canvas绘制刮涂层抽奖效果

不念不忘少年蓝@ 2024-02-21 10:38 75阅读 0赞

实现的效果：主要用到画布设置图层覆盖效果globalCompositeOperation属性

![1fb6e597824e46e6a792f1d90c802a88.png][]

实现的源代码：

<!DOCTYPE html>
    <html lang="en">
        <head>
            <meta charset="UTF-8" />
            <meta name="viewport" content="width=device-width, initial-scale=1.0" />
            <title>刮刮卡抽奖效果</title>
            <style>
                * {
                    padding: 0;
                    margin: 0;
                }
                #app {
                    width: 600px;
                    height: 400px;
                    line-height: 400px;
                    text-align: center;
                }
    
                #myCanvas {
                    position: fixed;
                    top: 0;
                    left: 0;
                    z-index: 9;
                }
            </style>
        </head>
        <body>
            <div id="app">恭喜你中奖iPhone</div>
            <canvas id="myCanvas" width="600" height="400"></canvas>
            <script>
                var canvas = document.getElementById('myCanvas')
                var context = canvas.getContext('2d')
                // 画一个刮奖图层
                context.fillStyle = '#aaa'
                context.fillRect(0, 0, canvas.width, canvas.height)
                context.font = '30px Arial'
                context.fillStyle = 'red'
                context.fillText('刮开图层抽奖', 230, 200)
                // 设置一个变量
                let flag = false
    
                // 鼠标按下将变量设置为true
                canvas.onmousedown = function () {
                    flag = true
                }
    
                // 鼠标抬起将变量设置为false
                canvas.onmouseup = function () {
                    flag = false
                }
    
                // 鼠标移动
                canvas.onmousemove = function (e) {
                    // 获取鼠标在画布中的位置
                    var x = e.offsetX
                    var y = e.offsetY
                    // 判断鼠标是否在刮奖区域内
                    if (flag) {
                        // 设置图层覆盖模式
                        context.globalCompositeOperation = 'destination-out'
                        // 绘制一个矩形
                        context.fillStyle = '#fff'
                        context.fillRect(x - 10, y - 10, 20, 20)
                    }
                }
            </script>
        </body>
    </html>

[1fb6e597824e46e6a792f1d90c802a88.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/21/6db2ecdc1cde4f28a29c845b7725aa2b.png