2023 uniapp( vue3 + TS )使用canvas生成海报并保存，taro/微信小程序也适用

有段时间没写vue了，有点生疏了......

1、代码有注释，完整代码如下

<template><view class="page"><canvas class="canvas" v-if="isShow" :style="{width:`${canvasWidth}px`,height:`${canvasHeight}px`}":canvas-id="canvasId"></canvas><view class="tool"><u-button @click="nextImg" :custom-style="buttonCustomStyle" text="下一张"color="linear-gradient(to right, #232526, #414345)"></u-button><u-button @click="save" :custom-style="buttonCustomStyle" text="保存图片"color="linear-gradient(to right, rgb(66, 83, 216), rgb(213, 51, 186))"></u-button></view></view>
</template><script setup lang="ts">import { onMounted, reactive, ref, watch } from "vue";import { getImgBase64, drawRoundedRect, drawText, getSystemInfo } from "@/utils/canvas";import { imageList } from './utils'import type { ImageListType } from './utils'import { getAuthorize } from "@/utils";// 按钮样式const buttonCustomStyle = reactive({width: '49%',});// const color = '#f7f6ff'const offsetNumber : number = 20;const listHeight : number = 66;const context = ref(null)const pageColor = ref(imageList[0].pageColor)const canvasId = ref<string>(String(`canvasId${new Date().getTime()}`))const isShow = ref<boolean>(false)const imageObj = ref<ImageListType>(imageList[0])const imgTemp = ref<string>(wx.env.USER_DATA_PATH + `/${new Date().getTime()}-temp.png`) //图片存储的临时路径const canvasWidth = ref<number>(0)// canvas宽度const canvasHeight = ref<number>(0)// canvas宽度const canvasWidthRate = ref<number>(0.8)//canvas基于屏幕宽度占比,随便设置，我这里设置占屏幕宽度的百分之八十// 绘制图片,并转成base64const drawBgImg = async () => {// 图片临时地址重新赋值，避免图片加载路径都是一样的imgTemp.value = wx.env.USER_DATA_PATH + `/${new Date().getTime()}-temp.png`const ctx = context.valueconst { imgUrl, imageWidth, imageHeight } = await getImgBase64({src: imageObj.value.imageSrc,canvasWidth: canvasWidth.value,filePath: imgTemp.value})canvasHeight.value = canvasHeight.value + imageHeight //重新计算画布总高度// 填充背景矩阵drawRoundedRect(ctx, 0, 0, canvasWidth.value, canvasHeight.value, {fillColor: imageObj.value.bgColor,leftBottom: true,leftTop: true,rightBottom: true,rightTop: true,r: 5})// 图片如何居中呢？// 当前画布宽度 - 图片宽度 = 空出来的间隙// 图片居中 = 空出来的间隙 / 2 = x 轴起点 x = canvasWidth.value - imageWidth) / 2ctx.drawImage(imgUrl, (canvasWidth.value - imageWidth) / 2, offsetNumber, imageWidth, imageHeight);}// 绘制文字const drawTxt = async () => {const ctx = context.valueconst offsetY = canvasHeight.value// 填充矩形背景drawRoundedRect(ctx, 0, canvasHeight.value, canvasWidth.value, listHeight, {fillColor: imageObj.value.bgColor,});// 绘制文字drawText({ctx,text: imageObj.value.name,fillStyle: '#000000',fontSize: 22,x: (canvasWidth.value / 2),y: offsetY + 25,center: true})// 绘制文字drawText({ctx,text: imageObj.value.desc,fillStyle: '#000000',fontSize: 16,x: (canvasWidth.value / 2),y: offsetY + 25 + 25,center: true})//画布高度重新计算canvasHeight.value = canvasHeight.value + listHeight}// 初始化canvasconst initCanvas = async () => {try {uni.showLoading()const { windowWidth } : any = await getSystemInfo()const ctx = context.valuecanvasHeight.value = offsetNumber;//初始化高度canvasWidth.value = windowWidth * canvasWidthRate.value//初始化宽度await drawBgImg()await drawTxt()ctx.draw()} finally {uni.hideLoading()}}onMounted(() => {isShow.value = true})watch(isShow, () => {if (isShow.value) {canvasId.value = String(`canvasId${new Date().getTime()}`)//由于存在多次绘制，避免ID重复，需要重新赋值context.value = uni.createCanvasContext(canvasId.value)//由于存在多次绘制，所以每次都重新创建新的画布实例initCanvas()}})// 下一张图const nextImg = () => {isShow.value = falseimageObj.value = imageList[imageObj.value.id + 1] ?? imageList[0]pageColor.value = imageObj.value.pageColorsetTimeout(() => {isShow.value = true}, 100)}// 图片添加到相册const addIamgeToAlbum = async () => {try {const { tempFilePath } = await uni.canvasToTempFilePath({canvasId: canvasId.value,});console.log('tempFilePath', tempFilePath);await uni.saveImageToPhotosAlbum({filePath: tempFilePath})uni.showToast({title: '保存成功！'})} catch {}}// 保存const save = async () => {try {uni.showLoading()// 获取用户设置const { authSetting } = await uni.getSetting()// 没有权限的时候if (!authSetting['scope.writePhotosAlbum']) {await getAuthorize('scope.writePhotosAlbum', {title: '请授权保存到相册',callback: addIamgeToAlbum})return}addIamgeToAlbum()} catch (err) {} finally {uni.hideLoading()}}
</script><style lang="scss" scoped>.page {background-color: v-bind(pageColor);height: 100vh;overflow: hidden;.canvas {margin: 20px auto 0;}.tool {width: 100%;display: flex;align-items: center;justify-content: center;position: fixed;bottom: 0;left: 0;right: 0;}}
</style>

