javascript - 贪吃蛇游戏无法运行 - JavaScript for Kids

Question

已关闭。这个问题是 not reproducible or was caused by typos 。目前不接受答案。

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这个问题是由拼写错误或无法再重现的问题引起的。虽然类似的问题可能是 on-topic在这里，这个问题的解决方式不太可能帮助 future 的读者。

已关闭 5 年前。

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我花了一整夜的时间绞尽脑汁试图找出为什么我的代码不起作用。我把代码复制了2次，但结果都是一样的。问题是，有时当蛇吃掉苹果时，它就不起作用了。蛇会从苹果旁边走过，就像它不在那里一样。请帮我解决这个问题，我想完成它。 (我添加了 jQuery)

`
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

var width = canvas.width;
var height = canvas.height;

var blockSize = 10;
var widthInBlocks = width / blockSize;
var heightInBlocks = height / blockSize;

var score = 0;

var drawBorder = function () {
ctx.fillStyle = "Gray";
ctx.fillRect(0, 0, width, blockSize);
ctx.fillRect(0, height - blockSize, width, blockSize);
ctx.fillRect(0, 0, blockSize, height);
ctx.fillRect(width - blockSize, 0, blockSize, height);
};

var drawScore = function () {
ctx.font = "20px Courier";
ctx.fillStyle = "Black";
ctx.textAlign = "left";
ctx.textBaseline = "top";
ctx.fillText("Score: " + score, blockSize, blockSize);
};

var gameOver = function () {
clearInterval(intervalId);
ctx.font = "60px Courier";
ctx.fillStyle = "Black";
ctx.textAlign = "center";
ctx.textBaseline = "middle";
ctx.fillText("Game Over", width / 2, height / 2);
};

var circle = function (x, y, radius, fillCircle) {
ctx.beginPath();
ctx.arc(x, y, radius, 0, Math.PI * 2, false);
if (fillCircle) {
    ctx.fill();
} else {
    ctx.stroke();
}
};

var Block = function (col, row) {
this.col = col;
this.row = row;
};

Block.prototype.drawSquare = function (color) {
var x = this.col * blockSize;
var y = this.row * blockSize;
ctx.fillStyle = color;
ctx.fillRect(x, y, blockSize, blockSize);
};

Block.prototype.drawCircle = function (color) {
var centerX = this.col * blockSize + blockSize / 2;
var centerY = this.row * blockSize + blockSize / 2;
ctx.fillStyle = color;
circle(centerX, centerY, blockSize / 2, true);
};

Block.prototype.equal = function (otherBlock) {
return this.col === otherBlock.col && this.row === otherBlock.row;
};


var Snake = function () {
this.segments = [
new Block(7, 5),
new Block(6, 5),
new Block(5, 5)
];
this.direction = "right";
this.nextDirection = "right";
};

Snake.prototype.draw = function () {
for (var i = 0; i < this.segments.length; i++) {
    this.segments[i].drawSquare("Blue");
}
};


Snake.prototype.move = function () {
var head = this.segments[0];
var newHead;

this.direction = this.nextDirection;

if (this.direction === "right") {
newHead = new Block(head.col + 1, head.row);
} else if (this.direction === "down") {
newHead = new Block(head.col, head.row + 1);
} else if (this.direction === "left") {
newHead = new Block(head.col - 1, head.row);
} else if (this.direction === "up") {
newHead = new Block(head.col, head.row - 1);
}

if (this.checkCollision(newHead)) {
gameOver();
return;
}

this.segments.unshift(newHead);

if (newHead.equal(apple.position)) {
score++;
apple.move();
} else {
this.segments.pop();
};
};

