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

210 Chapter 9

At u, we handle the pygame.QUIT event by setting our loop vari-

able keep_going to False.

The second if statement, at v, handles a new event type: the

pygame.MOUSEBUTTONDOWN event that tells us that the user has pressed

one of the mouse buttons. Whenever the user presses a mouse but-

ton, this event will appear in the list of events that our program

gets from pygame.event.get(), and we can use an if statement both

to check for the event and to tell the program what to do when the

event occurs. At w, we create a variable called spot to hold the x-

and y-coordinates of the mouse’s position. We can get the location

of the mouse-click event with event.pos; event is the current event in

our for loop. Our if statement has just verified that this particular

event is of type pygame.MOUSEBUTTONDOWN, and mouse events have a pos

attribute (in this case, event.pos) that stores the (x, y) coordinate

pair telling us where the mouse event occurred.

Once we know the location

on the screen where the user clicked

the mouse button, at x we tell the

program to draw a filled circle on

the screen surface, in the RED color

from our setup, at the location spot,

with the radius of 15 we specified in

our setup.

Putting It all together

The only thing left to do is update the display and tell our pro-

gram what to do when it’s time to exit. Here’s the full program for

ClickDots.py.

ClickDots.py

import pygame # Setup

pygame.init()

screen = pygame.display.set_mode([800,600])

pygame.display.set_caption("Click to draw")

keep_going = True

RED = (255,0,0) # RGB color triplet for RED

radius = 15

while keep_going: # Game loop

for event in pygame.event.get(): # Handling events

if event.type == pygame.QUIT:

keep_going = False