Harness for pysdl2
These are a set of classes to make easier to use pysdl2.
This is a work in progress so use it at your own risk!
- Python 3 (Python 2.7.x may work, but is not a priority!)
- SDL2 and SDL2_Mixer installed in your system
- Optionally SDL2_Image (otherwise only uncompressed BMP images are supported)
The easiest way to install Harness is using pip:
$ pip install pysdl2-harness
How does it looks like?
It is inspired by pyglet and specially focused on 2D games.
#!/usr/bin/env python from harness import Harness game = Harness(width=320, height=240, zoom=3) title = game.load_resource("title.bmp") @game.draw def draw(renderer): renderer.draw(title, 10, 10) @game.update def update(dt): if game.keys[game.KEY_ESCAPE]: game.quit() game.loop()
See harness module docstrings for a complete list of classes and methods.
There's an example game in
example.py and remember that you can still use
pysdl2 directly if you need to!
Harness tries to provide a clean and simple interface to the following components:
- The game loop
- Resource management
1. The game loop
Harness implements a game loop with a fixed frame rate determined by the vsync of the screen (usually 60 FPS), with support for fixed updates for the game logic (by default at 80 times per second).
The usual workflow is:
- Create a Harness object (we'll call it game in the examples).
- Load resources.
- Declare the draw and update functions.
- Run the
loop()method in your Harness instance.
The game loop should be called once and it will run until the game is quitted
Draw functions can be defined with the
draw decorator, and update
functions with the
The draw functions should expect a "renderer" parameter that allows to draw textures, bitmap fonts, etc.
game = Harness() tex = game.load_resource("bitmap.bmp") @game.draw def draw(renderer): renderer.draw(tex) game.loop()
The update function should expect a "dt" parameter that provides the delta
time (time elapsed between updates); in this case fixed at
(1 / UFPS).
game = Harness() @game.update def update(dt): print("%s elapsed since last update" % dt) game.loop()
Several draw and update functions can be defined and they will be run in the same order they were defined.
The game instance can be accessed from the update function to test for key states, quit the game, etc.
quit() can be used to exit the game loop.
game = Harness() @game.update def update(dt): if game.keys[game.KEY_ESCAPE]: game.quit() # in case we don't want to complete the update return game.loop()
A draw or update function can be removed from the game loop with
method, passing the function to be removed as parameter.
game = Harness() debug = False def update_debug(dt): print(dt) @game.update def update(dt): global debug if game.keys[game.KEY_D]: print("D was pressed!") if debug: # remove the update_debug update function game.remove_handler(update_debug) else: # add a new update function game.update(update_debug) debug = not debug # remove the key press once processed game.keys[game.KEY_D] = False if game.keys[game.KEY_ESCAPE]: game.quit() game.loop()
2. Loading resources
Resources can loaded with
load_resource() method. This method allows loading
resources searching for them in the paths specified in the
By default the files will be searched for in the "data" subdirectory at the same level as the script running the game.
Depending on the resource some extra libraries may be required in the system (eg, SDL_Image).
Resources not in use can be freed using
free_resources() method, but
be careful to not use any reference to the resource once it has been released.
Harness will free all resources after exiting the game loop.
2.1 Bitmap fonts
load_bitmap_font() can be used to load a image that will be used to draw
renderer.draw_text(). Harness will map a text string into a fixed
width and height part of the font image.
game = Harness() font = game.load_bitmap_font("font.png", width=6, height=10) @game.draw def draw(renderer): renderer.draw_text(font, 10, 10, "This is a text!") game.loop()
Fonts can be freed with
The state of the keys is exposed in
keys dictionary and it
gets updated in each game loop iteration.
Harness.KEY_* there are constants to test in the
keys dictionary. If a key
is being pressed, the value in the dictionary will be
game = Harness() @game.update def update(dt): if game.keys[game.KEY_ESCAPE]: game.quit() game.loop()
3.1 Game controllers
Game controllers can be mapped into key states so the game can access to the controller like the player was using the keyboard.
The default mapping is:
- DPad up: up arrow key
- DPad down: down arrow key
- DPad left: left arrow key
- DPad right: right arrow key
- Button A: key c
- Button B: key v
- Start button: key s
- Back button: escape key
Harness will manage the controller automatically in the game loop updating the
keys dictionary as needed.
has_controllers property can be checked to see if any game controller was
detected. Harness includes a game controller database with definitions for most
common devices, and SDL2 functions can be used to add more. If there's no information
about a given controller, it will be silently ignored.
In order to use a controller, the
controllers property can be accessed to
activate any detected controller.
game = Harness() # enumerate all detected controllers for controller in game.controllers: print(controller.name)
Once the controller has been activated, it can be deactivated using
The key mapping can be changed using the
set_mapping() method on the controller.
game = Harness() if game.has_controllers: # first controller controller = game.controllers # remap button a to key a controller.set_mapping(a="KEY_A")
The valid parameters are: up, down, left, right, a, b, start and back. Use a
string defining the key (see
The use of a controller won't disable the keyboard. If that is required, the game controllers can be accessed using SDL2 functions directly.
play() can be used to play a sample loaded with
loops parameter can be provided stating how many times the sample
will be repeated (use -1 for an infinite loop).
By default .ogg and .wav files are supported (in theory it could load any format supported by SDL_Mixer but Harness will only identify files with the aforementioned extensions).
play() returns the channel number used to play the sample and that
number can be used to muted the channel with
stop_playback() (if a channel
number s not provided, it will stop all channels).
Harness.AUDIO_CHANNELS channels are allocated (6 channels).
Harness can be used in a class to take advantage of object oriented programming
and avoid the use of global variables. Just use composition and register the
update and draw methods with
draw() instead of using the
from harness import Harness class MyGame(object): def __init__(self): self.harness = Harness() # register update and draw methods self.harness.update(self.update) self.harness.draw(self.draw) # load some resources self.image = self.harness.load_resource("image.png") def run(self): self.harness.loop() def update(self, dt): if self.harness.keys[self.harness.KEY_ESCAPE]: self.harness.quit() def draw(self, renderer): renderer.draw(self.image) if __name__ == "__main__": game = MyGame() game.run()
Author and Contributors
Juan J. Martinez <firstname.lastname@example.org>
This is free software under MIT license terms.
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