new sprite to this variable with a "width" of "320", a "height" of
"120", an "origin_x" of "160", and an "origin_y" of "0".

To draw text, we need a font.  Create a new "sge.gfx.Font" object and
assign it to "hud_font".  For now, we will use a system font. I am
choosing ""Droid Sans Mono"", but you can choose whatever font you
prefer.  Pass your choice as the first argument to
"sge.gfx.Font.__init__()".  Set the "size" keyword argument to "48".

Note: We are using system fonts for simplicity, but it is generally
  a bad idea to rely on them.  There is no standard for what fonts are
  available on the system, and the set of fonts available on the
  system varies widely.  In real projects, it is better to distribute
  a font file with the game and use that.


Drawing the HUD
~~~~~~~~~~~~~~~

There are a few times we need to redraw the HUD: when the game starts,
when player 1 scores, and when player 2 scores.  Therefore, we will
put the redrawing code into a function, "refresh_hud()".  This
function needs to clear the HUD sprite, draw Player 1's score, and
then draw Player 2's score.

Another constant is needed: "TEXT_OFFSET", which we will define as
"16".

We clear the HUD sprite with "sge.gfx.Sprite.draw_clear()".

To draw the text, we use "sge.gfx.Sprite.draw_text()".  Both calls
have a few arguments in common: "font" is set to "hud_font", "y" is
set to "TEXT_OFFSET", "color" is set to white, and "valign" is set to
""top"".

The rest of the arguments are different between the two.  "text" is
set to the respective player's score, converted to a string.  "x" is
set to "hud_sprite.width / 2 - TEXT_OFFSET" for player 1's score, and
"hud_sprite.width / 2 + TEXT_OFFSET" for player 2's score.  "halign"
is set to ""right"" for player 1's score, and ""left"" for player 2's
score.

"refresh_hud()" ends up something like this:

   def refresh_hud():
       # This fixes the HUD sprite so that it displays the correct score.
       hud_sprite.draw_clear()
       x = hud_sprite.width / 2
       hud_sprite.draw_text(hud_font, str(player1.score), x - TEXT_OFFSET,
                            TEXT_OFFSET, color=sge.gfx.Color("white"),
                            halign="right", valign="top")
       hud_sprite.draw_text(hud_font, str(player2.score), x + TEXT_OFFSET,
                            TEXT_OFFSET, color=sge.gfx.Color("white"),
                            halign="left", valign="top")

Add calls to "refresh_hud()" in the three places where a
"Player.score" value changes, right after the change.  These places
are in "Player.event_create()" and "Ball.event_step()".

we have one more problem.  "refresh_hud()" requires "player1" and
"player2" to each have an attribute called "score", but the first time
it is called, one of the player objects has not had a chance to
initialize this attribute.  To work around this, add a class attribute
to "Player" called "score", and set it to "0". This will cause
"player1.score" and "player2.score" to be "0" in the event that the
respective object's "score" has not been initialized yet.


Displaying the HUD
~~~~~~~~~~~~~~~~~~

At this point, we have our HUD, but it isn't displayed.  We will fix
this simply by adding a step event to "Game" which projects the HUD
sprite onto the screen:

   def event_step(self, time_passed, delta_mult):
       self.project_sprite(hud_sprite, 0, self.width / 2, 0)

Unlike "sge.dsp.Room" projections, "sge.dsp.Game" projections are
relative to the screen.  Additionally, these projections are always on
top of everything else on the screen.  This is usually how we want a
HUD to be displayed, which is why we are using a "sge.dsp.Game"
projection instead of a "sge.dsp.Room" projection or "sge.dsp.Object"
object.

Note: You may notice that, when you pause the game, the HUD
  disappears. This is *not* a bug! This happens because the step event
  doesn't occur while the game is paused.  If you want the HUD to show
  up while the game is paused, project it in the paused step event,
  defined by "sge.dsp.Game.event_paused_step()", as well.


