snake.js

// Author: Huahua (https://www.youtube.com/user/xxfflower)
// p5 web editor: https://editor.p5js.org
var rows = 25;
var cols = 25;
var a = 20;
var s;
var f;

function Snake() {
  this.x = 12;
  this.y = 12;
  this.sx = 0;
  this.sy = 0;
  this.body = [[this.x, this.y]];
  this.ss = 1;
  
  this.dead = false;
  
  this.isDead = function() {
    return this.dead;
  }
  
  this.len = function() {
    return this.body.length;
  }
  
  this.update = function() {
    this.x = constrain(this.x + this.sx, -1, cols);
    this.y = constrain(this.y + this.sy, -1, rows);
    
    if (this.x < 0 || this.y < 0 || this.x == cols || this.y == rows) {      
      this.dead = true;
      return;
    }
    
    if (this.contains(createVector(this.x, this.y), 3)) {      
      this.dead = true;
      return;
    }
        
    this.body.pop();
    this.body.unshift([this.x, this.y]);    
  }
  
  this.dir = function(dx, dy) {
    if (this.len() > 1) {
      if (dx !== 0 && dx === -this.sx ||
          dy !== 0 && dy === -this.sy) return;
    }
    this.sx = dx;
    this.sy = dy;
  }
  
  this.draw = function() {
    fill(255);
    for (var i = 1; i < this.body.length; ++i) {
      rect(this.body[i][0] * a, this.body[i][1] * a, a, a);
    }
    fill(0, 0, 255);
    rect(this.body[0][0] * a, this.body[0][1] * a, a, a);
  }
  
  this.canEat = function(v) {
    return (this.x === v.x && this.y === v.y);
  }
  
  this.eat = function() {
    this.body.push([this.x, this.y]);
  }
  
  this.contains = function(v, s) {
    for (var i = s || 0; i < this.body.length; ++i) {
      if (this.body[i][0] === v.x &&
          this.body[i][1] === v.y) return true;
    }
    return false;
  }
}

function setup() {
  createCanvas(cols * a, rows * a);
  frameRate(10);
  s = new Snake();
  generateFood();
}

function draw() { 
  background(30); 
  
  if (!s.isDead()) {
    s.update();
    if (s.canEat(f)) {
      s.eat(f);
      generateFood();
    }
    
    frameRate(10 + s.len() / 2);
  } 
  
  s.draw();
  
  fill(255, 0, 0);
  rect(f.x * a, f.y * a, a, a);
  
  if (s.isDead()){    
    textSize(32);
    textAlign(CENTER);
    fill(255, 0, 255);
    text('Game Over!', cols * a / 2, rows * a /2);
    textSize(16);
    fill(255, 255, 0);
    text('Press enter to restart', cols * a / 2, rows * a / 2 + 2 * a);
  } 
}

function generateFood() {
  while (true) {
    f = createVector(floor(random()*cols), floor(random()*rows));
    if (!s.contains(f)) break;
  }
}

function keyPressed() {  
  if (keyCode === LEFT_ARROW) {
    s.dir(-1, 0);
  } else if (keyCode == RIGHT_ARROW) {
    s.dir(1, 0);
  } else if (keyCode == UP_ARROW) {
    s.dir(0, -1);
  } else if (keyCode == DOWN_ARROW) {
    s.dir(0, 1);
  } else if (keyCode == ENTER) {
    if (s.isDead()) {
      setup();
    }
  }
}