Pointer Lock API（3/3）：一个Demo
简单的Demo演练
点击跳转至Code Pen以查看演示和源码
完整代码
<!DOCTYPE HTML>
<html lang="en-US">
<head>
<meta charset="UTF-8">
<title>Pointer lock demo</title>
<link type="text/css" rel="stylesheet" href="style.css">
<style>
html,
body {
margin: 0;
padding: 0;
}
html {
font-family: sans-serif;
}
canvas {
display: block;
margin: 0 auto;
border: 1px solid black;
}
.information {
width: 640px;
margin: 0 auto 50px;
}
#tracker {
position: absolute;
top: 0;
right: 10px;
background-color: white;
}
h1 {
font-size: 200%;
}
</style>
</head>
<body>
<div class="information">
<h1>Pointer lock demo</h1>
<p>本演示演示了指针锁API的用法。 单击画布区域，您的鼠标将直接控制画布内的球，而不是鼠标指针。 您可以按Escape键以返回到标准预期状态。</p>
</div>
<canvas width="640" height="360">
Your browser does not support HTML5 canvas
</canvas>
<div id="tracker"></div>
<script src="app.js"></script>
</body>
<script>
const RADIUS = 20;
function degToRad(degrees) {
var result = Math.PI / 180 * degrees;
return result;
}
// setup of the canvas
var canvas = document.querySelector('canvas');
var ctx = canvas.getContext('2d');
var x = 50;
var y = 50;
function canvasDraw() {
ctx.fillStyle = "black";
ctx.fillRect(0, 0, canvas.width, canvas.height);
ctx.fillStyle = "#f00";
ctx.beginPath();
ctx.arc(x, y, RADIUS, 0, degToRad(360), true);
ctx.fill();
}
canvasDraw();
// pointer lock object forking for cross browser
canvas.requestPointerLock = canvas.requestPointerLock ||
canvas.mozRequestPointerLock;
document.exitPointerLock = document.exitPointerLock ||
document.mozExitPointerLock;
canvas.onclick = function() {
canvas.requestPointerLock();
};
// pointer lock event listeners
// Hook pointer lock state change events for different browsers
document.addEventListener('pointerlockchange', lockChangeAlert, false);
document.addEventListener('mozpointerlockchange', lockChangeAlert, false);
function lockChangeAlert() {
if (document.pointerLockElement === canvas ||
document.mozPointerLockElement === canvas) {
console.log('The pointer lock status is now locked');
document.addEventListener("mousemove", updatePosition, false);
} else {
console.log('The pointer lock status is now unlocked');
document.removeEventListener("mousemove", updatePosition, false);
}
}
var tracker = document.getElementById('tracker');
var animation;
function updatePosition(e) {
x += e.movementX;
y += e.movementY;
if (x > canvas.width + RADIUS) {
x = -RADIUS;
}
if (y > canvas.height + RADIUS) {
y = -RADIUS;
}
if (x < -RADIUS) {
x = canvas.width + RADIUS;
}
if (y < -RADIUS) {
y = canvas.height + RADIUS;
}
tracker.textContent = "X position: " + x + ", Y position: " + y;
if (!animation) {
animation = requestAnimationFrame(function() {
animation = null;
canvasDraw();
});
}
}
</script>
</html>
代码说明
设定x,y 初始值：
var x = 50;
var y = 50;
指针锁定方法（这里考虑了firefox浏览器兼容）：
//声明
canvas.requestPointerLock = canvas.requestPointerLock || canvas.mozRequestPointerLock;
//退出
document.exitPointerLock = document.exitPointerLock || document.mozExitPointerLock;
现在，我们给canvas设定一个点击事件来监听触发requestPointerLock()方法，当点击时，将启动指针锁定。：
canvas.onclick = function() { //canvas元素绑定点击事件
canvas.requestPointerLock();
}
对于专用指针锁定事件侦听器：pointerlockchange。我们运行一个名为lockChangeAlert()的函数来处理更改。
// pointer lock event listener
// Hook pointer lock state change events for different browsers
document.addEventListener('pointerlockchange', lockChangeAlert, false);
document.addEventListener('mozpointerlockchange', lockChangeAlert, false);
该函数检查poinLockElement 属性，是不是我们的canvas元素，如果是，则通过附加一个事件侦听函数updatePosition()来处理鼠标移动。如果不是，他将再次移除事件侦听。
function lockChangeAlert() {
if (document.pointerLockElement === canvas ||
document.mozPointerLockElement === canvas) {
console.log('The pointer lock status is now locked');
document.addEventListener("mousemove", updatePosition, false);
} else {
console.log('The pointer lock status is now unlocked');
document.removeEventListener("mousemove", updatePosition, false);
}
}
该updatePosition()函数更新canvas中小球的位置（x，y值），同时也包括了if条件判断检查小球是否超出了canvas画布的边界。如果是，那么它会让小球绕到对面的那边，它还包括检查之前是否已经进行了requestAnimationFrame()调用，如果进行了调用，就会再次以required被调用，并且唤起canvasDraw()函数，来更行canvas画面，还设置了一个跟踪器，以将X和Y值写到屏幕上，以供参考。
var tracker = document.getElementById('tracker');
var animation;
function updatePosition(e) {
x += e.movementX;
y += e.movementY;
if (x > canvas.width + RADIUS) {
x = -RADIUS;
}
if (y > canvas.height + RADIUS) {
y = -RADIUS;
}
if (x < -RADIUS) {
x = canvas.width + RADIUS;
}
if (y < -RADIUS) {
y = canvas.height + RADIUS;
}
tracker.textContent = "X position: " + x + ", Y position: " + y;
if (!animation) {
animation = requestAnimationFrame(function() {
animation = null;
canvasDraw();
});
}
}
canvasDraw()函数以最新的坐标绘制小球的位置
function canvasDraw() {
ctx.fillStyle = "black";
ctx.fillRect(0, 0, canvas.width, canvas.height);
ctx.fillStyle = "#f00";
ctx.beginPath();
ctx.arc(x, y, RADIUS, 0, degToRad(360), true);
ctx.fill();
}