Giving Victory
--------------

At this point, we have scores, but no one ever officially wins.  We
need to end the game when someone gets 10 points.  We will go a little
further and replace the scores with text that says "WIN" and "LOSE"
for the winner and loser, respectively.

Define a new constant called "POINTS_TO_WIN" as "10".

In our case, the most convenient place to check for victory is within
"Ball.serve()".  Specifically, put the code that sets the speed of the
ball under a conditional that checks whether the "score" values of
both players are less than "POINTS_TO_WIN".  Add an "else" block below
that.  This is where a player has won the game.

Since the game is over, stop the movement of the ball by setting
"xvelocity" and "yvelocity" to "0".  We don't want any more scoring to
happen.

Now, draw the new text onto the HUD.  We do this using the same call
to "sge.gfx.Sprite.draw_text()" we used in "refresh_hud()", except
instead of drawing the scores converted to strings, we draw ""WIN"" or
""LOSE"" depending on whether or not the respective player's score is
greater than the other player's score.

Finally, set "game_in_progress" to "False".  Don't forget to declare
it with "global" first.

The new "Ball.serve()" looks something like this:

   def serve(self, direction=None):
       global game_in_progress

       if direction is None:
           direction = random.choice([-1, 1])

       self.x = self.xstart
       self.y = self.ystart

       if (player1.score < POINTS_TO_WIN and
               player2.score < POINTS_TO_WIN):
           # Next round
           self.xvelocity = BALL_START_SPEED * direction
           self.yvelocity = 0
       else:
           # Game Over!
           self.xvelocity = 0
           self.yvelocity = 0
           hud_sprite.draw_clear()
           x = hud_sprite.width / 2
           p1text = "WIN" if player1.score > player2.score else "LOSE"
           p2text = "WIN" if player2.score > player1.score else "LOSE"
           hud_sprite.draw_text(hud_font, p1text, x - TEXT_OFFSET,
                                TEXT_OFFSET, color=sge.gfx.Color("white"),
                                halign="right", valign="top")
           hud_sprite.draw_text(hud_font, p2text, x + TEXT_OFFSET,
                                TEXT_OFFSET, color=sge.gfx.Color("white"),
                                halign="left", valign="top")
           game_in_progress = False


Adding Sounds
=============

We have a complete Pong game now, but it's still a little quiet.
Let's make it more lively by adding some sounds.


Getting the Sounds
------------------

I would normally go to a database like OpenGameArt for sound effects,
but in this case, we are instead going to use a nice free/libre
program called Sfxr.  This program makes it easy to generate retro-
sounding sound effects, so it's perfect for Pong sounds.  Generate
three sounds: one for the ball bouncing off a paddle ("bounce.wav"),
one for the ball bouncing off a wall ("bounce_wall.wav"), and one for
the ball passing by a player ("score.wav").  Alternatively, you can
copy the sounds I generated from examples/data.  Create a folder in
your project directory with the name "data" and put your sounds in
this folder.

Note: Some file systems, like FAT32 and NTFS, are case-insensitive
  and will allow you to treat "bounce.wav" and "Bounce.wav" as if they
  are the same file name, but some, such as pretty much every Linux
  file system, are case-sensitive, meaning that "bounce.wav" and
  "Bounce.wav" are two completely different names; requesting one will
  never give you the other.  If you have a case-insensitive file
  system, be careful to not get the case wrong, or some people who
  play the game will face a crash that will be completely invisible to
  you!


Loading the Sounds
------------------

Sounds in the SGE are stored in "sge.snd.Sound" objects.  As the only
argument, indicate the full path to the file.  There are two ways to
indicate the path: using the current working directory as a base, and
using the directory of pong.py as a base.  Both of methods require the
"os" module, so be sure to add this to your list of imports.

