from Raspberry Pi Blog – Raspberry Pi
Author Ryan Lambie
News flash! Before we get into our Robotron: 2084 code, we have some important news to share about Wireframe: as of issue 39, the magazine will be going monthly.
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We now return you to our usual programming…
Move in one direction and fire in another with this Python and Pygame re-creation of an arcade classic. Raspberry Pi’s own Mac Bowley has the code.
Robotron: 2084 is often listed on ‘best game of all time’ lists, and has been remade and re-released for numerous systems over the years.
Released back in 1982, Robotron: 2084 popularised the concept of the twin-stick shooter. It gave players two joysticks which allowed them to move in one direction while also shooting at enemies in another. Here, I’ll show you how to recreate those controls using Python and Pygame. We don’t have access to any sticks, only a keyboard, so we’ll be using the arrow keys for movement and
WASD to control the direction of fire.
The movement controls use a
global variable, a few
if statements, and two built-in Pygame functions:
on_key_down function is called when a key on the keyboard is pressed, so when the player presses the right arrow key, for example, I set the x direction of the player to be a positive 1. Instead of setting the movement to 1, instead, I’ll add 1 to the direction. The
on_key_down function is called when a button’s released. A key being released means the player doesn’t want to travel in that direction anymore and so we should do the opposite of what we did earlier – we take away the 1 or -1 we applied in the
We repeat this process for each arrow key. Moving the player in the
update() function is the last part of my movement; I apply a move speed and then use a
playArea rect to clamp the player’s position.
The arena background and tank sprites were created in Piskel. Separate sprites for the tank allow the turret to rotate separately from the tracks.
Turn and fire
Now for the aiming and rotating. When my player aims, I want them to set the direction the bullets will fire, which functions like the movement. The difference this time is that when a player hits an aiming key, I set the direction directly rather than adjusting the values. If my player aims up, and then releases that key, the shooting will stop. Our next challenge is changing this direction into a rotation for the turret.
Actors in Pygame can be rotated in degrees, so I have to find a way of turning a pair of x and y directions into a rotation. To do this, I use the math module’s
atan2 function to find the arc tangent of two points. The function returns a result in radians, so it needs to be converted. (You’ll also notice I had to adjust mine by 90 degrees. If you want to avoid having to do this, create a sprite that faces right by default.)
To fire bullets, I’m using a flag called ‘shooting’ which, when set to
True, causes my turret to turn and fire. My bullets are dictionaries; I could have used a class, but the only thing I need to keep track of is an actor and the bullet’s direction.
You can look at the
update function and see how I’ve implemented a fire rate for the turret as well. You can edit the
update function to take a single parameter,
dt, which stores the time since the last frame. By adding these up, you can trigger a bullet at precise intervals and then reset the timer.
This code is just a start – you could add enemies and maybe other player weapons to make a complete shooting experience.
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