7 Steps To Writing A Game Engine In Rust

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Writing a game engine is a daunting task that requires a deep understanding of computer science, software engineering, and game development. Rust, with its focus on safety, performance, and conciseness, is an excellent language for building a game engine. In this article, we will explore the 7 steps to writing a game engine in Rust, from setting up the project to implementing graphics and physics.

Step 1: Setting Up the Project

Before we dive into the code, we need to set up our project. We will use Cargo, Rust's package manager, to create a new project. Run the following command in your terminal:

cargo new game_engine

This will create a new directory called game_engine with a basic Cargo.toml file and a src directory. We will add our dependencies to the Cargo.toml file as we progress.

Choosing the Right Dependencies

For a game engine, we will need to handle graphics, input, and physics. We will use the following dependencies:

• winit for window management and input handling
• wgpu for graphics rendering
• nalgebra for linear algebra and vector calculations
• rapier for physics simulations

Add the following lines to your Cargo.toml file:

[dependencies]
winit = "0.27.3"
wgpu = "0.13.1"
nalgebra = "0.31.1"
rapier = "0.10.0"

Step 2: Building the Window and Input System

Our game engine will need a window to render graphics and handle user input. We will use winit to create a window and handle input events.

Create a new file called window.rs in the src directory and add the following code:

use winit::{
    event::{Event, VirtualKeyCode},
    event_loop::{ControlFlow, EventLoop},
    window::WindowBuilder,
};

pub struct Window {
    event_loop: EventLoop<()>,
    window: winit::window::Window,
}

impl Window {
    pub fn new() -> Self {
        let event_loop = EventLoop::new();
        let window = WindowBuilder::new()
           .with_title("Game Engine")
           .with_width(800)
           .with_height(600)
           .build(&event_loop)
           .unwrap();

        Window { event_loop, window }
    }

    pub fn run(&mut self) {
        self.event_loop.run(move |event, _, control_flow| {
            *control_flow = ControlFlow::Wait;

            match event {
                Event::WindowEvent { event,.. } => match event {
                    winit::event::WindowEvent::CloseRequested => *control_flow = ControlFlow::Exit,
                    winit::event::WindowEvent::KeyboardInput {
                        input:
                            winit::event::KeyboardInput {
                                virtual_keycode: Some(VirtualKeyCode::Escape),
                               ..
                            },
                       ..
                    } => *control_flow = ControlFlow::Exit,
                    _ => (),
                },
                _ => (),
            }
        });
    }
}

Step 3: Implementing Graphics Rendering

Our game engine will use wgpu to handle graphics rendering. We will create a new file called renderer.rs in the src directory and add the following code:

use wgpu::*;

pub struct Renderer {
    device: Device,
    queue: Queue,
    config: SurfaceConfiguration,
    surface: Surface,
}

impl Renderer {
    pub fn new(window: &Window) -> Self {
        let instance = Instance::new(Backends::all());
        let surface = unsafe { instance.create_surface(window) };
        let adapter = instance
           .request_adapter(&RequestAdapterOptions {
                power_preference: PowerPreference::default(),
                force_fallback_adapter: false,
                compatible_surface: Some(&surface),
            })
           .await
           .unwrap();

        let (device, queue) = adapter
           .request_device(
                &DeviceDescriptor {
                    label: None,
                    features: Features::empty(),
                    limits: Limits::downlevel_webgl2_defaults(),
                },
                None,
            )
           .await
           .unwrap();

        let config = SurfaceConfiguration {
            usage: TextureUsages::RENDER_ATTACHMENT,
            format: surface.get_supported_formats(&adapter)[0],
            width: window.window.inner_size().width,
            height: window.window.inner_size().height,
            present_mode: PresentMode::Fifo,
        };
        surface.configure(&device, &config);

        Renderer {
            device,
            queue,
            config,
            surface,
        }
    }

    pub fn render(&mut self) {
        let frame = self.surface.get_current_texture().unwrap();
        let view = frame
           .texture
           .create_view(&TextureViewDescriptor::default());

        let mut encoder = self
           .device
           .create_command_encoder(&CommandEncoderDescriptor::default());

        {
            let _render_pass = encoder.begin_render_pass(&RenderPassDescriptor {
                label: Some("Render Pass"),
                color_attachments: &[Some(RenderPassColorAttachment {
                    view: &view,
                    resolve_target: None,
                    ops: Operations {
                        load: LoadOp::Clear(Color::BLACK),
                        store: true,
                    },
                })],
                depth_stencil_attachment: None,
            });
        }

        self.queue.submit(std::iter::once(encoder.finish()));
        frame.present();
    }
}

Step 4: Implementing Physics Simulations

Our game engine will use rapier to handle physics simulations. We will create a new file called physics.rs in the src directory and add the following code:

use rapier::na::{Isometry3, Vector3};
use rapier::physics::{PhysicsEngine, RigidBody, RigidBodySet};

pub struct Physics {
    physics_engine: PhysicsEngine,
    rigid_body_set: RigidBodySet,
}

impl Physics {
    pub fn new() -> Self {
        let mut physics_engine = PhysicsEngine::new(Vector3::y_axis());
        let rigid_body_set = RigidBodySet::new();

        Physics {
            physics_engine,
            rigid_body_set,
        }
    }

    pub fn add_rigid_body(&mut self, position: Isometry3) {
        let rigid_body = RigidBody::new(position);
        self.rigid_body_set.insert(rigid_body);
    }

    pub fn simulate(&mut self) {
        self.physics_engine.step(&mut self.rigid_body_set);
    }
}

Step 5: Integrating the Window, Graphics, and Physics

Now that we have implemented the window, graphics, and physics, we need to integrate them. We will create a new file called main.rs in the src directory and add the following code:

use window::Window;
use renderer::Renderer;
use physics::Physics;

fn main() {
    let mut window = Window::new();
    let mut renderer = Renderer::new(&window);
    let mut physics = Physics::new();

    window.run();
    renderer.render();
    physics.simulate();
}

Step 6: Handling User Input

Our game engine needs to handle user input. We will add the following code to the window.rs file:

pub fn handle_input(&mut self) {
    for event in self.event_loop.poll_events() {
        match event {
            Event::WindowEvent { event,.. } => match event {
                WindowEvent::KeyboardInput {
                    input:
                        KeyboardInput {
                            virtual_keycode: Some(VirtualKeyCode::W),
                           ..
                        },
                   ..
                } => println!("W key pressed"),
                WindowEvent::KeyboardInput {
                    input:
                        KeyboardInput {
                            virtual_keycode: Some(VirtualKeyCode::S),
                           ..
                        },
                   ..
                } => println!("S key pressed"),
                _ => (),
            },
            _ => (),
        }
    }
}

Step 7: Adding Game Logic

Finally, we need to add game logic to our game engine. This will involve creating game objects, updating their positions, and handling collisions.

We will create a new file called game.rs in the src directory and add the following code:

use physics::Physics;
use renderer::Renderer;

pub struct Game {
    physics: Physics,
    renderer: Renderer,
}

impl Game {
    pub fn new() -> Self {
        let physics = Physics::new();
        let renderer = Renderer::new();

        Game { physics, renderer }
    }

    pub fn update(&mut self) {
        self.physics.simulate();
        self.renderer.render();
    }
}

We have now completed the 7 steps to writing a game engine in Rust. Our game engine can handle window management, graphics rendering, physics simulations, user input, and game logic.

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