水印项目的实现以及两种实现方案的选优

水印项目我们提出了两种解决方案

一、用shadow dom实现

1、基本思路

通过 attachShadow 这个方法生成一个shadow root 即shadow的根节点，然后在这个根节点下面通过循环语句添加水印，利用position为absolute进行排版，使其铺满容器

 show me the code：

(function (root, factory) {
    if (typeof define === 'function' && define.amd) {
        /*AMD. Register as an anonymous module.
        *define([], factory); */
        define([], factory());
    } else if (typeof module === 'object' && module.exports) {
        /*Node. Does not work with strict Commonjs, but
        // only Commonjs-like environments that support module.exports,
        // like Node.*/
        module.exports = factory();

    } else {
        /*Browser globals (root is window)*/
        root['watermark'] = factory();
    }
}(this, function () {

    /*Just return a value to define the module export.*/
    let watermark = {};

    /*加载水印*/
    let loadMark = function () {
        let defaultSettings = {
            watermark_id: 'wm_div_id',          //水印总体的id
            watermark_prefix: 'mask_div_id',    //小水印的id前缀
            watermark_txt: "测试水印",             //水印的内容
            watermark_x: 20,                     //水印起始位置x轴坐标
            watermark_y: 40,                     //水印起始位置Y轴坐标
            watermark_rows: 0,                   //水印行数
            watermark_cols: 0,                   //水印列数
            watermark_x_space: 100,              //水印x轴间隔
            watermark_y_space: 50,               //水印y轴间隔
            watermark_font: '微软雅黑',           //水印字体
            watermark_color: 'black',            //水印字体颜色
            watermark_fontsize: '18px',          //水印字体大小
            watermark_alpha: 0.15,               //水印透明度，要求设置在大于等于0.005
            watermark_ 100,                //水印宽度
            watermark_height: 100,               //水印长度
            watermark_angle: 15,                 //水印倾斜度数
            watermark_parent_selector: null,  //水印插件挂载的父元素选取器,不输入则默认挂在body上
            need_adapt_screen: false,     // 是否根据屏幕的分辨率等比变化每个水印的宽度和字体大小
            watermark_width_proportion: 15, // 每个水印宽度自适应屏幕变化的等比放大或缩小的值
            watermark_fontsize_proportion: 95, // 每个水印字体大小自适应屏幕变化的等比放大或缩小的值
        };
        let watermark_parent_node = null  //水印插件挂载的父元素element,不输入则默认挂在body上

        let setting = arguments[0] || {};
        /*采用配置项替换默认值，作用类似jquery.extend*/
        if (arguments.length === 1 && typeof arguments[0] === "object") {
            for (let key in setting) {
                if (setting[key] && defaultSettings[key] && setting[key] === defaultSettings[key]) continue;
                /*veronic: resolution of watermark_angle=0 not in force*/
                else if (setting[key] || setting[key] === 0) defaultSettings[key] = setting[key];
            }
        }

        /* 设置水印的容器 */
        if (defaultSettings.watermark_parent_selector) {
            watermark_parent_node = document.querySelector(defaultSettings.watermark_parent_selector)
        } else {
            watermark_parent_node = document.body
        }

        /*如果元素存在则移除*/
        let watermark_element = document.getElementById(defaultSettings.watermark_id);
        if (watermark_element) {
            let _parentElement = watermark_element.parentNode;
            if (_parentElement) {
                _parentElement.removeChild(watermark_element);
            }
        }
        
        /*获取水印的起始位置*/
        let page_offsetTop = 0;
        let page_offsetLeft = 0;
        page_offsetTop = watermark_parent_node.offsetTop || 0;
        page_offsetLeft = watermark_parent_node.offsetLeft || 0;
        page_width = watermark_parent_node.offsetWidth - defaultSettings.watermark_width / 2 || 0;
        page_height = (Math.max(watermark_parent_node.offsetHeight, watermark_parent_node.scrollHeight) - defaultSettings.watermark_height / 2) || 0;
        defaultSettings.watermark_x = defaultSettings.watermark_x + page_offsetLeft;
        defaultSettings.watermark_y = defaultSettings.watermark_y + page_offsetTop;

        /*创建水印外壳div*/
        let otdiv = document.getElementById(defaultSettings.watermark_id);
        let shadowRoot = null;

        if (!otdiv) {
            otdiv = document.createElement('div');

            /*创建shadow dom*/
            otdiv.id = defaultSettings.watermark_id;
            otdiv.style.pointerEvents = "none";

