The Donuts Code

The spinning “donuts” that has brought some attention recently and was created by the amazing Andy Sloane. No wonder, a flying donut on your terminal? You can find the code below in c. The “pixels” are ASCII characters .,-~:;=!*#$@ that accounts for the illumination value of the surface, but I’ll explain step by step below along with the math.

Mission:

Steps

1. Create a circle of radius R2 centered at R2
2. Create a torus(‘donuts’) which rotates on the Y axis
3. Now, we need to rotate about the X and Z axis so it looks like it’s floating and spinning on the screen. Basically, a flying donut. Why not?
4. Well, how to map this 3D objet into 2D ie terminal screen?

Each character in the code corresponds to a pixel on our terminal. However, how to shade it? For this, we calculate the dot product of the surface normal and the direction of the light. This will say how light and how dark will look on the screen.

The output of the dot product will be:

5. Finally, you map the result of the dot product (step 4) to these characters to tweak the lighting. That’s it!
   

Code

#include <stdio.h>
#include <math.h>
#include <string.h>
#include <unistd.h>

int main() {
    float A = 0, B = 0;
    float i, j;
    int k;
    float z[1760];
    char b[1760];
    printf("\x1b[2J");
    for(;;) {
        memset(b,32,1760);
        memset(z,0,7040);
        for(j=0; j < 6.28; j += 0.07) {
            for(i=0; i < 6.28; i += 0.02) {
                float c = sin(i);
                float d = cos(j);
                float e = sin(A);
                float f = sin(j);
                float g = cos(A);
                float h = d + 2;
                float D = 1 / (c * h * e + f * g + 5);
                float l = cos(i);
                float m = cos(B);
                float n = sin(B);
                float t = c * h * g - f * e;
                int x = 40 + 30 * D * (l * h * m - t * n);
                int y= 12 + 15 * D * (l * h * n + t * m);
                int o = x + 80 * y;
                int N = 8 * ((f * e - c * d * g) * m - c * d * e - f * g - l * d * n);
                if(22 > y && y > 0 && x > 0 && 80 > x && D > z[o]) {
                    z[o] = D;
                    b[o] = ".,-~:;=!*#$@"[N > 0 ? N : 0];
                }
            }
        }
        printf("\x1b[H");
        for(k = 0; k < 1761; k++) {
            putchar(k % 80 ? b[k] : 10);
            A += 0.00004;
            B += 0.00002;
        }
        usleep(30000);
    }
    return 0;
}

Credits

• Check out Andy Sloane blog post for more details about the math: Blog Post: “Donut math: how donut.c works” blog post by Andy Sloane
• Checkout Alex Friedman for a quick explanation and code: Donut-shaped C code that generates a 3D spinning donut