pygame / doc / tutorial / helloworld.rst

Hello World

Ahhh, the great tradition of saying "Hello World" in a programming language. To whet your appetite, we will do the same with a most simple application, which will display the typical Pygame logo. It is not important to understand anything at once, which will be used by the example. Nearly all parts used now are explained in later chapters, so do not hesitate, if the one or other explanation is missing.

Importing

Pygame2 uses a strict seperation of modules to allow you to build and import only those parts needed for your specific needs. In contrast to Pygame, this forces you to write more import statements, but the benefit is that you can keep your dependencies small.

Let's start with importing some basic SDL modules, which are necessary to display a small nice window and to do some basic drawing within that window.

import sys
import pygame2
import pygame2.examples
try:
    import pygame2.sdl.constants as constants
    import pygame2.sdl.image as image
    import pygame2.sdl.event as event
    import pygame2.sdl.video as video
except ImportError:
    print ("No pygame2.sdl support")
    sys.exit ()

First of all, we import the :mod:`pygame2` core module, which allows us to use some basic things, such as :class:`pygame2.Color` and :class:`pygame2.Rect` objects. In nearly all graphics applications written with pygame2, you will need the core.

Afterwards, we import the shipped examples. This is mainly done to have the logo around, which resides within the :mod:`pygame2.examples` package. In your own applications, it is unlikely that you will ever need to import them.

Finally, we try to get the :mod:`pygame2.sdl` modules, which are necessary for displaying the window and image. As Pygame2 can be built without SDL support, we add a typical safety net to get out without too much noise, if SDL support is not given.

Window Creation and Image Loading

Any graphical application requires access to the screen, mostly in form of a window, which basically represents a portion of the screen, the application has access to and the application can manipulate. Mostly, that portion has a border and title bar around it, so the user can move it around on the screen and reorganize anything, so it fits his needs.

Once we have imported all necessary parts, let's create a window to have access to the screen, so we can display the logo and thus represent it to the user.

video.init ()

imgresource = pygame2.examples.RESOURCES.get ("logo.bmp")
surface = image.load_bmp (imgresource)

screen = video.set_mode (surface.width + 10, surface.height + 10)

screen.fill (pygame2.Color (255, 255, 255))
screen.blit (surface, (5, 5))
screen.flip ()

First, we initialize the :mod:`pygame2.sdl.video` internals, so we can have access to the screen and create windows on top of it. Afterwards, we get the logo from the :mod:`pygame2.examples` package and create a :class:`pygame2.sdl.video.Surface` from it, which can be easily shown later on and which allows us to determine the minimum window size we need to display it.

Once done with that, :meth:`pygame2.sdl.video.set_mode` will create the window for us. We make the window slightly larger than the image size to have some small border around the image.

If the window is first created, it will appear all black on the screen by default. We change that by filling the window (which is nothing else than a special :class:`pygame2.sdl.video.Surface`) with a white color now and afterwards copy (which is called blitting) our loaded image to the window. As you can see, we are using (5, 5) as second argument to :meth:`pygame2.sdl.video.Surface.blit`. This is the top-left (x, y) offset to start copying the image contents at.

Tip

Try to experiment with different values instead of (5, 5), for example (-10, 8) or (17, -12) to learn more about the blit offset and its behaviour.

Finally, we have to instruct the window to tell the operating system or window manager that it should update the area where the window is located using :meth:`pygame2.sdl.video.Surface.flip`. This will cause the image to be shown.

Making the Application responsive

We are nearly done by now. We have an image to display, we have a window, where the image should be displayed on, so we can execute the written code, not?

Well, yes, but the only thing that will happen is that we will notice a short flickering before the application exits. Maybe we can even see the window with the logo for a short moment, but that's not what we want, do we?

To keep the window on the screen and to make it responsive to user input, such as closing the window, react upon the mouse cursor or key presses, we have to add a so-called event loop. The event loop will deal with certain types of actions happening on the window or while the window is focused by the user and - as long as the event loop is running - will keep the window shown on the screen [1].

okay = True
while okay:
    for ev in event.get ():
        if ev.type == constants.QUIT:
            okay = False
        if ev.type == constants.KEYDOWN and ev.key == constants.K_ESCAPE:
            okay = False

video.quit ()

TBD

Footnotes

[1]shown is not entirely true, but let's go with that for now.
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