The easiest way to get the path of the file is to use the current
working directory as a base, on the assumption that the current
working directory is also the directory that the "data" folder is
located in. This method is very simple; assuming we want the file
called "spam.wav", we would use this code:

   os.path.join("data", "spam.wav")

However, it is not always the case that the current working directory
is the appropriate location to search for the "data" folder.  It could
be that the current working directory is the user's home directory,
for instance.  To prevent the game from crashing in this case, define
a constant called "DATA", indicating the "data" directory relative to
the location of pong.py:

   DATA = os.path.join(os.path.dirname(__file__), "data")

"__file__" is a special variable indicating the full path to the
current file, i.e. pong.py in this case.  By getting the directory
name of the current file, we can be certain of where to look for the
"data" folder.  "DATA" now indicates the appropriate path to the
"data" folder, so from now on, if we want a file called "spam.wav"
located in this directory, we use this code:

   os.path.join(DATA, "spam.wav")

Assign the appropriate "sge.snd.Sound" objects to "bounce_sound",
"bounce_wall_sound", and "score_sound".


Playing the Sounds
------------------

Sounds are played with "sge.snd.Sound.play()".  Call this method in
the appropriate places: when a player scores, when the ball bounces
off an edge of the screen, and when the ball hits a paddle.  There are
five places in total.

With that, our Pong game now has sound effects.


Adding Joystick Support
=======================

Joystick support is a nice thing to have in a game, so we are going to
add it.  We are going to support analog sticks and trackballs.  Mouse
control would actually be even better, but this would put one of the
players at an unfair advantage.

First, we will add an attribute to "Player" indicating what joystick
to use, called "joystick".  Set it to "0" (which is the first
joystick) for player 1, and "1" (which is the second joystick) for
player 2.


Axis Movement
-------------

Adding movement based on a joystick axis is easy.  For this, we use
"sge.joystick.get_axis()" in the step event of "Player". Pass
"self.joystick" as the first argument, and "1" (which is the Y-axis)
as the second argument.  Assign it to a variable called "axis_motion".
Later, we will be modifying the code that sets "yvelocity" so that it
is chosen based on axis position, trackball movement, or key presses,
whichever one would cause it to move fastest.


Trackball Movement
------------------

Since trackball motion is relative, it is a little trickier.  We need
to store the amount of movement it makes each frame.  We will use an
attribute called "trackball_motion" for that; initialize it as "0" in
the create event.

We now need to define the trackball move event, which is defined by
"sge.dsp.Object.event_joystick_trackball_move()".  Within this event,
if the "joystick" argument is the same as "self.joystick", add "y" to
"self.trackball_motion".  We are adding to it, rather than replacing
it, because the trackball might move multiple times in the same frame.


Applying the Joystick Controls
------------------------------

Currently, we have this line:

   self.yvelocity = key_motion * PADDLE_SPEED

This line uses the state of the keys to determine how to move the
paddle.  We need to change this so that the joystick controls we
defined can be used as well.  It will be replaced with the following:

* If the absolute value of "axis_motion" is greater than the
  absolute value of both "key_motion" and "trackball_motion", set
  "yvelocity" to "axis_motion * PADDLE_SPEED".

* Otherwise, if "trackball_motion" is greater than "key_motion", set
  "yvelocity" to "self.trackball_motion * PADDLE_SPEED"

* Otherwise, use the line we have been using up until this point.

After this, we must set "trackball_motion" to "0".


The Final Result
================

Our final Pong game now has scores, sounds, and even joystick support:

   #!/usr/bin/env python3

   # Pong Example
   # Written in 2013-2015 by Julie Marchant <onpon4@riseup.net>
   #
   # To the extent possible under law, the author(s) have dedicated all
   # copyright and related and neighboring rights to this software to the
   # public domain worldwide. This software is distributed without any
   # warranty.
   #
   # You should have received a copy of the CC0 Public Domain Dedication
   # along with this software. If not, see
   # <http://creativecommons.org/publicdomain/zero/1.0/>.