Snake.prototype.checkCollision = function (head) {
var leftCollision = (head.col === 0);
var topCollision = (head.row === 0);
var rightCollision = (head.col === widthInBlocks - 1);
var bottomCollision = (head.row === widthInBlocks - 1);

var wallCollision = leftCollision || topCollision || rightCollision ||           bottomCollision;

var selfCollision = false;

for (var i = 0; i < this.segments.length; i++) {
    if (head.equal(this.segments[i])) {
        selfCollision = true;
    }
}

return wallCollision || selfCollision;
};

Snake.prototype.setDirection = function (newDirection) {
if (this.direction === "up" && newDirection === "down") {
    return;
} else if (this.direction === "right" && newDirection === "left") {
    return;
} else if (this.direction === "down" && newDirection === "up") {
    return;
} else if (this.direction === "left" && newDirection === "right") {
    return;
}

this.nextDirection = newDirection;
};

var Apple = function () {
this.position = new Block(10, 10);
};

Apple.prototype.draw = function () {
this.position.drawCircle("LimeGreen");
};


Apple.prototype.move = function () {
var randomCol = Math.floor(Math.random() * (widthInBlocks - 2)) + 1;
var randomRow = Math.floor(Math.random() * (heightInBlocks - 2)) + 1;
this.position = new Block(randomCol, randomRow);
};

var snake = new Snake();
var apple = new Apple();

var intervalId = setInterval(function () {
ctx.clearRect(0, 0, width, height);
drawScore();
snake.move();
snake.draw();
apple.draw();
drawBorder();
}, 100);

var directions = {
37: "left",
38: "up",
39: "right",
40: "down"
};

$("body").keydown(function (event) {
var newDirection = directions[event.keyCode];
if (newDirection !== undefined) {
    snake.setDirection(newDirection);
}
});
`

Answer 1

<script src="https://code.jquery.com/jquery-2.1.0.js"></script>

<script>
//// Set up canvas
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

// // Get the width and height from the canvas element
var width = canvas.width;
var height = canvas.height;

//// Work out the width and height in blocks
var blockSize = 10;
var widthInBlocks = width / blockSize;
var heightInBlocks = height / blockSize;

// // Set score to 0
var score = 0;

// // Draw the border
var drawBorder = function () {
  ctx.fillStyle = "Gray";
  ctx.fillRect(0, 0, width, blockSize);
  ctx.fillRect(0, height - blockSize, width, blockSize);
  ctx.fillRect(0, 0, blockSize, height);
  ctx.fillRect(width - blockSize, 0, blockSize, height);
};

// // Draw the score in the top-left corner
var drawScore = function () {
  ctx.font = "20px Courier";
  ctx.fillStyle = "Black";
  ctx.textAlign = "left";
  ctx.textBaseline = "top";
  ctx.fillText("Score: " + score, blockSize, blockSize);
};

// // Clear the interval and display Game Over text
var gameOver = function () {
  clearInterval(intervalId);
  ctx.font = "60px Courier";
  ctx.fillStyle = "Black";
  ctx.textAlign = "center";
  ctx.textBaseline = "middle";
  ctx.fillText("Game Over", width / 2, height / 2);
};

// // Draw a circle (using the function from Chapter 14)
var circle = function (x, y, radius, fillCircle) {
  ctx.beginPath();
  ctx.arc(x, y, radius, 0, Math.PI * 2, false);
  if (fillCircle) {
    ctx.fill();
  } else {
    ctx.stroke();
  }
};

// // The Block constructor
var Block = function (col, row) {
  this.col = col;
  this.row = row;
};

// // Draw a square at the block's location
Block.prototype.drawSquare = function (color) {
  var x = this.col * blockSize;
  var y = this.row * blockSize;
  ctx.fillStyle = color;
  ctx.fillRect(x, y, blockSize, blockSize);
};

// // Draw a circle at the block's location
Block.prototype.drawCircle = function (color) {
  var centerX = this.col * blockSize + blockSize / 2;
  var centerY = this.row * blockSize + blockSize / 2;
  ctx.fillStyle = color;
  circle(centerX, centerY, blockSize / 2, true);
};

