监听鼠标移动比监听按键更容易：我们只需要监听 mousemove 事件。将以下这行代码添加到与其他事件监听器相同的位置，就在 keyup 事件 的下方。
document.addEventListener("mousemove", mouseMoveHandler);
我们可以根据指针坐标更新挡板的位置 — 以下处理函数将完全实现这一点。将以下函数添加到您的代码中，紧随您刚刚添加的上一行代码之后。
function mouseMoveHandler(e) {
const relativeX = e.clientX - canvas.offsetLeft;
if (relativeX > 0 && relativeX < canvas.width) {
paddleX = relativeX - paddleWidth / 2;
}
}
在此函数中，我们首先计算一个 relativeX 值，它等于视口中的鼠标水平位置 (e.clientX) 减去画布左边缘与视口左边缘之间的距离 (canvas.offsetLeft) — 实际上，这等于画布左边缘与鼠标指针之间的距离。如果相对 X 指针位置大于零且小于画布宽度，则表示指针在画布边界内，然后 paddleX 位置（以挡板左边缘为锚点）被设置为 relativeX 值减去挡板宽度的一半，这样移动将实际相对于挡板的中心。
现在挡板将跟随鼠标光标的位置，但由于我们将移动限制在画布的大小范围内，所以它不会完全消失在两侧。
这是代码的最新状态，供您对照。
<canvas id="myCanvas" width="480" height="320"></canvas>
<button id="runButton">Start game</button>
canvas {
background: #eeeeee;
}
button {
display: block;
}
const canvas = document.getElementById("myCanvas");
const ctx = canvas.getContext("2d");
const ballRadius = 10;
let x = canvas.width / 2;
let y = canvas.height - 30;
let dx = 2;
let dy = -2;
const paddleHeight = 10;
const paddleWidth = 75;
let paddleX = (canvas.width - paddleWidth) / 2;
let rightPressed = false;
let leftPressed = false;
let interval = 0;
const brickRowCount = 5;
const brickColumnCount = 3;
const brickWidth = 75;
const brickHeight = 20;
const brickPadding = 10;
const brickOffsetTop = 30;
const brickOffsetLeft = 30;
let score = 0;
let bricks = [];
for (let c = 0; c < brickColumnCount; c++) {
bricks[c] = [];
for (let r = 0; r < brickRowCount; r++) {
bricks[c][r] = { x: 0, y: 0, status: 1 };
}
}
document.addEventListener("keydown", keyDownHandler);
document.addEventListener("keyup", keyUpHandler);
document.addEventListener("mousemove", mouseMoveHandler);
function keyDownHandler(e) {
if (e.key === "Right" || e.key === "ArrowRight") {
rightPressed = true;
} else if (e.key === "Left" || e.key === "ArrowLeft") {
leftPressed = true;
}
}
function keyUpHandler(e) {
if (e.key === "Right" || e.key === "ArrowRight") {
rightPressed = false;
} else if (e.key === "Left" || e.key === "ArrowLeft") {
leftPressed = false;
}
}
function mouseMoveHandler(e) {
const relativeX = e.clientX - canvas.offsetLeft;
if (relativeX > 0 && relativeX < canvas.width) {
paddleX = relativeX - paddleWidth / 2;
}
}
function collisionDetection() {
for (let c = 0; c < brickColumnCount; c++) {
for (let r = 0; r < brickRowCount; r++) {
let b = bricks[c][r];
if (b.status === 1) {
if (
x > b.x &&
x < b.x + brickWidth &&
y > b.y &&
y < b.y + brickHeight
) {
dy = -dy;
b.status = 0;
score++;
if (score === brickRowCount * brickColumnCount) {
alert("YOU WIN, CONGRATS!");
document.location.reload();
clearInterval(interval); // Needed for Chrome to end game
}
}
}
}
}
}
function drawBall() {
ctx.beginPath();
ctx.arc(x, y, ballRadius, 0, Math.PI * 2);
ctx.fillStyle = "#0095DD";
ctx.fill();
ctx.closePath();
}
function drawPaddle() {
ctx.beginPath();
ctx.rect(paddleX, canvas.height - paddleHeight, paddleWidth, paddleHeight);
ctx.fillStyle = "#0095DD";
ctx.fill();
ctx.closePath();
}
function drawBricks() {
for (let c = 0; c < brickColumnCount; c++) {
for (let r = 0; r < brickRowCount; r++) {
if (bricks[c][r].status === 1) {
const brickX = r * (brickWidth + brickPadding) + brickOffsetLeft;
const brickY = c * (brickHeight + brickPadding) + brickOffsetTop;
bricks[c][r].x = brickX;
bricks[c][r].y = brickY;
ctx.beginPath();
ctx.rect(brickX, brickY, brickWidth, brickHeight);
ctx.fillStyle = "#0095DD";
ctx.fill();
ctx.closePath();
}
}
}
}
function drawScore() {
ctx.font = "16px Arial";
ctx.fillStyle = "#0095DD";
ctx.fillText(`Score: ${score}`, 8, 20);
}
function draw() {
ctx.clearRect(0, 0, canvas.width, canvas.height);
drawBricks();
drawBall();
drawPaddle();
drawScore();
collisionDetection();
if (x + dx > canvas.width - ballRadius || x + dx < ballRadius) {
dx = -dx;
}
if (y + dy < ballRadius) {
dy = -dy;
} else if (y + dy > canvas.height - ballRadius) {
if (x > paddleX && x < paddleX + paddleWidth) {
dy = -dy;
} else {
alert("GAME OVER");
document.location.reload();
clearInterval(interval); // Needed for Chrome to end game
}
}
if (rightPressed && paddleX < canvas.width - paddleWidth) {
paddleX += 7;
} else if (leftPressed && paddleX > 0) {
paddleX -= 7;
}
x += dx;
y += dy;
}
function startGame() {
interval = setInterval(draw, 10);
}
const runButton = document.getElementById("runButton");
runButton.addEventListener("click", () => {
startGame();
runButton.disabled = true;
});
注意： 尝试调整挡板移动的边界，以便整个挡板在画布的两侧都可见，而不仅仅是一半。
现在我们有了一个完整的游戏，我们将用一些小的调整来结束我们的课程系列 — 收尾工作。