W3Schools Tryit 编辑器 - W3Schools 中文教程

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
<style>
canvas {
    border:1px solid #d3d3d3;
    background-color: #f1f1f1;
}
</style>
</head>
<body onload="startGame()">
<script>

var myGamePiece;

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

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

this.type = type;
    this.width = width;
    this.height = height;
    this.speed = 1;
    this.angle = 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.x += this.speed * Math.sin(this.angle);
        this.y -= this.speed * Math.cos(this.angle);
    }
}

function updateGameArea() {
    myGameArea.clear();
    myGamePiece.newPos();
    myGamePiece.update();
}

</script>

<p>The red square will move forward.</p>
<p>Try changing the speed property, and you will see the red square will move accordingly.</p>
</body>
</html>