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HTML

              
                <div id="start-screen">
  <h1>Slither Snake</h1>
  <div class="flexcontainer">
    <div class="row">
      <div class="instructions">
        <img src="https://res.cloudinary.com/dkw0kkkgd/image/upload/v1481315302/Arrow-keys_utpewf.jpg" height="60" width="92">
      </div>
      <div class="instructions">Use the arrow keys to change the snake's direction</div>
    </div>
    <div class="row">
      <div class="instructions">Don't run into your own tail</div>
      <div class="instructions">
        <img src="https://res.cloudinary.com/dkw0kkkgd/image/upload/v1481315307/Screen_Shot_2016-12-09_at_2.22.49_PM_f5yqz4.png" height="90" width="174">
      </div>
    </div>
    <div class="row">
      <div class="instructions">
        <img src="https://res.cloudinary.com/dkw0kkkgd/image/upload/v1481315311/Screen_Shot_2016-12-09_at_2.24.33_PM_ghqncx.png" height="90" width="190">
      </div>
      <div class="instructions">Don't run into the walls</div>
    </div>
    <div class="row">
      <div class="instructions">Eat the red dots to grow and increase your score</div>
      <div class="instructions">
        <img src="https://res.cloudinary.com/dkw0kkkgd/image/upload/v1481315317/Screen_Shot_2016-12-09_at_2.25.12_PM_xocpi7.png" height="40" width="48">
      </div>
    </div>
  </div>
  <button>Play</button>
</div>
              
            
!

CSS

              
                html {
  text-align: center;
}

canvas {
  margin-top: 10px;
  border: 1px solid gray;
}

.flexcontainer {
   display: -webkit-flex;
   display: flex;
   -webkit-flex-direction: column;
   flex-direction: column;
   width: 555px;
   margin: 0 auto;
   margin-top: 10px;
}

div {
  vertical-align: middle;
}

.instructions {
  display: inline-block;
  margin: 10px 20px;
  width: 200px;
}

.row:not(:last-child) {
  width: 100%;
  border-bottom: 1px solid lightgrey;
}

body,
h1 {
  margin: 0;
  padding: 0;
}

ul {
  list-style-type: none;
}

button {
  margin-top: 10px;
  cursor: pointer;
  font-size: 24px;
  padding: 10px 40px;
  border: none;
  border-radius: 5px;
}

button:hover {
  background: #A0A0A0;
}

#start-screen {
  font-family: 'Roboto', sans-serif;
  text-align: center;
  position: absolute;
  width: 100%;
  height: 100%;
  z-index: 99999;
  background: white;
}

h1 {
  background: #9999a1;
  padding: 5px;
  color: white;
}
              
            
!

JS

              
                var food;
var foodDiameter = 24;
var ghost;
var s;
var tailLength = 50;
var snakeSize = 32;
var gamePaused = true;
var highScore = 50;

if (localStorage.getItem("_highScore") === null) {
  localStorage._highScore = highScore;
}

function setup() {
  var iHeight = window.innerHeight <= 542 ? window.innerHeight - 20 : 522;
  var iWidth = window.innerWidth <= 957 ? window.innerWidth - 20 : 937;
  createCanvas(iWidth, iHeight);
  
  s = new Snake(width/4, height/2);
  // snake will chase an invisible ghost to steer
  ghost = new Ghost();
  pickLocation();
  var button = select('button');
  var startScreen = select('#start-screen');
  button.mouseClicked(function() {
    startScreen.hide();
    gamePaused = false;
  });
}

function draw() {
  background(245, 248, 250);
  noStroke();
  fill(54);
  textSize(16);
  text("tail length: " + tailLength, width/8, 30);
  text("high score: " + localStorage.getItem("_highScore"), width/8, 60);
  
  if (!gamePaused) {
    ghost.update();
    ghost.show();

    var ghostVect = createVector(ghost.x, ghost.y);

    if (s.eat(food)) {
      if (tailLength > localStorage.getItem("_highScore")) {
        localStorage._highScore = tailLength;
      }
      pickLocation();
    }

    // snake follows the ghost to steer
    s.seek(ghostVect);
    s.update();
    s.death();
  }
  s.display();
  
  fill(255, 0, 100);
  ellipse(food.x, food.y, foodDiameter, foodDiameter);

}

function pickLocation() {
  var offset = 40;
  food = createVector(random(offset, width - offset), random(offset, height - offset));
}

function keyPressed() {
  var ghostX = ghost.xspeed;
  var ghostY = ghost.yspeed;
  if (keyCode === UP_ARROW) {
    if (ghostY < 1) {
      ghost.dir(0, -1);
    }
  } else if (keyCode === DOWN_ARROW) {
    if (ghostY > -1) {
      ghost.dir(0, 1);
    }
  } else if (keyCode === RIGHT_ARROW) {
    if (ghostX > -1) {
      ghost.dir(1, 0);
    }
  } else if (keyCode === LEFT_ARROW) {
    if (ghostX < 1) {
      ghost.dir(-1, 0);
    }
  }
}

function Snake(x,y) {
  this.acceleration = createVector(0,0);
  this.velocity = createVector(0,0);
  this.position = createVector(x,y);
  this.r = snakeSize;
  this.maxspeed = 3;
  this.maxforce = 0.2;
  this.history = [];
  this.eatingVal = 0;