1.1、工具函数 - canvas.ts

//utils/canvas.ts
const fs = uni.getFileSystemManager()// 将Base64写入本地文件
const base64WriteFile = (filePath : string, data : string) => {return new Promise((resolve, reject) => {fs.writeFile({filePath,data,encoding: 'base64',success: (res) => {resolve(res);},fail: (err) => {reject(err);},});});
};
// 参数的类型校验
type GetImgBase64Type = {src : string;//图片地址(本地/在线地址)canvasWidth : number;//画布宽度filePath : string//临时路径
}
// 加载图片地址，生成base64并写入临时路径中
export const getImgBase64 = async (params : GetImgBase64Type) => {const { src, canvasWidth, filePath } = paramstry {// 获取图片信息：地址、宽高const imgInfo = await uni.getImageInfo({src,});// 计算图片在画布中的宽度const imageWidth = canvasWidth * 0.8;//随便定的，多少px都行// // 根据比例计算图片在画布中的高度const scaleFactor = Number((imageWidth / imgInfo.width).toFixed(2));// 根据比例计算图片高度const imageHeight = imgInfo.height * scaleFactor;// 生成base64const base64 : any = fs.readFileSync(imgInfo.path, 'base64')// 写入本地await base64WriteFile(filePath, base64)const currentImgInfo = await uni.getImageInfo({src: filePath,});return {imageWidth,imageHeight,imgUrl: currentImgInfo.path}} catch (err) {console.log('err', err);}};type DrawRoundedRectParamsType = {leftTop ?: boolean;leftBottom ?: boolean;rightTop ?: boolean;rightBottom ?: boolean;fillColor ?: string;r ?: number;
};
// canvas 绘制自定义圆角矩形
export const drawRoundedRect = (ctx : any,x : number,y : number,w : number,h : number,params ?: DrawRoundedRectParamsType,
) => {const {leftTop = false,leftBottom = false,rightTop = false,rightBottom = false,fillColor = 'transparent',r = 0,} = params || {};ctx.save(); // 保存当前绘图状态 防止虚线影响其他图形ctx.beginPath();ctx.setFillStyle(fillColor);ctx.setStrokeStyle('transparent');ctx.moveTo(x + r, y);// 绘制上边线和左上角圆弧if (leftTop) {ctx.arc(x + r, y + r, r, Math.PI, Math.PI * 1.5);ctx.lineTo(x, y);} else {ctx.moveTo(x, y + r);ctx.lineTo(x, y);ctx.lineTo(x + r, y);}ctx.lineTo(x + w - r, y);// 绘制上边线和右上角圆弧if (rightTop) {ctx.arc(x + w - r, y + r, r, Math.PI * 1.5, Math.PI * 2);} else {ctx.lineTo(x + w - r, y);ctx.lineTo(x + w, y);ctx.lineTo(x + w, y + r);}ctx.lineTo(x + w, y + h - r);// 绘制下边线和右下角圆弧if (rightBottom) {ctx.arc(x + w - r, y + h - r, r, 0, Math.PI * 0.5);} else {ctx.lineTo(x + w, y + h - r);ctx.lineTo(x + w, y + h);ctx.lineTo(x + w - r, y + h);}ctx.lineTo(x + r, y + h);// 绘制下边线和左下角圆弧if (leftBottom) {ctx.arc(x + r, y + h - r, r, Math.PI * 0.5, Math.PI);} else {ctx.lineTo(x + r, y + h);ctx.lineTo(x, y + h);ctx.lineTo(x, y + h - r);}ctx.lineTo(x, y + r);// 绘制左边线和左上角圆弧if (leftTop) {ctx.arc(x + r, y + r, r, Math.PI, Math.PI * 1.5);ctx.moveTo(x + r, y);} else {ctx.moveTo(x, y + r);ctx.lineTo(x, y);ctx.lineTo(x + r, y);}ctx.fill();ctx.closePath();ctx.stroke();ctx.restore(); // 恢复之前的绘图状态
};
type DrawTextConfigType = {ctx : any;fillStyle : string;//填充颜色fontSize : number//文字大小text : string;//在画布上输出的文本x : number;//绘制文本的左上角x坐标位置y : number//绘制文本的左上角y坐标位置center ?: boolean
}
// 绘制文本
export const drawText = (config : DrawTextConfigType) => {const { fillStyle, fontSize, x, y, text, ctx, center = false } = configctx.setFillStyle(fillStyle);ctx.setFontSize(fontSize);if (center) {ctx.textAlign = 'center';//文字水平居中}ctx.fillText(text, x, y);
}
// 获取当前设备信息
export const getSystemInfo = () => {return new Promise((resolve) => {uni.getSystemInfo({success(res) {resolve(res)},})})
}

