Lesson 11

Let's make it so an apple appears on the screen!

var draw = function(snakeToDraw, apple) {
  var drawableSnake = { color: "green", pixels: snakeToDraw };
  var drawableApple = { color: "red", pixels: [apple] };
  var drawableObjects = [drawableSnake, drawableApple];
  CHUNK.draw(drawableObjects);
}

We renamed the drawSnake function and let it take multiple arguments so it can draw an apple.

Next, let's make sure we pass the apple to the draw function, when we call it!

var advanceGame = function() {
  snake = moveSnake(snake);
  if (CHUNK.detectCollisionBetween(snake, CHUNK.gameBoundaries())) {
    CHUNK.endGame();
    CHUNK.flashMessage("Woops! you hit a wall!");
  }
  draw(snake, apple);
}

Finally, let's create an apple to be drawn!

var apple = { top: 8, left: 10 };

Expected Results

What your snake.js file should look like:

var draw = function(snakeToDraw, apple) {
  var drawableSnake = { color: "green", pixels: snakeToDraw };
  var drawableApple = { color: "red", pixels: [apple] };
  var drawableObjects = [drawableSnake, drawableApple];
  CHUNK.draw(drawableObjects);
}

var moveSegment = function(segment) {
  switch(segment.direction) {
    case "down":
      return { top: segment.top + 1, left: segment.left };
    case "up":
      return { top: segment.top - 1, left: segment.left };
    case "right":
      return { top: segment.top, left: segment.left + 1 }
    case "left":
      return { top: segment.top, left: segment.left - 1 }
    default:
      return segment;
  }
}

var segmentFurtherForwardThan = function(index, snake) {
  return snake[index - 1] || snake[index];
}

var moveSnake = function(snake) {
  return snake.map(function(oldSegment, segmentIndex) {
    var newSegment = moveSegment(oldSegment);
    newSegment.direction = segmentFurtherForwardThan(segmentIndex, snake).direction;
    return newSegment;
  });
}

var advanceGame = function() {
  snake = moveSnake(snake);
  if (CHUNK.detectCollisionBetween(snake, CHUNK.gameBoundaries())) {
    CHUNK.endGame();
    CHUNK.flashMessage("Woops! you hit a wall!");
  }
  draw(snake, apple);
}

var changeDirection = function(direction) {
  snake[0].direction = direction;
}

var apple = { top: 8, left: 10 };

var snake = [{ top: 1, left: 0, direction: "down" }, { top: 0, left: 0, direction: "down" }];

CHUNK.executeNTimesPerSecond(advanceGame, 1);
CHUNK.onArrowKey(changeDirection);

How the game should work:

Play Time!

  • Why do you think we put [] around the apple in the draw function?

Next Step: