用HTML5的＜canvas＞元素实现刮刮乐游戏

用HTML5的<canvas>元素实现刮刮乐，要求：将上面的“图层”的图像可用鼠标刮去，露出下面的“图层”的图像。

示例从简单到复杂。

简单示例

准备两张图像，我这里上面的图像top_image.png，下面的图像bottom_image.png，如下图：

我这里为方便，经图片和源码文件放在同一个文件夹中。

先看用一个canvas元素实现刮刮乐，源码如下：

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>刮刮乐（Scratch Card）</title><style>* {margin: 0;padding: 0;box-sizing: border-box;}body {height: 100vh;display: flex;justify-content: center;align-items: center;background-color: #f0f0f0; /* 背景色 */}canvas {background-image: url('bottom_image.png'); /* 底层图片 */background-size: cover;}</style>
</head>
<body><canvas id="canvas" width="356" height="358"></canvas><script>var canvas = document.getElementById("canvas");var ctx = canvas.getContext("2d");// 加载上层图片（可被刮去的图层）var img = new Image();img.src = "top_image.png"; // 上层图片路径img.onload = function() {ctx.drawImage(img, 0, 0, canvas.width, canvas.height);};// 标记是否按下鼠标（开始刮卡）var isDown = false;// 鼠标按下事件canvas.addEventListener('mousedown', function() {isDown = true;// 切换到“擦除”模式ctx.globalCompositeOperation = 'destination-out';});// 鼠标松开事件canvas.addEventListener('mouseup', function() {isDown = false;});// 鼠标移动事件canvas.addEventListener('mousemove', function(event) {if (isDown) {let x = event.offsetX;let y = event.offsetY;// 绘制擦除效果ctx.beginPath();ctx.arc(x, y, 20, 0, Math.PI * 2, false); // 使用圆形笔触ctx.fill();ctx.closePath();}});</script>
</body>
</html>

下面用两个canvas元素实现刮刮乐，底层图片和上层图片各用一个canvas元素，效果和上面的一样。实现的源码如下：

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>刮刮乐（Scratch Card）2</title><style>* {margin: 0;padding: 0;box-sizing: border-box;}body {height: 100vh;display: flex;justify-content: center;align-items: center;background-color: #f0f0f0;}#container {position: relative;width: 356px;height: 358px;}canvas {position: absolute;top: 0;left: 0;}</style>
</head>
<body><div id="container"><canvas id="bottomCanvas" width="356" height="358"></canvas> <!-- 底层Canvas --><canvas id="topCanvas" width="356" height="358"></canvas> <!-- 上层Canvas --></div><script>document.addEventListener('DOMContentLoaded', function() {var bottomCanvas = document.getElementById('bottomCanvas');var topCanvas = document.getElementById('topCanvas');var bottomCtx = bottomCanvas.getContext('2d');var topCtx = topCanvas.getContext('2d');// 加载底层图片var bottomImage = new Image();bottomImage.src = 'bottom_image.png'; // 底层图片路径bottomImage.onload = function() {bottomCtx.drawImage(bottomImage, 0, 0, bottomCanvas.width, bottomCanvas.height);};// 加载上层图片var topImage = new Image();topImage.src = 'top_image.png'; // 上层图片路径topImage.onload = function() {topCtx.drawImage(topImage, 0, 0, topCanvas.width, topCanvas.height);};var isDown = false;// 鼠标按下事件topCanvas.addEventListener('mousedown', function() {isDown = true;topCtx.globalCompositeOperation = 'destination-out';});// 鼠标松开事件topCanvas.addEventListener('mouseup', function() {isDown = false;});// 鼠标移动事件topCanvas.addEventListener('mousemove', function(event) {if (!isDown) return;var x = event.offsetX;var y = event.offsetY;// 绘制擦除效果topCtx.beginPath();topCtx.arc(x, y, 20, 0, Math.PI * 2, false); // 使用圆形笔触topCtx.fill();topCtx.closePath();});});</script>
</body>
</html>

复杂示例

下面是改进，从列表框（下拉框）选择图片刮刮乐，增加了游戏的趣味性。

先给出效果

项目（project）的目录结构如下：

我这里游戏图片：

源码如下：

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>刮刮乐（Scratch Card）3</title><style>div{ margin:20px;text-align:center;}* {margin: 0;padding: 0;box-sizing: border-box;}body {height: 100vh;display: flex;justify-content: center;align-items: center;background-color: #f0f0f0;}#container {position: relative;width: 356px;height: 358px;}canvas {position: absolute;top: 0;left: 0;}</style>
</head>
<body><div> 选择游戏图片<select id="mySelect" onchange="loadImages()"> <!-- 添加 onchange 事件 --><option value="1">1</option> <!-- 更改 value 以匹配图像名称 --><option value="2">2</option><option value="3">3</option></select><div><div id="container"><canvas id="bottomCanvas" width="356" height="358"></canvas> <!-- 底层Canvas --><canvas id="topCanvas" width="356" height="358"></canvas> <!-- 上层Canvas --></div><script>function loadImages() {var selectElement = document.getElementById('mySelect');var selectedValue = selectElement.options[selectElement.selectedIndex].value;var bottomCanvas = document.getElementById('bottomCanvas');var topCanvas = document.getElementById('topCanvas');var bottomCtx = bottomCanvas.getContext('2d');var topCtx = topCanvas.getContext('2d');// 清除画布bottomCtx.clearRect(0, 0, bottomCanvas.width, bottomCanvas.height);topCtx.clearRect(0, 0, topCanvas.width, topCanvas.height);// 加载底层图片var bottomImage = new Image();bottomImage.src = 'img/bottom' + selectedValue + '.png';bottomImage.onload = function() {bottomCtx.drawImage(bottomImage, 0, 0, bottomCanvas.width, bottomCanvas.height);};// 重新加载并绘制上层图片var topImage = new Image();topImage.src = 'img/top' + selectedValue + '.png'; // 确保这里的路径正确匹配你的图片路径和命名topImage.onload = function() {topCtx.globalCompositeOperation = 'source-over'; // 重置合成操作为默认值topCtx.drawImage(topImage, 0, 0, topCanvas.width, topCanvas.height);// 确保刮刮效果重新应用addScratchEffect(topCanvas, topCtx);};}function addScratchEffect(canvas, ctx) {var isDown = false;// 移除之前可能添加的事件监听器canvas.onmousedown = null;canvas.onmouseup = null;canvas.onmousemove = null;// 鼠标按下事件canvas.onmousedown = function() {isDown = true;ctx.globalCompositeOperation = 'destination-out'; // 设置合成操作以实现刮效果};// 鼠标松开事件canvas.onmouseup = function() {isDown = false;};// 鼠标移动事件canvas.onmousemove = function(event) {if (!isDown) return;var x = event.offsetX;var y = event.offsetY;// 绘制擦除效果ctx.beginPath();ctx.arc(x, y, 20, 0, Math.PI * 2); // 使用圆形笔触ctx.fill();};}// 页面加载完毕后初始化画布document.addEventListener('DOMContentLoaded', function() {loadImages(); // 页面加载时也加载图片});</script>
</body>
</html>

本文是对https://blog.csdn.net/cnds123/article/details/112392014 例子的补充

关于HTML5中，使用<select>元素创建一个列表框（下拉框），并使用JavaScript来操作，可参见https://blog.csdn.net/cnds123/article/details/128353007

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