            /*判断浏览器是否支持attachShadow方法*/
            if (typeof otdiv.attachShadow === 'function') {
                shadowRoot = otdiv.attachShadow({mode: 'open'});
            } else if (typeof otdiv.createShadowRoot === 'function') {
                shadowRoot = otdiv.createShadowRoot();
            } else {
                shadowRoot = otdiv;
            }

            watermark_parent_node.appendChild(otdiv)

        } else if (otdiv.shadowRoot) {
            shadowRoot = otdiv.shadowRoot;
        }

        // shadow内加个容器
        let shadowOutDiv = document.createElement('div')
        shadowOutDiv.id = 'shadowContainer'
        shadowRoot.appendChild(shadowOutDiv)


        /*如果将水印列数设置为0，或水印列数设置过大，超过页面最大宽度，则重新计算水印列数和水印x轴间隔*/
        if (defaultSettings.watermark_cols == 0 || (parseInt(defaultSettings.watermark_x + defaultSettings.watermark_width * defaultSettings.watermark_cols + defaultSettings.watermark_x_space * (defaultSettings.watermark_cols - 1)) > page_width)) {
            defaultSettings.watermark_cols = parseInt((page_width - defaultSettings.watermark_x + page_offsetLeft) / (defaultSettings.watermark_width + defaultSettings.watermark_x_space));
            defaultSettings.watermark_x_space = parseInt((page_width - defaultSettings.watermark_x + page_offsetLeft - defaultSettings.watermark_width * defaultSettings.watermark_cols) / (defaultSettings.watermark_cols - 1));
        }
        /*如果将水印行数设置为0，或水印行数设置过大，超过页面最大长度，则重新计算水印行数和水印y轴间隔*/
        if (defaultSettings.watermark_rows == 0 || (parseInt(defaultSettings.watermark_y + defaultSettings.watermark_height * defaultSettings.watermark_rows + defaultSettings.watermark_y_space * (defaultSettings.watermark_rows - 1)) > page_height)) {
            defaultSettings.watermark_rows = parseInt((page_height - defaultSettings.watermark_y + page_offsetTop) / (defaultSettings.watermark_height + defaultSettings.watermark_y_space));
            defaultSettings.watermark_y_space = parseInt(((page_height - defaultSettings.watermark_y + page_offsetTop) - defaultSettings.watermark_height * defaultSettings.watermark_rows) / (defaultSettings.watermark_rows - 1));
        }

        let x;
        let y;
        for (let i = 0; i < defaultSettings.watermark_rows; i++) {
            y = defaultSettings.watermark_y + (defaultSettings.watermark_y_space + defaultSettings.watermark_height) * i;
            for (let j = 0; j < defaultSettings.watermark_cols; j++) {
                x = defaultSettings.watermark_x + (defaultSettings.watermark_width + defaultSettings.watermark_x_space) * j;

                let mask_div = document.createElement('div');
                let oText = document.createTextNode(defaultSettings.watermark_txt);
                mask_div.appendChild(oText);
                /*设置水印相关属性start*/
                mask_div.id = defaultSettings.watermark_prefix + i + j;
                /*设置水印div倾斜显示*/
                mask_div.style.webkitTransform = "rotate(-" + defaultSettings.watermark_angle + "deg)";
                mask_div.style.MozTransform = "rotate(-" + defaultSettings.watermark_angle + "deg)";
                mask_div.style.msTransform = "rotate(-" + defaultSettings.watermark_angle + "deg)";
                mask_div.style.OTransform = "rotate(-" + defaultSettings.watermark_angle + "deg)";
                mask_div.style.transform = "rotate(-" + defaultSettings.watermark_angle + "deg)";
                mask_div.style.visibility = "";
                mask_div.style.position = "absolute";
                /*选不中*/
                mask_div.style.left = x + 'px';
                mask_div.style.top = y + 'px';
                mask_div.style.overflow = "hidden";
                mask_div.style.zIndex = "9999999";
                mask_div.style.opacity = defaultSettings.watermark_alpha;
                mask_div.style.fontSize = defaultSettings.watermark_fontsize;
                mask_div.style.fontFamily = defaultSettings.watermark_font;
                mask_div.style.color = defaultSettings.watermark_color;
                mask_div.style.textAlign = "center";
                mask_div.style.width = defaultSettings.watermark_width + 'px';
                mask_div.style.height = defaultSettings.watermark_height + 'px';
                mask_div.style.display = "block";
                mask_div.style['-ms-user-select'] = "none";
                /*设置水印相关属性end*/
                shadowOutDiv.appendChild(mask_div);

            }
        }
    };

    /*初始化水印，添加load和resize事件*/
    watermark.init = function (settings) {
        window.addEventListener('load', function () {
            loadMark(settings);
        });
        window.addEventListener('resize', function () {
            loadMark(settings);
        });
        window.addEventListener('DOMContentLoaded', function () {
            loadMark(settings);
        });