   import random

   import sge

   DATA = os.path.join(os.path.dirname(__file__), "data")
   PADDLE_XOFFSET = 32
   PADDLE_SPEED = 4
   PADDLE_VERTICAL_FORCE = 1 / 12
   BALL_START_SPEED = 2
   BALL_ACCELERATION = 0.2
   BALL_MAX_SPEED = 15
   POINTS_TO_WIN = 10
   TEXT_OFFSET = 16

   game_in_progress = True


   class Game(sge.dsp.Game):

       def event_step(self, time_passed, delta_mult):
           self.project_sprite(hud_sprite, 0, self.width / 2, 0)

       def event_key_press(self, key, char):
           global game_in_progress

           if key == 'f8':
               sge.gfx.Sprite.from_screenshot().save('screenshot.jpg')
           elif key == 'f11':
               self.fullscreen = not self.fullscreen
           elif key == 'escape':
               self.event_close()
           elif key in ('p', 'enter'):
               if game_in_progress:
                   self.pause()
               else:
                   game_in_progress = True
                   self.current_room.start()

       def event_close(self):
           self.end()

       def event_paused_key_press(self, key, char):
           if key == 'escape':
               # This allows the player to still exit while the game is
               # paused, rather than having to unpause first.
               self.event_close()
           else:
               self.unpause()

       def event_paused_close(self):
           # This allows the player to still exit while the game is paused,
           # rather than having to unpause first.
           self.event_close()


   class Player(sge.dsp.Object):

       score = 0

       def __init__(self, player):
           if player == 1:
               self.joystick = 0
               self.up_key = "w"
               self.down_key = "s"
               x = PADDLE_XOFFSET
               self.hit_direction = 1
           else:
               self.joystick = 1
               self.up_key = "up"
               self.down_key = "down"
               x = sge.game.width - PADDLE_XOFFSET
               self.hit_direction = -1

           y = sge.game.height / 2
           super().__init__(x, y, sprite=paddle_sprite, checks_collisions=False)

       def event_create(self):
           self.score = 0
           refresh_hud()
           self.trackball_motion = 0

       def event_step(self, time_passed, delta_mult):
           # Movement
           key_motion = (sge.keyboard.get_pressed(self.down_key) -
                         sge.keyboard.get_pressed(self.up_key))
           axis_motion = sge.joystick.get_axis(self.joystick, 1)

           if (abs(axis_motion) > abs(key_motion) and
                   abs(axis_motion) > abs(self.trackball_motion)):
               self.yvelocity = axis_motion * PADDLE_SPEED
           elif abs(self.trackball_motion) > abs(key_motion):
               self.yvelocity = self.trackball_motion * PADDLE_SPEED
           else:
               self.yvelocity = key_motion * PADDLE_SPEED

           self.trackball_motion = 0

           # Keep the paddle inside the window
           if self.bbox_top < 0:
               self.bbox_top = 0
           elif self.bbox_bottom > sge.game.current_room.height:
               self.bbox_bottom = sge.game.current_room.height

       def event_joystick_trackball_move(self, joystick, ball, x, y):
           if joystick == self.joystick:
               self.trackball_motion += y


   class Ball(sge.dsp.Object):

       def __init__(self):
           x = sge.game.width / 2
           y = sge.game.height / 2
           super().__init__(x, y, sprite=ball_sprite)

       def event_create(self):
           self.serve()

       def event_step(self, time_passed, delta_mult):
           # Scoring
           if self.bbox_right < 0:
               player2.score += 1
               refresh_hud()
               score_sound.play()
               self.serve(-1)
           elif self.bbox_left > sge.game.current_room.width:
               player1.score += 1
               refresh_hud()
               score_sound.play()
               self.serve(1)

