arthurbricq/gameengine

A 3D game engine, written fully from scratch in Rust, to display and move within a 3D world as if seen from a camera.

Custom 3D Game Engine in Rust

A 3D game engine, written from scratch (without OpenGL, Vulkan or anything else) in Rust. The only library that I used is pixels crate, that allows to draw RGBA pixels on the screen. I implemented manually all the 3D-to-2D algorithms and optimized polygon operations to be able to render a realistic world.

It features:

• 3D to 2D projections: to represent a 3D world as a 2D buffer of pixels, through a realistic camera model.
• Different rendering algorithm have been implementing:
  • A basic raytracing: this was my first POC, it's slow (1000 polygons render at ~5 FPS)
  • A more complex one: the Painter algorithm : 1000 polygons are rendered at 60 FPS !
• In my quest of optimizing, I implemented a Binary-Space-Partitioning representation of the space, to make the painter algorithm about twice faster.
• Textures rendering are also implemented. User-defines textures are loaded when opening the world and used as static variables elsewhere in the code.
• User motions in the 3D world

cargo run --release

Here's a small example with a few hundreds polygon displayed.

And here's an example of texture rendering

Using textures, it gets easy to "tune" your own world. For instance, I was able to render minecraft like cubes, as seen here.

Such kind of world is created with a quick API. For instance, you'd use the following three lines to create 3 blocks:

world.add_cube(Cube3::minecraft_like(Vector3::newi(0,0,0), soil_side, soil_top));
world.add_cube(Cube3::minecraft_like(Vector3::newi(0,-1,0), wood, wood));
world.add_cube(Cube3::minecraft_like(Vector3::newi(1,-3,0), stone, stone));

The BSP polygon splitting that occurs during the construction of the BSP plane allows to create more complex shapes with occlusion. For instance, adding a continuous floor.

Why have I done this ?

I wanted to learn more about computer graphics, algorithmic in general, in software architecture and to keep progressing in Rust.

As a matter of fact, writing your own game engine involves a lot of design questions, of algorithms implementation and of writing somewhat optimal code.

What was my goal ?

This seems to be one of my biggest personal project, I'd love to keep expanding it to an actual playable game.

I would like to implement a small game, either a version of Doom, or a minimal version of Minecraft.

How to change screen resolution ?

Change the global constants WIDTH and HEIGHT in main.rs.

How to change the camera model ?

In the file camera.rs, you can change the ::default() constructor to change the camera's focal distance or its optical center.

Personal TODO-list

Last steps to have a something more usable (if I ever find the time to !)

• obstacle detection: block motion when hitting a face
• format to load a map

Notes

Project a 3D world into a camera

What is a camera?

A basic camera model consists of

• Projective transformation is any mapping of points that preserves straight lines
• A camera is a mapping between the 3D world (image space) and a 2D image: a matrix

Projection from world coordinate to camera coordinates

Let a point $x = [x,y,z]$ expressed in the world coordinate. The homogenous transformation $T$ such that the same point is expressed in camera coordinates $X = [X,Y,Z]$ is given by $X' = T x'$ (where $x'$ denotes the homogeneous coordinates), and $T = [R, t]$.

To express the rotation matrix $R$, one can simply write $R = [r1, r2, r3]$ where $r_i$ is the world's i-th axis expressed in camera coordinates.