ASCII snake in C

17 Nov, 2024

Introduction

I've got some small/tiny gamedev projects on my pocket that I haven't documented here in my Bearblog account. The first one is an ASCII Snake game only using the curses library. There will be another similar post on making Snake game using Raylib.

#1 Libraries

#include <curses.h>
#include <stdbool.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <string.h>

#2 Consts, structs and global vars

#define MAX_SCORE 256
#define FRAME_TIME 180000

typedef struct {
    int x;
    int y;
} Vec2;

int score = 0;
char score_message[32];

bool skip = false;
bool is_running = true;

int screen_width = 25;
int screen_height = 20;

// initialize screen
WINDOW *win;

// snake
Vec2 head = {0, 0};
Vec2 segments[MAX_SCORE + 1];
Vec2 dir = {1, 0};

// berry
Vec2 berry;

#3 Function declaration

void game_over();
void init();
void quit_game();
void restart_game();
bool collide(Vec2 a, Vec2 b);
bool collide_snake_body(Vec2 point);
Vec2 spawn_berry();
void process_input();
void draw_border(int y, int x, int width, int height);
void draw();
void update();
void game_over();

#4 Collision: the collide function

collide: Checks if two points have the same coordinates.
collide_snake_body: Checks if a point collides with the snake's body.

bool collide(Vec2 a, Vec2 b) 
{
    if (a.x == b.x && a.y == b.y) {
        return true;
    }
    else return false;
}

bool collide_snake_body(Vec2 point) 
{
    for (int i = 0; i < score; i++) {
        if (collide(point, segments[i])) {
            return true;
        }
    }
    return false;
}

#5 Spawning berries

Generates a random position for a "berry" on the screen, ensuring it's not on the snake's head or body, and has a 1-pixel padding from the edges

Vec2 spawn_berry() 
{
    // spawn a new berry with 1 pixel padding from edges and not inside of the snake
    Vec2 berry = { 1 + rand() % (screen_width - 2), 1 + rand() % (screen_height - 2) };
    while (collide(head, berry) || collide_snake_body(berry)) {
        berry.x = 1 + rand() % (screen_width - 2);
        berry.y = 1 + rand() % (screen_height - 2);
    }
    return berry;
}

#6 Game Area: draw border

Draws a border on the screen using ASCII characters, with specified width and height, using ncurses library functions.

void draw_border(int y, int x, int width, int height) 
{
    // top row
    mvaddch(y, x, ACS_ULCORNER);
    mvaddch(y, x + width * 2 + 1, ACS_URCORNER);
    for (int i = 1; i < width * 2 + 1; i++) {
        mvaddch(y, x + i, ACS_HLINE);
    }
    // vertical lines
    for (int i = 1; i < height + 1; i++) {
        mvaddch(y + i, x, ACS_VLINE);
        mvaddch(y + i, x + width * 2 + 1, ACS_VLINE);
    }
    // bottom row
    mvaddch(y + height + 1, x, ACS_LLCORNER);
    mvaddch(y + height + 1, x + width * 2 + 1, ACS_LRCORNER);
    for (int i = 1; i < width * 2 + 1; i++) {
        mvaddch(y + height + 1, x + i, ACS_HLINE);
    }
}

#7 Quit and Restart

quit_game: Exits the game cleanly, restoring the terminal state.
restart_game: Resets game state to initial values.

void quit_game() 
{
    // exit cleanly from application
    endwin();
    // clear screen, place cursor on top, and un-hide cursor
    printf("\e[1;1H\e[2J");
    printf("\e[?25h");

    exit(0);
}

void restart_game() 
{
    head.x = 0;
    head.y = 0;
    dir.x = 1;
    dir.y = 0;
    score = 0;
    sprintf(score_message, "[ Score: %d ]", score);
    is_running = true;
}

#8 Init function

This code initializes the game by:

Seeding the random number generator
Setting up the terminal window with ncurses
Initializing colors and color pairs
Randomly placing the "berry" on the screen
Initializing the score message

void init() 
{
    srand(time(NULL));
    // initialize window
    win = initscr();
    // take player input and hide cursor
    keypad(win, true);
    noecho();
    nodelay(win, true);
    curs_set(0);

    // initialize color
    if (has_colors() == FALSE) {
        endwin();
        fprintf(stderr, "Your terminal does not support color\n");
        exit(1);
    }
    start_color();
    use_default_colors();
    init_pair(1, COLOR_BLUE, -1);
    init_pair(2, COLOR_GREEN, -1);
    init_pair(3, COLOR_YELLOW, -1);


    berry.x = rand() % screen_width;
    berry.y = rand() % screen_height;

