Conditional Practice with Pong

It’s the simplest game ever made. One moving spot, two score digits, and two paddles. — Allan Alcorn Pong (named after its distinctive sound) simulates table tennis is generally considered the first popular computer game. It was created in 1971 by Samuel Dabney in a makeshift workshop in his daughter’s bedroom with Nolan Bushnell and helped launch the first video game company, Atari. The first Pong console was installed in Andy Capp’s Tavern in Sunnyvale, California. It went on to be an incredible hit in stores and on home televisions, marking the beginning of the "arcade revolution". Pong is now part of the permanent collection at the Smithsonian Institution and part of the Video Game Hall of Fame. It even inspired mechanical toys. It had only two instructions: deposit quarter and avoid missing the ball for high score.

Getting Started

• Download this zip file to your computer and move it to a folder on your computer where you want to keep your programs for this course
• Unzip/Unarchive the file if you need to by double-clicking on it (your computer may do this automatically when downloading)
• Open PyCharm, press the Open button (or select File → Open), navigate to where you saved the folder, and select it
• You will need to Trust the project before it can be opened

Play the Game

In the Project Explorer panel, click the arrow beside the lab_pong project to expand the folder and show the single Python file inside that represents Pong.

Right-click on the file PongGame.py in the Project Explorer and select Run PongGame to play the game (you are welcome to look at all of the code, hopefully most of it will make sense to you). When the game starts, all the elements will be setup correctly, but it will not be playable. The ball will move until it goes off the screen in the upper right corner. You can move the paddles (read the code to figure out which keys to use!). If you click the mouse in the game window, it will reset the ball back to the center.

It draws all the basic game pieces but, without meaningful interaction, it is not a game!

Here is a video going over the organization of the code

Examine the game_step() Function

The heart of any video game is the "game loop" because it manages the entire game logic from responding to input, to updating the state of the game items, to enforcing the game's rules, to checking if the game's goals are met, to potentially much more (such as accurate physics, AI, remote players' actions, etc.). It is called a loop because it is responsible for managing the game actions repeatedly until the user quits. Each frame, or step, is called on many times per second (typically between 60 up to 120 times), thus the statistic frames per second, or FPS. Game loops are typically managed by a separate Game Engine so new games can be written by focusing just on the new code specific its characters, rules, and goals without worrying about the all the different platforms technical details (there are many popular engines like Unity or Unreal (made in NC!)).

In this simple program, you will write this important step yourself in the game_step() function, which needs to solve the following problems:

• move the ball based on its velocity (dx and dy values)
  This part is already done for you
• check if the ball hits top or bottom sides and, if so, bounce it off the side so it stays moving in game window
  We are not worrying about "real" physics in this game, so we can create a reasonable approximation of a bounce off a horizontal surface by simply reversing the ball's dy velocity value
• check if the ball got past Player 1's paddle by hitting the right edge
  This represents a miss by Player 1 so Player 2 scores a point. The ball should also be reset back to the center of the game window
• check if the ball got past Player 2's paddle by hitting the left edge
  This represents a miss by Player 2 so Player 1 scores a point. The ball should also be reset back to the center of the game window
• check if the ball hits Player 1's paddle by determining if both their x and y coordinates are closer than half their combined width and height respectively
  As a reminder, turtle shapes are roughly 21x21 pixels in size (multiplied by the values given to the shapesize() function)
  We are not worrying about "real" physics in this game, so we can create a reasonable approximation of a bounce off a vertical surface by simply reversing the ball's dx velocity value
• check if the ball hits Player 2's paddle by determining if both their x and y coordinates are closer than half their combined width and height respectively
  As a reminder, turtle shapes are roughly 21x21 pixels in size (multiplied by the values given to the shapesize() function)
  We are not worrying about "real" physics in this game, so we can create a reasonable approximation of a bounce off a vertical surface by simply reversing the ball's dx velocity value

You can solve these problems in any order you want, but code them and test them one at a time to make sure you limit the number of issues you have to deal with at once. Note, you can set the ball's initial velocity (dx and dy values) to whatever values you want so it tests the problem you are trying to solve quickly.

Remember to think about how to solve each problem before coding it and then to experiment with your solution to make sure you are confident in your solution.

Add Randomness

After you have a working game, change the reset_ball() function to launch the ball in a random direction by replacing the simple values (2, 2) used with calls to Python's random module. Note, your solution should ensure the ball moves reasonably towards one side or the other by:

• not letting it have too steep an angle (i.e., go almost straight up and down)
• not letting it go too fast or slow (i.e., the game should be fun to play)
• letting it move towards either player (i.e., moving in any quadrant should be possible)

Extending the Game

Once you have the basic game features working, add more features to experiment and make your game more fun to play.

Feel free to be creative, but remember to keep your ideas at your skill level since there are still many things we have yet to learn, but here are some ideas to get you started:

• give the game a theme by adding more to the background, changing how the ball and paddles are drawn (the original game had a dashed line down the middle)
• keep the paddles on the screen at all times (i.e., do not allow it to move outside the screen's bounds)
• make the speed of the ball increase as the game proceeds (i.e., accelerate its velocity over time)
• make the ball bounce off the paddle differently depending on where it hits (i.e., closer to completely reversing the ball's velocity (both dx and dy values) as you get closer to the outer edges of the paddle)
• end the game if either player reaches a certain score (the original game declared a winner at 11 points, look at how this was done in the Aim It Game code)
• make an additional blocker on each player's side that causes the ball to change direction (randomly or by bouncing, could also subtract points)

Some ideas include Pong Soccer, Ping Pong, Pong on the iPhone using its notch or "dynamic island", the many new elements included in the Steam Project:Pong game, or your experience with other real-world games.

In the comment at the top of the Python file add:

• Your name
• How long you spent coding it
• How to play your game (so I know how to play the game and what you intended to do and what is not completely working)
• Discussion of the fixed values you choose to make your game fun to play: the size of the game objects, movement speeds, , and any random ranges