Creating a Doom-style 3D engine in C [video]

In the early 1990s, id Software revolutionized the gaming industry with the release of Doom, a groundbreaking first-person shooter that set the standard for 3D graphics in games. The game’s 3D engine, developed by John Carmack, was a marvel of its time, allowing for fast and smooth rendering of 3D environments. In this article, we’ll explore how to create a Doom-style 3D engine in C, a programming language that was instrumental in the development of the original Doom.

Why C?

C is a natural choice for building a 3D engine, especially one inspired by Doom. The language’s low-level memory management, performance, and flexibility make it an ideal candidate for building high-performance graphics engines. Additionally, C’s simplicity and portability ensure that the engine can be easily compiled and run on a variety of platforms.

The Basics of 3D Graphics

Before diving into the implementation, it’s essential to understand the basics of 3D graphics. In a 3D engine, the following components are crucial:

1. Vertex Buffer: A collection of 3D vertices that define the shape of objects in the scene.
2. Transformation Matrix: A mathematical representation of the camera’s position, orientation, and perspective.
3. Projection Matrix: A matrix that converts 3D coordinates to 2D screen coordinates.
4. Rendering Loop: A loop that iterates through the vertex buffer, applying transformations and projections to render the scene.

Implementing the 3D Engine

To create a Doom-style 3D engine in C, we’ll focus on the following components:

 1. Vertex Buffer

We’ll represent each vertex as a struct containing its 3D coordinates (x, y, z) and a color value:
“`c
typedef struct {
float x, y, z;
unsigned char r, g, b;
} Vertex;
“`
 2. Transformation Matrix

We’ll use a 4×4 matrix to represent the camera’s transformation:
“`c
typedef struct {
float m[4][4];
} Matrix;
“`
 3. Projection Matrix

We’ll use a similar 4×4 matrix to represent the projection:
“`c
Matrix projection_matrix;
“`
 4. Rendering Loop

The rendering loop will iterate through the vertex buffer, applying transformations and projections to render the scene:
“`c
void render_scene(Vertex vertices, int num_vertices) {
for (int i = 0; i < num_vertices; i++) {
Vertex v = vertices[i];
// Apply transformation matrix
v.x = v.x  transformation_matrix.m[0][0] + v.y  transformation_matrix.m[0][1] + v.z  transformation_matrix.m[0][2] + transformation_matrix.m[0][3];
v.y = v.x  transformation_matrix.m[1][0] + v.y  transformation_matrix.m[1][1] + v.z  transformation_matrix.m[1][2] + transformation_matrix.m[1][3];
v.z = v.x  transformation_matrix.m[2][0] + v.y  transformation_matrix.m[2][1] + v.z  transformation_matrix.m[2][2] + transformation_matrix.m[2][3];

// Apply projection matrix
v.x = v.x  projection_matrix.m[0][0] + v.y  projection_matrix.m[0][1] + v.z  projection_matrix.m[0][2] + projection_matrix.m[0][3];
v.y = v.x  projection_matrix.m[1][0] + v.y  projection_matrix.m[1][1] + v.z  projection_matrix.m[1][2] + projection_matrix.m[1][3];

// Render vertex
// …
}
}
“`
Putting it all Together

With the basic components in place, we can now create a simple 3D engine that renders a Doom-style scene. Here’s a sample implementation:
“`c
int main() {
// Initialize vertex buffer
Vertex vertices[] = {
{-1, -1, 0, 255, 0, 0}, // Red vertex
{1, -1, 0, 0, 255, 0}, // Green vertex
{0, 1, 0, 0, 0, 255} // Blue vertex
};
int num_vertices = sizeof(vertices) / sizeof(Vertex);

// Initialize transformation matrix
Matrix transformation_matrix;
transformation_matrix.m[0][0] = 1; transformation_matrix.m[0][1] = 0; transformation_matrix.m[0][2] = 0; transformation_matrix.m[0][3] = 0;
transformation_matrix.m[1][0] = 0; transformation_matrix.m[1][1] = 1; transformation_matrix.m[1][2] = 0; transformation_matrix.m[1][3] = 0;
transformation_matrix.m[2][0] = 0; transformation_matrix.m[2][1] = 0; transformation_matrix.m[2][2] = 1; transformation_matrix.m[2][3] = 0;
transformation_matrix.m[3][0] = 0; transformation_matrix.m[3][1] = 0; transformation_matrix.m[3][2] = 0; transformation_matrix.m[3][3] = 1;

// Initialize projection matrix
Matrix projection_matrix;
projection_matrix.m[0][0] = 1; projection_matrix.m[0][1] = 0; projection_matrix.m[0][2] = 0; projection_matrix.m[0][3] = 0;
projection_matrix.m[1][0] = 0; projection_matrix.m[1][1] = 1; projection_matrix.m[1][2] = 0; projection_matrix.m[1][3] = 0;
projection_matrix.m[2][0] = 0; projection_matrix.m[2][1] = 0; projection_matrix.m[2][2] = 1; projection_matrix.m[2][3] = 0;
projection_matrix.m[3][0] = 0; projection_matrix.m[3][1] = 0; projection_matrix.m[3][2] = 0; projection_matrix.m[3][3] = 1;

// Render scene
render_scene(vertices, num_vertices);

return 0;
}
“`
Conclusion

In this article, we’ve explored the basics of creating a Doom-style 3D engine in C. By implementing a vertex buffer, transformation matrix, projection matrix, and rendering loop, we’ve created a simple 3D engine that renders a scene. While this implementation is far from the complexity of the original Doom engine, it demonstrates the fundamental principles of 3D graphics programming.

Video Tutorial

For a more in-depth look at implementing a Doom-style 3D engine in C, check out the accompanying video tutorial:

[Insert video link]

In the video, we’ll cover the implementation in more detail, including how to optimize the engine for performance and add additional features such as texture mapping and lighting.