1.2、工具函数 - index.ts

//utils/index.ts
// 获取用户授权
type GetAuthorizeType = {title ?: string;//授权弹框描述callback ?: () => void//成功的回调
}
export const getAuthorize = (scope : string, params : GetAuthorizeType) => {const { title = '请开启授权', callback } = paramsreturn new Promise(() => {uni.authorize({scope,success: () => {callback?.()},fail: () => {// 如果用户点了拒绝，需要弹框提示再次授权uni.showModal({title,success() {uni.openSetting();},});}})})
}

1.3、图片列表函数

// ./utils/index.ts
export type ImageListType = {id : number;name : stringdesc : stringimageSrc : stringbgColor : stringpageColor : string
}
export const imageList : ImageListType[] = [{id: 0,name: '那维莱特',desc: '潮水啊，我已归来！',imageSrc: '../../static/那维莱特.jpg',bgColor: '#b2d4ff',pageColor: '#d9e9ff',},{id: 1,name: '东方镜',desc: '太阳之下，诸世皆影！',imageSrc: '../../static/镜.jpg',bgColor: '#ffdecd',pageColor: '#fff3ed',},{id: 2,name: '魈',desc: '你去吧,我会在这里等你。',imageSrc: '../../static/魈.png',bgColor: '#f1ddff',pageColor: '#fbf4ff',},{id: 3,name: '琴团长',desc: '我以此剑起誓，必将胜利献给你！',imageSrc: '../../static/琴.jpg',bgColor: '#e6e4ff',pageColor: '#f7f6ff',},
]

2、效果如下

3、添加相册授权

根据各自框架添加授权即可，比如uniapp在manifest.json下

    "mp-weixin" : {"appid" : "你的微信appid","setting" : {"urlCheck" : false},"usingComponents" : true,/* 授权 */"permission": {"scope.writePhotosAlbum": {"desc": "请授权保存到相册"}}},

4、项目地址

我的项目地址，点击跳转

5、问题总汇

5.1、为什么本地图片/在线图片真机不显示等？

将所有用到的图片转 base64 展示，参考上面工具函数中的 getImgBase64()

5.2、多文本如何换行？

参考下面地址使用canvas画布时多行文本应该怎么换行？ | 微信开放社区

5.3、多次绘制出现白屏等？

比如以弹框的形式多次点击生成等情况，首先要确保每个canvas-idID的实例不能重复。可以参考我上面标题1中的代码。

5.4、当ctx.draw()后需要立马回去临时路径做 image预览时，画布生成的内容不全？

5.4.1、前提情景

由于 canvas 的层级比较高，做预览的时候会遮住其他的view等标签。而且样式或拖拽等也不好处理，花费时间肯定更多一点，这个时候需要用 <image src="图片的临时路径" mode=""></image> 代替 canvas 做展示。

5.4.2、解决

改写ctx.draw()为如下：

		ctx.draw(false,setTimeout(async () => {//在这里生成临时路径const { tempFilePath } = await uni.canvasToTempFilePath({canvasId: canvasId.value,});console.log('tempFilePath', tempFilePath);await uni.saveImageToPhotosAlbum({filePath: tempFilePath})}, 100),);

由于绘制可能需要更长的时间，通过延时器即可解决。