Monday, 1st February 2010
Creating a Pygame window
In this first tutorial, we'll cover the basics and write some boilerplate code for Pygame - code you will almost always write whenever you use Pygame. We will:
- Create a Pygame window
- Stop the window from immediately disappearing
- Close the window in response to a quit event
- Change the title and background colour of the window
The complete code for this tutorial is shown at the bottom of this page.
The Pygame window
Since we are going to use the Pygame module, the first thing we need to do is import it.
We can now create a Pygame window object (which I've called 'screen') using
pygame.display.set_mode(). This object requires two values that define the width and height of the window. Rather than use constants, we'll define two variables, width and height, which will make the program easier to change later on. Feel free to use any integers that suit you. In order to display the window, we use the
(width, height) = (300, 200) screen = pygame.display.set_mode((width, height)) pygame.display.flip()
If you now run this program, you’ll see a 300 x 200 pixel window appear and then promptly disappear. The problem is that once as the
flip() function has been called, the end of the code is reached, so the program ends. To keep the screen visible for as long as we want, we need to make sure the program doesn't end. We could do this by adding an infinite loop.
while True: pass
The problem with an infinite loop is that, by definition, it never ends. The program won't quit even if we want it to. If we try to close the window by clicking on the X, nothing happens. You have to use Ctrl + C in the command line to force the program to quit.
We want our window to persist until the user chooses to closes it. To acheive this, we monitor user inputs (known as 'events') using
pygame.event.get(). This function returns a list of events which we can loop through and check to see whether any have the type QUIT. If we find such an event, we exit our loop, which is best done by changing a boolean variable (which I've called 'running').
running = True while running: for event in pygame.event.get(): if event.type == pygame.QUIT: running = False
The window now persists whilst 'running' is equal to
True, which it will be until you close the window (by clicking the X). Note that if you use an IDE for Python programming, then it may interfere with Pygame. This isn’t normally a major problem but it can stop the Pygame window from closing properly. If so, adding
pygame.quit() should solve the problem.
Changing the window's properties
Now we have a usable window, we can change its properties. For example, we can change its title using the
We can change the background colour by filling the screen object. Colours are defined using a 3-tuple of integers from 0 to 255, for the red, green and blue values respectively. For example, white is (255,255,255). Changes need to be made before the
flip() function is called.
background_colour = (255,255,255) screen.fill(background_colour)
The complete program, after a bit of rearrangement, should now look like this:
import pygame background_colour = (255,255,255) (width, height) = (300, 200) screen = pygame.display.set_mode((width, height)) pygame.display.set_caption('Tutorial 1') screen.fill(background_colour) pygame.display.flip() running = True while running: for event in pygame.event.get(): if event.type == pygame.QUIT: running = False
Running the program should create a window that looks like this (on Windows XP):
It's not very exciting at the moment, but now we have a window that persists until we close it. In the next tutorial we'll draw some shapes in our window and start our simulation by creating a Particle object.