Teach Your Kids To Code: A Parent-friendly Guide to Python Programming

User Interaction: Get into the Game 213

Next, we’ll add event handlers to our game loop. These event

handlers will set mousedown to True if the user is holding down the

mouse and False if not.

Game Loop: handling mouse Presses and releases

Make your game loop look like this:

while keep_going: # Game loop
for event in pygame.event.get(): # Handling events
if event.type == pygame.QUIT:
keep_going = False
u if event.type == pygame.MOUSEBUTTONDOWN:
v mousedown = True
w if event.type == pygame.MOUSEBUTTONUP:
x mousedown = False
y if mousedown: # Draw/update graphics
z spot = pygame.mouse.get_pos()
{ pygame.draw.circle(screen, YELLOW, spot, radius)
| pygame.display.update() # Update display

The game loop starts just like our other Pygame apps, but

at u, when we check to see whether the user has pressed one of

the mouse buttons, instead of drawing immediately, we set our

mousedown variable to True v. This will be the signal our program

needs to begin drawing.

The next if statement at w checks whether the user has

released the mouse button. If so, the line at x changes mousedown

back to False. This will let our game loop know to stop drawing

whenever the mouse button is up.

At y, our for loop is over (as we can see by the indentation),

and our game loop continues by checking whether the mouse button

is currently pressed (that is, if mousedown is True). If the mouse button

is down, the mouse is currently being dragged, so we want to allow

the user to draw on the screen.

At z, we get the current location of the mouse directly, with

spot = pygame.mouse.get_pos(), rather than pulling the position of the

last click, because we want to draw wherever the user is dragging

the mouse, not just at the location where they first pressed the but-

ton. At {, we draw the current circle on the screen surface, in the

color specified by YELLOW, at the (x, y) location spot where the mouse

is currently being dragged, with the radius of 15 that we specified

in the setup section of our code. Finally, we finish the game loop

at | by updating the display window with pygame.display.update().