  // Method to update location
  this.update = function() {
        var v = createVector(this.position.x,this.position.y);
    this.history.push(v);
    
    if (this.history.length > tailLength) {
        this.history.splice(0,1);   
    }
    // Update velocity
    this.velocity.add(this.acceleration);
    // Limit speed
    this.velocity.limit(this.maxspeed);
    this.position.add(this.velocity);
    // Reset accelerationelertion to 0 each cycle
    this.acceleration.mult(0);
    
    if (this.eatingVal > 0) {
      this.eatingVal -= 0.5;
    }
  };

  this.applyForce = function(force) {
    // We could add mass here if we want A = F / M
    this.acceleration.add(force);
  };

  // A method that calculates a steering force towards a target
  // STEER = DESIRED MINUS VELOCITY
  this.seek = function(target) {

    var desired = p5.Vector.sub(target,this.position);  // A vector pointing from the location to the target

    // Scale to maximum speed
    desired.setMag(this.maxspeed);

    // Steering = Desired minus velocity
    var steer = p5.Vector.sub(desired,this.velocity);
    steer.limit(this.maxforce);  // Limit to maximum steering force

    this.applyForce(steer);
  };
  
  this.reset = function() {
    gamePaused = true;
    var that = this;
    this.history.forEach(function(seg) {
      seg.add(random(-10, 10), random(-10, 10));
    });
    setTimeout(function() {
      tailLength = 50;
      that.history = [];
      that.position = createVector(width/2, height/2);
      gamePaused = false;
    }, 3000);
  }
  
  this.death = function() {
    var offset = this.r/2;
    var outOfBoundsX = this.position.x < offset || this.position.x > width - offset;
    var outOfBoundsY = this.position.y < offset || this.position.y > height - offset;
    if (outOfBoundsX || outOfBoundsY) {
      this.reset();
    } else {
      for (var i = 0; i < this.history.length - 10; i++) {
        var pos = this.history[i];
        var d = dist(this.position.x, this.position.y, pos.x, pos.y);
        if (d < 2) {
          this.reset();
        }
      }
    }
  }
  
  this.eat = function(pos) {
    var d = dist(this.position.x, this.position.y, pos.x, pos.y);
    if (d < foodDiameter) {
      tailLength += 20;
      this.eatingVal = 20;
      return true;
    } else {
      return false;
    }
  }

  this.display = function() {
    // Draw a snake rotated in the direction of velocity
    var theta = this.velocity.heading() + PI/2;
    fill(0,150,150);
    noStroke();
    for (var i = 0; i < this.history.length; i++) {
      var pos = this.history[i];
      var size = map(i,0,this.history.length,5,this.r);
      ellipse(pos.x, pos.y, size, size);
    } 
    fill(0,150,150);
    ellipse(this.x,this.y,this.r,this.r);
    push();
    translate(this.position.x,this.position.y);
    rotate(theta);
    fill(0,210,150);
    ellipse(0, -this.eatingVal, this.r, this.r);
    fill(255, 0, 0);
    rect(-2, -2 * this.eatingVal, 4, 15);
    stroke(0);
    fill(255);
    triangle(-10, -20, -10, 0, 0, 0);
    triangle(10, -20, 10, 0, 0, 0);
    fill(0,150,150);
    noStroke();
    ellipse(0, 0, this.r, this.r);
    if (!gamePaused) {
      fill(255);
      ellipse(-this.r/5, 0, 12, 12);
      ellipse(this.r/5, 0, 12, 12);
      fill(98);
      ellipse(-this.r/5, 0, 6, 6);
      ellipse(this.r/5, 0, 6, 6);
    } else {
      fill(255);
      textSize(12);
      text("X", -this.r/4 - 1, 0);
      text("X", 1, 0);
    }
    pop();
  };
}

function Ghost() {
  this.x = 0;
  this.y = width/2;
  this.xspeed = 5;
  this.yspeed = 0;

  this.dir = function(x, y) {
    this.xspeed = x * 5;
    this.yspeed = y * 5;
  }

  this.update = function() {

    this.x = this.x + this.xspeed;
    this.y = this.y + this.yspeed;

    this.x = constrain(this.x, 0, width - 20);
    this.y = constrain(this.y, 0, height - 20);
  }

  this.show = function() {
    fill(255, 0);
    noStroke();
    rect(this.x, this.y, 20, 20);
  }
}
              
            
!
999px

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