The beginning of my journey: making a rendering engine

#gamedev #cpp

Nota Bene: This serie of articles is mainly focused on my experience while making Voksel, a 3D game made in a Minecraft style, so I will only write about my opinion and how I solve the problems I met !

A month ago, I got this strange idea after having taught myself on OpenGL : What if I made my own rendering engine? It could be funny, and I could learn a lot ! That's how I started making Zavtrak. Few days after, another idea hit me: what if I made my own version of Minecraft using this engine ? So that's how my journey started, on a sunny day of September !

I made a small ToDo to know where I was going :

abstraction code for :
- VAO, VBO, EBO
- shaders
- free fly camera
- window creation

(my goal was, and still is, to create a 3D rendering library acting as a nearly 0 cost abstraction for OpenGL)

A VAO acts an array storing vertex (a collection of data per 3D point) attribute pointers, used by OpenGL when given a VBO (vertex buffer object, storing vertices) to know if it looking at a position, a color, a texture coordinate... in a given vertex.

An EBO (element buffer object) is an array storing indexes of vertices (stored in a given VBO) to "link" them :

vertices = [
    # position      # color
    [0.0, 0.0, 0.0, 1.0, 0.5, 0.0],
    [0.0, 1.0, 0.0, 0.0, 0.5, 1.0],
    [1.0, 0.0, 0.0, 0.5, 1.0, 0.5]
]
elements = [
    0, 1, 2
]

defines a right-angle triangle (when giving the data to OpenGL). An EBO avoids repeting the same vertex multiple times, which can be pretty heavy when giving a lot of vertices to the GPU, by only defining the index of the element to use.

A shader is a small program (written in GLSL) to tell OpenGL how to draw a single pixel, given a vertex.

My idea was to have something like this :

auto shader = zk::Shader("shader.vert", "shader.frag");

zk::Vertices vertices({
    // positions         // colors
     0.5f, -0.5f, 0.0f,  1.0f, 0.0f, 0.0f,   // bottom right
    -0.5f, -0.5f, 0.0f,  0.0f, 1.0f, 0.0f,   // bottom left
     0.0f,  0.5f, 0.0f,  0.0f, 0.0f, 1.0f    // top 
});
zk::objects::VertexArray VAO;
zk::objects::VertexBuffer VBO;
// bind the Vertex Array Object first, then bind and set vertex buffer(s)
// and then configure vertex attributes(s).
VAO.bind();
VBO.setData(vertices);
zk::objects::setVertexAttrib(0, 3, 6, 0);
zk::objects::setVertexAttrib(1, 3, 6, 3);

shader.use();
// do drawing...

which is basically the same thing as this (without the window configuration and all, which you can find here), a lot shorter and easier to understand, uh ?

The biggest problem I have now is that we must configure everything ourself (setting vertex attributes, and creating a VAO and a VBO, binding them...) (and I still didn't fix it, since I wanted to focus on the game and rewrite the engine later).

After writing a lot of redundant code, I could start writing a small game with it (you can find my experimentations here). My biggest struggle when I started writing the game was the vertex attributes (as you can see on the cover image, I messed up my vertex attributes and OpenGL handled it as if everything was fine).

This concludes the first article of this serie, which is more a "explain-me-the-plot" article than a "the-problems-of-writing-a-rendering-engine", but if you want to know my pros and cons of making your own, here they are :

Pros

you control everything
you can give it the interface you want (I mean, not graphically but programmatically)
you understand how it works under the hood

Cons

writing your own rendering engine is really hard (I made a very simple one since Zavtrak acts as an abstraction layer for OpenGL)
it can take a lot of time (and headaches !)

I will now explain briefly the purpose of this video game I am making, Voksel.

As I said, it is a 3D exploration game made in a Minecraft style, where the player can explore a procedurally generated world made of voxel (3D pixels). The goal behind this project is to create a game in the same spirit as Proteus: an audio-visual exploration game, but with something more: helping the players to relax.

P.S.: I wrote this article in one go, only keeping in mind "how could I introduce you to the problems we met when creating a game", so it can be quite disjointed, I am sorry about that

Top comments (8)

Vijay Koushik, S. 👨🏽‍💻 • Oct 8 '18

This is a great awareness article for people like me who think "you know what? I think I can do this without a library / framework".
But when I read "rectangular triangle", I was like wait what? 🤨