<!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();
}
var myGameArea = { canvas : document.createElement("canvas"), start : function() { this.canvas.width = 480;
this.canvas.height = 270;
this.context = this.canvas.getContext("2d"); document.body.insertBefore(this.canvas, document.body.childNodes[0]);
this.frameNo = 0;
this.interval = setInterval(updateGameArea, 20);
},
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 = 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>红色方块将向前移动。</p>
<p>请尝试改变 speed 属性，你会看到红色方块会以相应的速度移动。</p>
</body>
</html>