Code Robotron: 2084’s twin-stick action | Wireframe #38
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.
The new 116-page issue will be packed with more in-depth features, more previews and reviews, and more of the guides to game development that make the magazine what it is. The change means we’ll be able to bring you new subscription offers, and generally make the magazine more sustainable in a challenging global climate.
As for existing subscribers, we’ll be emailing you all to let you know how your subscription is changing, and we’ll have some special free issues on offer as a thank you for your support.
The first monthly issue will be out on 4 June, and subsequent editions will be published on the first Thursday of every month after that. You’ll be able to order a copy online, or you’ll find it in selected supermarkets and newsagents if you’re out shopping for essentials.
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.
Robotron: 2084
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 and on_key_up. The 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 on_key_up function.
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.
Here’s Mac’s code snippet, which creates a simple twin-stick shooting mechanic in Python. To get it working on your system, you’ll need to install Pygame Zero. And to download the full code and assets, go here.
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.
Get your copy of Wireframe issue 38
You can read more features like this one in Wireframe issue 38, available directly from Raspberry Pi Press — we deliver worldwide.
And if you’d like a handy digital version of the magazine, you can also download issue 38 for free in PDF format.
Make sure to follow Wireframe on Twitter and Facebook for updates and exclusive offers and giveaways. Subscribe on the Wireframe website to save up to 49% compared to newsstand pricing!
The post Code Robotron: 2084’s twin-stick action | Wireframe #38 appeared first on Raspberry Pi.
Comments
Post a Comment