           # Bouncing off of the edges
           if self.bbox_bottom > sge.game.current_room.height:
               self.bbox_bottom = sge.game.current_room.height
               self.yvelocity = -abs(self.yvelocity)
               bounce_wall_sound.play()
           elif self.bbox_top < 0:
               self.bbox_top = 0
               self.yvelocity = abs(self.yvelocity)
               bounce_wall_sound.play()

       def event_collision(self, other, xdirection, ydirection):
           if isinstance(other, Player):
               if other.hit_direction == 1:
                   self.bbox_left = other.bbox_right + 1
               else:
                   self.bbox_right = other.bbox_left - 1

               self.xvelocity = min(abs(self.xvelocity) + BALL_ACCELERATION,
                                    BALL_MAX_SPEED) * other.hit_direction
               self.yvelocity += (self.y - other.y) * PADDLE_VERTICAL_FORCE
               bounce_sound.play()

       def serve(self, direction=None):
           global game_in_progress

           if direction is None:
               direction = random.choice([-1, 1])

           self.x = self.xstart
           self.y = self.ystart

           if (player1.score < POINTS_TO_WIN and
                   player2.score < POINTS_TO_WIN):
               # Next round
               self.xvelocity = BALL_START_SPEED * direction
               self.yvelocity = 0
           else:
               # Game Over!
               self.xvelocity = 0
               self.yvelocity = 0
               hud_sprite.draw_clear()
               x = hud_sprite.width / 2
               p1text = "WIN" if player1.score > player2.score else "LOSE"
               p2text = "WIN" if player2.score > player1.score else "LOSE"
               hud_sprite.draw_text(hud_font, p1text, x - TEXT_OFFSET,
                                    TEXT_OFFSET, color=sge.gfx.Color("white"),
                                    halign="right", valign="top")
               hud_sprite.draw_text(hud_font, p2text, x + TEXT_OFFSET,
                                    TEXT_OFFSET, color=sge.gfx.Color("white"),
                                    halign="left", valign="top")
               game_in_progress = False


   def create_room():
       global player1
       global player2
       player1 = Player(1)
       player2 = Player(2)
       ball = Ball()
       return sge.dsp.Room([player1, player2, ball], background=background)


   def refresh_hud():
       # This fixes the HUD sprite so that it displays the correct score.
       hud_sprite.draw_clear()
       x = hud_sprite.width / 2
       hud_sprite.draw_text(hud_font, str(player1.score), x - TEXT_OFFSET,
                            TEXT_OFFSET, color=sge.gfx.Color("white"),
                            halign="right", valign="top")
       hud_sprite.draw_text(hud_font, str(player2.score), x + TEXT_OFFSET,
                            TEXT_OFFSET, color=sge.gfx.Color("white"),
                            halign="left", valign="top")


   # Create Game object
   Game(width=640, height=480, fps=120, window_text="Pong")

   # Load sprites
   paddle_sprite = sge.gfx.Sprite(width=8, height=48, origin_x=4, origin_y=24)
   ball_sprite = sge.gfx.Sprite(width=8, height=8, origin_x=4, origin_y=4)
   paddle_sprite.draw_rectangle(0, 0, paddle_sprite.width, paddle_sprite.height,
                                fill=sge.gfx.Color("white"))
   ball_sprite.draw_rectangle(0, 0, ball_sprite.width, ball_sprite.height,
                              fill=sge.gfx.Color("white"))
   hud_sprite = sge.gfx.Sprite(width=320, height=120, origin_x=160, origin_y=0)

   # Load backgrounds
   layers = [sge.gfx.BackgroundLayer(paddle_sprite, sge.game.width / 2, 0, -10000,
                                     repeat_up=True, repeat_down=True)]
   background = sge.gfx.Background(layers, sge.gfx.Color("black"))

   # Load fonts
   hud_font = sge.gfx.Font("Droid Sans Mono", size=48)

   # Load sounds
   bounce_sound = sge.snd.Sound(os.path.join(DATA, 'bounce.wav'))
   bounce_wall_sound = sge.snd.Sound(os.path.join(DATA, 'bounce_wall.wav'))
   score_sound = sge.snd.Sound(os.path.join(DATA, 'score.wav'))

   # Create rooms
   sge.game.start_room = create_room()

   sge.game.mouse.visible = False


   if __name__ == '__main__':
       sge.game.start()
