JavaScript p5.js：对象对齐

Question

Hi I'm creating a snake game right now and I have a problem that my food is not aligned with my snake so I can't get my snake to eat it, no error messsages just can't get that working, please explain where I went wrong and how I can get this to be aligned and eaten.

Here is my code:

My Food:

function columns()
{
  return floor(width / scl);
}

function rows()
{
  return floor(height / scl);
}

function randomPlaceFood()
{
  return createVector(floor(random(columns())), floor(random(rows())));
}

function Food()
{
  this.vector = randomPlaceFood().mult(scl);

  this.x = random(0, 700);
  this.y = random(0, 700);

  this.updateFood = function()
  {
    this.vector = randomPlaceFood().mult(scl);
  }

  this.showFood = function()
  {
    fill(255, 0, 10);
    rect(this.x, this.y, scl, scl);
  }

}

My Snake:

function Snake()
{
  this.x = 0;
  this.y = 0;

  this.xspeed = 0;
  this.yspeed = 0;

  this.updateSnake = function()
  {
    this.x = this.x + this.xspeed * scl;
    this.y = this.y + this.yspeed * scl;

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

  this.showSnake = function()
  {
    fill(255);
    rect(this.x, this.y, scl, scl);
  }

  this.direction = function(x, y)
  {
    this.xspeed = x;
    this.yspeed = y;
  }

  this.eatFood = function()
  {
     if (this.x === food.x && this.y === food.y)
     {
       randomPlaceFood();
     }else
     {
       randomPlaceFood();
     }
  }

  this.keyPressed = function()
  {
    if (keyCode === 87)
    {
      snake.direction(0, -1);
    } else if (keyCode === 83)
    {
      snake.direction(0, 1);
    } else if (keyCode === 68)
    {
      snake.direction(1, 0);
    } else if (keyCode === 65)
    {
      snake.direction(-1, 0);
    }
  }
}

And the main file:

var snake;

var scl = 20;
var food;


function setup()
{
  //Sets the Canvas
  createCanvas(700, 700);

  //Creates a new object using the variable snake
  snake = new Snake();

  food = new Food();

  frameRate(10);

}

function draw()
{
  //Sets the Background, number implies the colour
  background(40);

  //Adds all the values set within the function to the snake
  snake.updateSnake();
  snake.showSnake();
  snake.keyPressed();

  food.showFood();
  food.updateFood();

  if(snake.eatFood())
  {
    randomPlaceFood();
  }
}

Answer 1

Check out this line:

if (this.x === food.x && this.y === food.y)

You're only checking whether the snake is perfectly aligned with the food. Like you've found out, this almost never happens, because it requires pixel-perfect precision.

Instead, you want to detect whether the snake is colliding with the food. You do this using collision detection. Google is your friend, but the general algorithm for checking two rectangles is this:

if(rectOneRight > rectTwoLeft && rectOneLeft < rectTwoRight && rectOneBottom > rectTwoTop && rectOneTop < rectTwoBottom){
  //rectangles are colliding
}

Shameless self-promotion: I wrote a tutorial on collision detection available here . It's for Processing, but everything is the same in P5.js.