鼠标控制

这是 Gamedev Canvas 教程的 10 步中的第 **9 步**。您可以在 Gamedev-Canvas-workshop/lesson9.html 中找到完成本课后代码应该具有的样子。

游戏本身实际上已经完成了，所以让我们着手完善它。我们已经添加了键盘控制，但我们也可以轻松地添加鼠标控制。

监听鼠标移动

监听鼠标移动比监听按键事件还要容易：我们只需要监听 mousemove 事件。将以下行添加到其他事件监听器中的相同位置，就在 keyup 事件 下面

document.addEventListener("mousemove", mouseMoveHandler, false);

将球拍的移动绑定到鼠标的移动

我们可以根据指针坐标更新球拍的位置——以下处理程序函数将执行此操作。将以下函数添加到您的代码中，位于您添加的上一行下面

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 relativeX 值，该值等于视窗中的水平鼠标位置 (e.clientX) 减去画布左边缘和视窗左边缘之间的距离 (canvas.offsetLeft)——实际上，这等于画布左边缘和鼠标指针之间的距离。如果相对 X 指针位置大于 0 且小于画布宽度，则指针在画布边界内，并且 paddleX 位置（锚定在球拍的左边缘）设置为 relativeX 值减去球拍宽度的一半，这样移动实际上将相对于球拍的中间进行。

现在，球拍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内，因此它不会完全消失在任何一侧。

比较你的代码

这是与之进行比较的最新代码状态

<canvas id="myCanvas" width="480" height="320"></canvas>
<button id="runButton">Start game</button>

canvas {
  background: #eee;
}
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, false);
document.addEventListener("keyup", keyUpHandler, false);
document.addEventListener("mousemove", mouseMoveHandler, false);

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);
}

document.getElementById("runButton").addEventListener("click", function () {
  startGame();
});

注意：尝试调整球拍移动的边界，以便整个球拍在画布的两侧都可见，而不仅仅是它的一半。

下一步

现在我们已经完成了一个完整的游戏，我们将通过一些小的调整来结束我们的课程系列——收尾工作。