README.md

##Paddle Game

Let's create our first game - grab the starter file [paddle starter.py](paddle starter.py) and copy it into a new Python window. Run it to see what it does!

Pretty simple so far, but we'll make improvements and turn it into a game. First, let's read the code to see what it is doing.

There are two functions provided called doRectsOverlap and isPointInsideRect. These are going to be used to detect if two objects have collided in the game.

def doRectsOverlap(rect1, rect2):
  for a, b in [(rect1, rect2), (rect2, rect1)]:
      # Check if a's corners are inside b
      if ((isPointInsideRect(a.left, a.top, b)) or
          (isPointInsideRect(a.left, a.bottom, b)) or
          (isPointInsideRect(a.right, a.top, b)) or
          (isPointInsideRect(a.right, a.bottom, b))):
          return True
  
  return False

def isPointInsideRect(x, y, rect):
    if (x > rect.left) and (x < rect.right) and (y > rect.top) and (y < rect.bottom):
        return True
    else:
        return False

There is also a whole section of code that creates all the variables used by the game. If we want to create more variables or change their starter values, this would be the place.

#the game's variables
ball_x = 50
ball_y = 50
ball_radius = 10
ball_color = [222,50,50]
ball_speed = 5
    
paddle_x = 200
paddle_y = 400
paddle_width = 60
paddle_height = 20
paddle_color = [20,180,180]
paddle_speed = 20

Inside the game loop there are a few things worth pointing out. The first is that the event loop checks for if you have pressed the left or right key. If you did, it will change some game variables.

for event in pygame.event.get():
#check if you've exited the game
    if event.type == pygame.QUIT:
        running = False

    #check if you pressed a key
    if event.type == pygame.KEYDOWN:
        if event.key == pygame.K_LEFT:
            paddle_x = paddle_x - paddle_speed
        if event.key == pygame.K_RIGHT:
            paddle_x = paddle_x + paddle_speed

The other new piece of code is for detecting collisions between the paddle and ball. First it creates a rectangle (that isn't drawn on the screen) around the ball and paddle, then uses the doRectsOverlap function to find out if they are touching. If they are it will print "YES" to the shell window.

#create imaginary rectangles around ball and paddle
ball_rect = pygame.Rect(ball_x-ball_radius, ball_y-ball_radius, ball_radius*2,ball_radius*2) #circles are measured from the center, so have to subtract 1 radius from the x and y
paddle_rect = pygame.Rect(paddle_x, paddle_y, paddle_width, paddle_height)
#see if the rectangles overlap
if doRectsOverlap(ball_rect, paddle_rect):
    print "YES"

##Steps to turn it into a game (can be done in any order)

####Challenge 1: Make the ball move in both the x and y direction and bounce off the walls

Refer to your code for the Day 5 animation projects for how to do it.

####Challenge 2: Make the ball bounce up when it hits the paddle

####Challenge 3: Create a score that increases every time you hit the ball

Here is some example code. The first line creates a font (this only needs to be done once, so not in the game loop). Then it renders it on the screen and blits it (these should happen in the game loop).

myfont = pygame.font.SysFont("Arial", 15)
label = myfont.render("Some text!", 1, pygame.color.THECOLORS['red'])
screen.blit(label, (100, 100))

####Challenge 4: Make the paddle be controlled by the mouse

KEYDOWN isn't the only event supported by Pygame. The following code is an example of how to use the MOUSEMOTION event to move your paddle:

if event.type == pygame.MOUSEMOTION:
    coordinates = pygame.mouse.get_pos() #gives (x,y) coordinates
    paddle_x = coordinates[0] #sets the paddle_x variable to the first item in coordinates

Check out http://www.pygame.org/docs/ref/event.html for the complete list of Pygame events. Also see the Key documentation for the complete list of key codes.

####Challenge 5: Don't allow the paddle to go off the screen

How can you add an if so that you don't ever move your paddle off the screen? Or put another way, if you paddle is off the screen, how can you move it back onto the screen?

####Challenge 6: Add a speed boost

How can you increase your ball speed 10% every time you hit it?

####Challenge 7: What should happen when the ball hits the bottom of the screen?

##Pong

Pong is a 2 player paddle game where you try to hit the ball past the other player's paddle. Can you turn your game into a 2 player game? You get a point every time you hit it past the other paddle. It will probably work best if you put the paddles moving up and down on the left and right sides of the screen.

Do 'Save as' so that you can save your pong game as a different file than your first paddle game (otherwise it will write over it).

To allow for the holding down of keys, add the following line of code before your game loop:

pygame.key.set_repeat(20, 20)

This will make sure the pygame.KEYDOWN event keeps firing every 20 ms while you are holding the key.

See [pong finished.py](finished/pong finished.py) for a complete example.

##Bonus Graphics Programs

There are more ideas fun graphics programs that you can make. Go to https://github.com/CoderDojoSV/beginner-python/tree/master/Extras#more-graphics-programs-to-try and check them out!