Pygame

• We'll start by adding our variables.
• Add these lines of code directly below the gameState="running" line.

player1XPos = 100
player1YPos = 100

• The code will look like this:

• We then create Event Listeners in the game loop.
• To do this, change the lines that say print("left") and print("right") to say:

if event.type == pygame.KEYDOWN:
    if event.key == pygame.K_LEFT:
        player1XPos -= 5
    elif event.key == pygame.K_RIGHT:
        player1XPos += 5

• Your code should look like this:

• Run the program. You will find the player moves each time the key is pressed.
• This is good for some games but other times it is desirable to keep the player moving until another key is pressed (like in snake-type games). Currently the Event Listener and the Event Handler are in the same block of code.
• We will separate the two out for continous movement.
• We will need two new variables outside of the game loop to hold the player's speed and direction.
• The pseudocode for our new movement program is:

Set up variables:
   player1Direction = "nothing"
   player1Speed = 5
   player1XPos = 100
   player1YPos = 100

BEGIN LOOP
    Has the player used the mouse or keyboard?
       YES: Has the player pushed the left arrow?
	       YES: player1Direction is left
	    Has the player pushed the right arrow?
	       YES: player1Direction is right

    Is the player1Direction left?
	YES: Decrease the player1XPos variable by 5.
    Is the player1Direction right?
	YES: Increase the player1XPos variable by 5.

    Clear the screen, and draw the player1 shape at player1XPos, player1YPos. 
END LOOP

• Let's implement this in code.
• Add these variables underneath the player1YPos = 100 line:

player1Direction = ""
player1Speed = 5

• This should look like this:

• Next, we'll change the game loop to modify the event listener and all and event handler.
• Replace your game loop code with this code. Ensure you keep all the indents where they should be. You may find you need to tweak the indents with the tab key once you've pasted the code.

while gameState != "exit":  # game loop - note: everything in the mainloop is indented one tab
    for event in pygame.event.get():  # get user interaction events
        if event.type == pygame.QUIT:  # tests if window's X (close) has been clicked
            gameState = "exit"  # causes exit of game loop
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                # player1XPos -= 5
                player1Direction = "left"
            elif event.key == pygame.K_RIGHT:
                # player1XPos += 5
                player1Direction = "right"

    # Player 1 Event handler code now...
    if player1Direction == "left":
        player1XPos -= player1Speed
    elif player1Direction == "right":
        player1XPos += player1Speed

    screen.fill(black)
    player1 = pygame.draw.rect(screen, green, (player1XPos, player1YPos, 20, 20))

• This will look like this:

• Run the program with Shift-F10, and steer the square with the left/right cursor keys.
• What's different between this code and the previous version?
• Comment the lines of code to explain what they do.