    };

    /*手动加载水印*/
    watermark.load = function (settings) {
        loadMark(settings);
        observerDomReloadMark(settings)
    };

    return watermark;
}))

2、优化

但是毕竟水印是有关安全方面的，如果别人打开开发者模式很轻松的就水印的内容更改甚至完全删除，所以不能就这么完事了。我们需要监听DOM的变化，判断如果用户通过开发者工具手动修改了水印的dom，我们就重新渲染水印，实现水印不能手动进行了修改。

思路：通过mutationObsever监听DOM的变化，判断是否是水印部分的dom 变化，如果是则重新渲染

show me the code:

/* 监听DOM的变化，防止手动删除 */
    let observerDomReloadMark = (settings) => {
        // Select the node that will be observed for mutations
        let observer_node = document.querySelector('#shadowContainer')
        // Options for the observer (which mutations to observe)
        let config = {
            attributes: true,
            childList: true,
            subtree: true
        };
        // Callback function to execute when mutations are observed
        const mutationCallback = (mutationsList) => {
            // for (let mutation of mutationsList) {
            //     let type = mutation.type;
            //     switch (type) {
            //         case "childList":
            //             console.log("A child node has been added or removed.");
            //             break;
            //         case "attributes":
            //             console.log(`The ${mutation.attributeName} attribute was modified.`);
            //             break;
            //         case "subtree":
            //             console.log(`The subtree was modified.`);
            //             break;
            //         default:
            //             break;
            //     }
            // }
            // loadMark(settings)
            console.log(2222)
        };

        // Create an observer instance linked to the callback function
        let observer = new MutationObserver(mutationCallback);

        // Start observing the target node for configured mutations
        observer.observe(observer_node, config);

        // Later, you can stop observing
        // observer.disconnect();
    }

这个方法看起来完美，然而现实很残酷，当我们再浏览器中看效果的时候发现mutationObsever不能监听shadow的变化，what? 查资料后发现shadow是独立于dom树的，相当于被隔离起来的dom。既然如此那就放弃装逼吧，还是老老实实用正常的dom实现吧，有多少个水印就生成多个水印的dom，这必要会导致性能问题。好吧，我们还是再另寻他法。

二、canvas绘图

1、基本思路

通过canvas把单个水印绘制出来，用toDataURL方法生成图片的base64编码，放在水印容器的background-image：url()里面，背景图片会自动铺满整个容器。思想比第一种方案简单很多。

show me the code:

      var canvas = document.createElement('canvas')
      canvas.id = 'canvas'
      canvas.width = defaultSettings.watermark_width // 单个水印的宽度
      canvas.height = defaultSettings.watermark_height // 单个水印的高度
      var ctx = canvas.getContext('2d')
      ctx.font = 'normal 12px Microsoft Yahei' // 设置样式
      ctx.fillStyle = 'rgba(112, 113, 114, 0.2)' // 水印字体颜色
      ctx.translate(canvas.width/2,canvas.height/2)
      ctx.rotate((defaultSettings.watermark_angle * Math.PI) / 180) // 水印偏转角度
      ctx.translate(-canvas.width/2,-canvas.height/2)
      ctx.fillText(defaultSettings.watermark_txt, 30, 20)
      var src = canvas.toDataURL('image/png')

      /* 设置水印的容器 */
      var watermark_parent_node = null
      if (defaultSettings.watermark_parent_selector) {
          watermark_parent_node = document.querySelector(defaultSettings.watermark_parent_selector)
      } else {
          watermark_parent_node = document.body
      }
     watermark_parent_node.style.pointerEvents = 'none'
      // 判断容器是否已经设置了backgroundImage属性值
      if (!watermark_parent_node.style.backgroundImage) {
          watermark_parent_node.style.backgroundImage = 'URL(' + src + ')'
      } else {
          watermark_parent_node.style.backgroundImage = watermark_parent_node.style.backgroundImage + ', URL(' + src + ')'
      }

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2、优化

优化思路和第一种方案一样，只不过这种方案的好处就是可以直接监听到变化。

三、两种方案的对比

方案	优点	缺点
shadow DOM	1、低耦合，shadow dom与原先的DOM树隔离，不会影响到系统本有的功能。	1、shadow DOM不能够被监听到 2、水印文案及DOM被篡改的成本较低 3、实现逻辑比较复杂
canvas绘图	1、实现逻辑比较清晰 2、水印数据生成图片，用户想篡改比较难 3、水印被篡改能够被监听到	1、水印图片是被放在background-image里面的，如果原先在class里面设置了background-image属性的话会被覆盖掉