    // update score message
    sprintf(score_message, "[ Score: %d ]", score);
}

#9 Game Over state

game_over: Displays a "Game Over" message and waits for user input to restart or quit.

void game_over() 
{
    while (is_running == false) {
        process_input();

        mvaddstr(screen_height / 2, screen_width - 16, "              Game Over          ");
        mvaddstr(screen_height / 2 + 1, screen_width - 16, "[SPACE] to restart, [ESC] to quit ");
        attron(COLOR_PAIR(3));
        draw_border(screen_height / 2 - 1, screen_width - 17, 17, 2);
        attroff(COLOR_PAIR(3));

        usleep(FRAME_TIME);
    }
}

#10 Movement - process_input

This code processes user input by:

Reading a key press from the terminal window
Updating the snake's direction based on arrow key presses
Preventing the snake from reversing direction immediately
Restarting the game when the space bar is pressed
Quitting the game when the escape key is pressed

void process_input() 
{
    int pressed = wgetch(win);
    if (pressed == KEY_LEFT) {
        if (dir.x == 1) {
            return;
            skip = true;
        }
        dir.x = -1;
        dir.y = 0;
    }
    if (pressed == KEY_RIGHT) {
        if (dir.x == -1) {
            return;
            skip = true;
        }
        dir.x = 1;
        dir.y = 0;
    }
    if (pressed == KEY_UP) {
        if (dir.y == 1) {
            return;
            skip = true;
        }
        dir.x = 0;
        dir.y = -1;
    }
    if (pressed == KEY_DOWN) {
        if (dir.y == -1) {
            return;
            skip = true;
        }
        dir.x = 0;
        dir.y = 1;
    }
    if (pressed == ' ') {
        if (!is_running)
            restart_game();
    }
    if (pressed == '\e') {
        is_running = false;
        quit_game();
    }
}

#11 Update game state and Draw function

update:

Updates the snake's segments and position
Checks for collisions with the body or walls
Handles eating a berry and updates the score
Waits for a short time to control the game's frame rate

draw:

Clears the screen and redraws the game elements
Draws the berry, snake, and border using different colors
Displays the score message

void update() 
{
    // update snake segments
    for (int i = score; i > 0; i--) {
        segments[i] = segments[i - 1];
    }
    segments[0] = head;

    // move snake
    head.x += dir.x;
    head.y += dir.y;

    // collide with body or walls
    if (collide_snake_body(head) || head.x < 0 || head.y < 0 \
            || head.x >= screen_width || head.y >= screen_height) {
        is_running = false;
        game_over();
    }

    // eating a berry
    if (collide(head, berry)) {
        if (score < MAX_SCORE) {
            score += 1;
            sprintf(score_message, "[ Score: %d ]", score);
        }
        else {
            // WIN!
            printf("You Win!");
        }
        berry = spawn_berry();
    }

    usleep(FRAME_TIME);
}

void draw() 
{
    erase();

    attron(COLOR_PAIR(1));
    mvaddch(berry.y+1, berry.x * 2+1, '@');
    attroff(COLOR_PAIR(1));

    // draw snake
    attron(COLOR_PAIR(2));
    for (int i = 0; i < score; i++) {
        mvaddch(segments[i].y+1, segments[i].x * 2 + 1, ACS_DIAMOND);
    }
    mvaddch(head.y+1, head.x * 2+1, 'O');
    attroff(COLOR_PAIR(2));

    attron(COLOR_PAIR(3));
    draw_border(0, 0, screen_width, screen_height);
    attroff(COLOR_PAIR(3));
    mvaddstr(0, screen_width - 5, score_message);
}

#12 Main

This code is the main entry point of the game:

Processes command-line arguments to set the screen dimensions
Initializes the game state

int main(int argc, char *argv[])
{
    // process user args
    if (argc == 1) {}
    else if (argc == 3) {
        if (!strcmp(argv[1], "-d")) {
            if (sscanf(argv[2], "%dx%d", &screen_width, &screen_height) != 2) {
                printf("Usage: snake [options]\nOptions:\n -d [width]x[height]"
                       "\tdefine dimensions of the screen\n\nDefault dimensions are 25x20\n");
                exit(1);
            }
        }
    }
    else {
        printf("Usage: snake [options]\nOptions:\n -d [width]x[height]"
               "\tdefine dimensions of the screen\n\nDefault dimensions are 25x20\n");
        exit(1);
    }

    init();
    while(true) {        
        process_input();
        if (skip == true) {
            skip = false;
            continue;
        }
        // ---------- update ----------
        update();

        // ------------ draw ------------
        draw();
    }
    quit_game();

    return 0;
}

Result

c-snake-ascii