// // Check if this block is in the same location as another block
Block.prototype.equal = function (otherBlock) {
  return this.col === otherBlock.col && this.row === otherBlock.row;
};

// // The Snake constructor
var Snake = function () {
  this.segments = [
    new Block(7, 5),
    new Block(6, 5),
    new Block(5, 5)
  ];

  this.direction = "right";
  this.nextDirection = "right";
};

// // Draw a square for each segment of the snake's body
Snake.prototype.draw = function () {
  this.segments[0].drawSquare("LimeGreen");
  var isEvenSegment = false;

  for (var i = 1; i < this.segments.length; i++) {
    if (isEvenSegment) {
      this.segments[i].drawSquare("Blue");
    } else {
      this.segments[i].drawSquare("Yellow");
    }

    isEvenSegment = !isEvenSegment; // следующий сегмент будет нечетным
  }
};

// // Create a new head and add it to the beginning of
// the snake to move the snake in its current direction
Snake.prototype.move = function () {
  var head = this.segments[0];
  var newHead;

  this.direction = this.nextDirection;

  if (this.direction === "right") {
    newHead = new Block(head.col + 1, head.row);
  } else if (this.direction === "down") {
    newHead = new Block(head.col, head.row + 1);
  } else if (this.direction === "left") {
    newHead = new Block(head.col - 1, head.row);
  } else if (this.direction === "up") {
    newHead = new Block(head.col, head.row - 1);
  }

  if (this.checkCollision(newHead)) {
    gameOver();
    return;
  }

  this.segments.unshift(newHead);

  if (newHead.equal(apple.position)) {
    score++;
    apple.move();
  } else {
    this.segments.pop();
  }
};

// // Check if the snake's new head has collided with the wall or itself
Snake.prototype.checkCollision = function (head) {
  var leftCollision = (head.col === 0);
  var topCollision = (head.row === 0);
  var rightCollision = (head.col === widthInBlocks - 1);
  var bottomCollision = (head.row === heightInBlocks - 1);

  var wallCollision = leftCollision || topCollision || rightCollision || bottomCollision;

  var selfCollision = false;

  for (var i = 0; i < this.segments.length; i++) {
    if (head.equal(this.segments[i])) {
      selfCollision = true;
    }
  }

  return wallCollision || selfCollision;
};

// // Set the snake's next direction based on the keyboard
Snake.prototype.setDirection = function (newDirection) {
  if (this.direction === "up" && newDirection === "down") {
    return;
  } else if (this.direction === "right" && newDirection === "left") {
    return;
  } else if (this.direction === "down" && newDirection === "up") {
    return;
  } else if (this.direction === "left" && newDirection === "right") {
    return;
  }

  this.nextDirection = newDirection;
};

// // The Apple constructor
var Apple = function () {
  this.position = new Block(10, 10);
};

//  // Draw a circle at the apple's location
Apple.prototype.draw = function () {
  this.position.drawCircle("LimeGreen");
};

// // Move the apple to a new random location
Apple.prototype.move = function () {
  var randomCol = Math.floor(Math.random() * (widthInBlocks - 2)) + 1;
  var randomRow = Math.floor(Math.random() * (heightInBlocks - 2)) + 1;
  this.position = new Block(randomCol, randomRow);
};

// // Create the snake and apple objects
var snake = new Snake();
var apple = new Apple();

//// Pass an animation function to setInterval
var intervalId = setInterval(function () {
  ctx.clearRect(0, 0, width, height);
  drawScore();
  snake.move();
  snake.draw();
  apple.draw();
  drawBorder();
}, 100);

// // Convert keycodes to directions
var directions = {
  37: "left",
  38: "up",
  39: "right",
  40: "down"
};

// // The keydown handler for handling direction key presses
$("body").keydown(function (event) {
  var newDirection = directions[event.keyCode];
  if (newDirection !== undefined) {
    snake.setDirection(newDirection);
  }
});
</script>