如何在 canvas 中旋转物体时使用键盘 360* 射击子弹？

Question

我希望我的物体在旋转或移动时朝我的物体所面对的方向射击，关于如何做到这一点有什么想法吗？

我也是初学者，我几天前才开始学习，所以我很难找到代码并学习它们，而且我找不到好的老师或网站。这是代码，我尝试了一些但我很确定它完全失败了..

var myGamePiece;

function startGame() {
    bullet = new component(5, 5, 'blue', 300, 300);
    myGamePiece = new component(30, 30, "red", 225, 225);
    myGameArea.start();
}

var myGameArea = {
    canvas : document.createElement("canvas"),
    start : function() {
        this.canvas.width = 1400;
        this.canvas.height = 750;
        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.speedx = 0;
    this.speedy = 0;
    this.angle = 0;
    this.moveAngle = 0;
    this.x = x;
    this.y = y;  
    this.s = x;
    this.u = 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.speedx;
        this.y += this.speedy;
        this.s += this.speed * Math.sin(this.angle);
        this.u -= this.speed * Math.cos(this.angle);
    }
}

function updateGameArea() {
    myGameArea.clear();
    myGamePiece.moveAngle = 0;
    myGamePiece.speedx = 0;
    myGamePiece.speedy = 0;
    bullet.speed = 0;
    if (myGameArea.keys && myGameArea.keys[90]) {myGamePiece.moveAngle = -3; }
    if (myGameArea.keys && myGameArea.keys[88]) {myGamePiece.moveAngle = 3; }
    if (myGameArea.keys && myGameArea.keys[38]) {myGamePiece.speedy= -2; }
    if (myGameArea.keys && myGameArea.keys[40]) {myGamePiece.speedy= 2; }
    if (myGameArea.keys && myGameArea.keys[39]) {myGamePiece.speedx= 2; }
    if (myGameArea.keys && myGameArea.keys[37]) {myGamePiece.speedx= -2; }
    if (myGameArea.keys && myGameArea.keys[32]) {bullet.speed= -3; }
    bullet.newPos();  
    bullet.update();
    myGamePiece.newPos();
    myGamePiece.update();
}

Answer 1

window.onload = function() {
var myGamePiece;
var bullet;
var myGameArea;
var ctx;

function startGame() {
    bullet = new component(5, 5, 'blue', 300, 300);
    myGamePiece = new component(30, 30, "red", 225, 225);
    myGameArea.start();
}

var myGameArea = {
    canvas : document.createElement("canvas"),
    start : function() {
        this.canvas.width = 1400;
        this.canvas.height = 750;
        this.context = this.canvas.getContext("2d");
        document.body.insertBefore(this.canvas, document.body.childNodes[0]);
        this.frameNo = 0;
        bullet.speed = 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.angle = 0;
    this.moveAngle = 0;
    this.x = x;
    this.y = y;  
    this.speed = 0;
    this.speedx = 0;
    this.speedy = 0;

    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.speedx;
        this.y += this.speedy;
        this.x += this.speed * Math.cos(this.angle);
        this.y += this.speed * Math.sin(this.angle);
    }
}

function updateGameArea() {
    myGameArea.clear();
    myGamePiece.moveAngle = 0;
    myGamePiece.speedx = 0;
    myGamePiece.speedy = 0;
    
    if (myGameArea.keys && myGameArea.keys[90]) {myGamePiece.moveAngle = -3; }
    if (myGameArea.keys && myGameArea.keys[88]) {myGamePiece.moveAngle = 3; }
    if (myGameArea.keys && myGameArea.keys[38]) {myGamePiece.speedy= -2; }
    if (myGameArea.keys && myGameArea.keys[40]) {myGamePiece.speedy= 2; }
    if (myGameArea.keys && myGameArea.keys[39]) {myGamePiece.speedx= 2; }
    if (myGameArea.keys && myGameArea.keys[37]) {myGamePiece.speedx= -2; }
    if (myGameArea.keys && myGameArea.keys[32]) {
        bullet.angle = myGamePiece.angle;
        bullet.x = myGamePiece.x;
        bullet.y = myGamePiece.y;
        bullet.speed= 3; 
    }
    bullet.newPos();  
    bullet.update();
    myGamePiece.newPos();
    myGamePiece.update();
}


startGame();

}

你几乎已经成功了，最大的问题是 bullet.speed = 0；在游戏循环中让它永远不会移动。

您还更新了 this.s 和 this.u，但它从未在其他地方使用过，所以我修复了这部分。

this.s += this.speed * Math.sin(this.angle);
this.u -= this.speed * Math.cos(this.angle);

我还添加了一些额外的代码，以便它从红色立方体位置触发。

最好将您的代码与我的更改进行比较，看看还有哪些更改，但我认为我已经突出了要点。

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