javascript - 当我添加命中检测时，我的 Canvas 消失了

Question

我目前正在开发一个小型 js 游戏，只是为了好玩。

但是每当我向立方体添加命中检测时，我的整个 Canvas 就会消失。我不知道是什么原因造成的，因此我在这里问。我将添加两个片段。一张在我添加命中检测之前，一张在我添加命中检测之后。我希望有人能帮助我。

var myGamePiece;

function startGame() {
    myGamePiece = new component(30, 30, "red", 225, 225);
    myGameArea.start();
}

var myGameArea = {
    canvas : document.createElement("canvas"),
    start : function() {
        this.canvas.width = 500;
        this.canvas.height = 500;
        this.context = this.canvas.getContext("2d");
        document.body.insertBefore(this.canvas, document.body.childNodes[0]);
        this.frameNo = 0;
        this.interval = setInterval(updateGameArea, 20);
        window.addEventListener('keydown', function (e) {
            e.preventDefault();
            myGameArea.keys = (myGameArea.keys || []);
            myGameArea.keys[e.keyCode] = (e.type == "keydown");
        })
        window.addEventListener('keyup', function (e) {
            myGameArea.keys[e.keyCode] = (e.type == "keydown");
        })
    },
    stop : function() {
        clearInterval(this.interval);
    },    
    clear : function() {
        this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
    }
}

function component(width, height, color, x, y, type) {

    this.type = type;
    this.width = width;
    this.height = height;
    this.speed = 0;
    this.angle = 0;
    this.moveAngle = 0;
    this.x = x;
    this.y = y;    
    this.update = function() {
        ctx = myGameArea.context;
        ctx.save();
        ctx.translate(this.x, this.y);
        ctx.rotate(this.angle);
        ctx.fillStyle = color;
        ctx.fillRect(this.width / -2, this.height / -2, this.width, this.height);
        ctx.restore();    
    }
    this.newPos = function() {
        this.angle += this.moveAngle * Math.PI / 180;
        this.x += this.speed * Math.sin(this.angle);
        this.y -= this.speed * Math.cos(this.angle);
    }
}

function updateGameArea() {
    myGameArea.clear();
    myGamePiece.moveAngle = 0;
    myGamePiece.speed = 0;
    if (myGameArea.keys && myGameArea.keys[37]) {myGamePiece.moveAngle = -2; }
    if (myGameArea.keys && myGameArea.keys[39]) {myGamePiece.moveAngle = 2; }
    if (myGameArea.keys && myGameArea.keys[38]) {myGamePiece.speed= 2; }
    if (myGameArea.keys && myGameArea.keys[40]) {myGamePiece.speed= -2; }
    myGamePiece.newPos();
    myGamePiece.update();
}

这是我添加障碍物和命中检测的地方

如果您将其放入 Canvas (HTML 格式)中，整个 Canvas 将会消失，或者至少这就是发生在我身上的情况。

var myGamePiece;
var myObstacle;

function startGame() {
    myGamePiece = new component(30, 30, "red", 225, 225);
    myObstacle = new component(40, 40, "green", 300, 120); 
    myGameArea.start();
}

var myGameArea = {
    canvas : document.createElement("canvas"),
    start : function() {
        this.canvas.width = 500;
        this.canvas.height = 500;
        this.context = this.canvas.getContext("2d");
        document.body.insertBefore(this.canvas, document.body.childNodes[0]);
        this.frameNo = 0;
        this.interval = setInterval(updateGameArea, 20);
        window.addEventListener('keydown', function (e) {
            e.preventDefault();
            myGameArea.keys = (myGameArea.keys || []);
            myGameArea.keys[e.keyCode] = (e.type == "keydown");
        })
        window.addEventListener('keyup', function (e) {
            myGameArea.keys[e.keyCode] = (e.type == "keydown");
        })
    },
    stop : function() {
        clearInterval(this.interval);
    },    
    clear : function() {
        this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
    }
}

function component(width, height, color, x, y, type) {

    this.type = type;
    this.width = width;
    this.height = height;
    this.speed = 0;
    this.angle = 0;
    this.moveAngle = 0;
    this.x = x;
    this.y = y;    
    this.update = function() {
        ctx = myGameArea.context;
        ctx.save();
        ctx.translate(this.x, this.y);
        ctx.rotate(this.angle);
        ctx.fillStyle = color;
        ctx.fillRect(this.width / -2, this.height / -2, this.width, this.height);
        ctx.restore();    
    }
    this.newPos = function() {
        this.angle += this.moveAngle * Math.PI / 180;
        this.x += this.speed * Math.sin(this.angle);
        this.y -= this.speed * Math.cos(this.angle);
    }
     }
  this.crashWith = function(otherobj) {
    var myleft = this.x;
    var myright = this.x + (this.width);
    var mytop = this.y;
    var mybottom = this.y + (this.height);
    var otherleft = otherobj.x;
    var otherright = otherobj.x + (otherobj.width);
    var othertop = otherobj.y;
    var otherbottom = otherobj.y + (otherobj.height);
    var crash = true;
    if ((mybottom < othertop) ||
    (mytop > otherbottom) ||
    (myright < otherleft) ||
    (myleft > otherright)) {
      crash = false;
    }
    return crash;
  }


function updateGameArea() {
    if (myGamePiece.crashWith(myObstacle)) {
    myGameArea.stop();
  } else {
    myGameArea.clear();
    myObstacle.update();
    myGamePiece.moveAngle = 0;
    myGamePiece.speed = 0;
    if (myGameArea.keys && myGameArea.keys[37]) {myGamePiece.moveAngle = -2; }
    if (myGameArea.keys && myGameArea.keys[39]) {myGamePiece.moveAngle = 2; }
    if (myGameArea.keys && myGameArea.keys[38]) {myGamePiece.speed= 2; }
    if (myGameArea.keys && myGameArea.keys[40]) {myGamePiece.speed= -2; }
    myGamePiece.newPos();
    myGamePiece.update();
}

Answer 1

当我复制您的第二个代码片段时，我注意到代码在某些地方缺少括号。因此我也没有 Canvas 。

所以，后面多了一个:

this.newPos = function() {
    this.angle += this.moveAngle * Math.PI / 180;
    this.x += this.speed * Math.sin(this.angle);
    this.y -= this.speed * Math.cos(this.angle);
}
 } <-- //This guy

您在组件函数末尾缺少一个:

    }
    return crash;
  }
"}" <-- //This one is missing

最后，您错过了 updateGameArea() 函数的结束函数:

    myGamePiece.update();
    }
"}" <-- //This one is missing too

之后，我只是在开始时将 myGameArea 对象与其他对象一起移动(不是强制性的，但最好将所有变量放在一起)，称为:

startGame()

瞧!

这些类型的错误不会真正显示在控制台中，但您可以通过在代码上运行一些自动格式/自动缩进来注意到它们。 如果代码没有很好地缩进，那么您很可能错过了括号。