ASCII Donut Spinner in C

A terminal-based 3D ASCII donut animation written in C.

This program renders a rotating torus (donut) directly inside the terminal using mathematical projection, trigonometry, depth buffering, and ASCII shading techniques.

The animation continuously rotates in real-time and simulates 3D lighting entirely using text characters.

This project focuses on learning:

• terminal rendering
• 3D projection math
• trigonometry in graphics
• depth buffering
• animation loops
• low-level rendering concepts in C

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Features

• Real-time rotating ASCII donut
• 3D perspective projection
• Depth buffer (Z-buffer) implementation
• ASCII lighting and shading
• Pure terminal rendering
• Written entirely in C
• Uses trigonometric functions for rotation

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How It Works

The program mathematically generates points on a torus surface and projects them onto a 2D terminal screen.

For every frame:

• Clears previous frame buffer
• Calculates 3D donut coordinates
• Applies rotation transformations
• Projects 3D points into 2D screen space
• Computes brightness/shading
• Uses ASCII characters as pixels
• Prints updated frame to terminal

The animation repeats continuously to create smooth rotation.

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Tutorial / Rendering Pipeline

1. Create Screen Buffers

Two buffers are created:

char b[1760];
float z[1760];

• b[] stores ASCII characters
• z[] stores depth values (Z-buffer)

This allows proper 3D overlap rendering.

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2. Generate Donut Surface Points

Nested loops generate points across the torus surface:

for (j = 0; j < 6.28; j += 0.07)
for (i = 0; i < 6.28; i += 0.02)

These loops iterate across circular angles using radians.

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3. Apply Rotation

Rotation variables:

A += 0.04;
B += 0.02;

control donut rotation over time.

Trigonometric functions:

sin()
cos()

are used to rotate 3D coordinates.

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4. Project 3D → 2D

Perspective projection converts 3D points into terminal coordinates:

int x = 40 + 30 * D * (...);
int y = 12 + 15 * D * (...);

This creates the illusion of depth.

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5. Depth Buffering (Z-buffer)

if (D > z[o])

ensures closer points overwrite farther points.

This prevents rendering artifacts.

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6. ASCII Shading

Brightness values are mapped to characters:

".,-~:;=!*#$@"

Different characters simulate lighting intensity.

Example:

.  -> dark
@  -> brightest

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7. Terminal Rendering

The frame is drawn using:

putchar()

and terminal cursor reset escape sequences:

printf("\x1b[H");

This redraws frames in-place to create animation.

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Build

Compile using:

gcc donut.c -o donut -lm

The -lm flag links the math library.

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Run

./donut

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Example Output

              @$@@$@@
          $$$$$$$$$$$$$
       $$$$############$$$
     $$$####********####$$$
    $$###****!!!!!****###$$

(The actual donut rotates continuously in terminal.)

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Concepts Practiced

• 3D coordinate systems
• Perspective projection
• Rotation matrices
• Trigonometry in graphics
• ASCII rendering
• Frame buffering
• Z-buffering
• Animation loops
• Terminal graphics
• Real-time rendering

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Dependencies

Standard C libraries only:

• stdio.h
• math.h
• string.h
• unistd.h

No graphics engine required.

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Inspiration

Inspired by the classic ASCII donut demo created by Andy Sloane.

A legendary demonstration of how powerful math and low-level rendering can be even inside a terminal.