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

212 Chapter 9

and MOUSEBUTTONUP events; in other words, we want to separate

mouse button clicks into presses and releases so that we know

when the mouse is being dragged (with the button down) versus

just being moved with the button up.

One way to accomplish this is with another Boolean flag vari-

able. We can set a Boolean called mousedown to True whenever the

user presses the mouse button and to False whenever the user

releases the mouse button. In our game loop, if the mouse but-

ton is down (in other words, when mousedown is True), we can get

the mouse’s location and draw a circle on the screen. If the pro-

gram is fast enough, the drawing should be smooth like in a

paintbrush app.

s tupe

Make the setup section of your code look like this:

import pygame # Setup

pygame.init()

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

u pygame.display.set_caption("Click and drag to draw")

keep_going = True

v YELLOW = (255,255,0) # RGB color triplet for YELLOW

radius = 15

w mousedown = False

The setup portion of our app looks like ClickDots.py, except for

the different window caption u, the YELLOW color we’ll be drawing

with v, and the very last line w. The Boolean variable mousedown

will be our flag variable to signal to the program that the mouse

button is down, or pressed.