直接上组件封装

<template>
    <div class="sd-water-mark" ref="sdWaterMark">
        <slot></slot>
    </div>
</template>

<script>
    export default {
        props: {
            text: { type: String, required: true, default: "" },
            subtext: { type: String, default: "" },
            color: { type: String, default: "rgba(128,128,128,0.2)" }
        },
        data() {
            return {

            }
        },
        mounted() {
            this.create()
        },
        methods: {
            create(){
                this.clear()
                //创建画板
                var canvas = document.createElement('canvas')
                canvas.width = 150
                canvas.height = 150
                canvas.style.display = 'none'
                //绘制文字
                var text = canvas.getContext('2d')
                text.rotate(-45 * Math.PI / 180)
                text.translate(-75, 25)
                text.fillStyle = this.color
                text.font = "normal 20px SimHei"
                text.textAlign = "center"
                text.fillText(this.text, canvas.width / 2, canvas.height / 2)
                text.font = "14px Microsoft YaHei"
                text.fillText(this.subtext, canvas.width / 2, canvas.height / 2 + 20)
                //创建水印容器
                var watermark = document.createElement('div')
                watermark.setAttribute('class', 'watermark')
                const styleStr = `position:absolute;top:0;left:0;right:0;bottom:0;z-index:99;pointer-events:none;background-repeat:repeat;background-image:url('${canvas.toDataURL("image/png")}');`
                watermark.setAttribute('style', styleStr);
                this.$refs.sdWaterMark.appendChild(watermark)
            },
            clear(){
                var wmDom = this.$refs.sdWaterMark.querySelector('.watermark')
                wmDom && wmDom.remove()
            }
        }
    }
</script>

<style scoped>
    .sd-water-mark {position: relative;display: inherit;width: 100%;height: 100%;}
</style>

组件使用

<sd-water-mark text="我是主" subtext="我是副标题">
  // 包裹需要使用到水印的组件
</sd-water-mark>

效果

image.png