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

224 Chapter 9

in every direction. In the final upgrade to this app, we’ll see an

even more impressive and powerful feature of sprite graphics that

handles detecting collisions.

SmileyPop, Version 1 .0

For our closing example, we’ll add one crucial bit of fun to the

SmileyExplosion.py program: the ability to “pop” the smiley

balloons/bubbles by clicking the right mouse button (or by pressing

the control key and clicking on a Mac). The effect is like a balloon-

popping game or Ant Smasher, Whack-a-Mole, and so on. We’ll be

able to create smiley balloons by dragging the left mouse button,

and we’ll pop them (that is, remove them from the screen) by click-

ing the right mouse button over one or more of the smiley sprites.

Detecting collisions and

removing sprites

The great news is that the Sprite class in Pygame comes with

collision detection built in. We can use the function pygame.sprite

.collide_rect() to check whether the rectangles holding two sprites

have collided; we can use the collide_circle() function to check

whether two round sprites are touching; and if we’re just check-

ing to see whether a sprite has collided with a single point (like

the pixel where the user just clicked the mouse), we can use a

sprite’s rect.collidepoint() function to check whether a sprite

overlaps, or collides with, that point on the screen.

If we’ve determined that the user clicked a point that touches

one or more sprites, we can remove each of those sprites from our

sprite_list group by calling the remove() function. We can handle

all the logic for popping smiley balloons in our MOUSEBUTTONDOWN event

handler code. To turn SmileyExplosion.py into SmileyPop.py, we’ll

just replace these two lines:

if event.type == pygame.MOUSEBUTTONDOWN:

mousedown = True

with the following seven lines of code:

if event.type == pygame.MOUSEBUTTONDOWN:
u if pygame.mouse.get_pressed()[0]: # Regular left mouse button, draw
mousedown = True