为什么要在服务端装canvas? 因为并不是所有的客户端都能很好的支持canvas(比如微信小程序不能修改自定义字体),所以我们需要一个
能够在服务端生成图片的,然后将图片传输

安装node-canvas

1. 更新编译环境

sudo apt-get install libcairo2-dev libjpeg8-dev libpango1.0-dev libgif-dev build-essential g++ -y

2. 安装node-canvas

npm install -g canvas

3. 测试代码

var Canvas = require('canvas'),
canvas = new Canvas(300, 200),
ctx = canvas.getContext('2d'),
fs = require('fs');

var out = fs.createWriteStream(__dirname + '/image.png')
, stream = canvas.createPNGStream();

stream.on('data', function(chunk){
out.write(chunk);
});

//在左边画正方形
ctx.fillStyle = '#A00'
ctx.fillRect(0, 30,50,50);


//在右边画正方形
ctx.fillStyle = '#aaa'
ctx.fillRect(50, 30, 50, 50);

//画文字
ctx.fillStyle = "#000";
ctx.font = "20px Arial";
ctx.fillText("Hello World", 0, 20);

//画一个圆
ctx.beginPath();
ctx.arc(30, 110, 20, 0, 2*Math.PI);
ctx.stroke();
ctx.fillStyle = "green";
ctx.fill();
ctx.save();

可能遇到的问题

如果你按上述方法操作,并且运行成功了。那便是极好的

1. 自定义字体

// You need to call it before the Canvas is created
Canvas.registerFont('comicsans.ttf', {family: 'Comic Sans'});

var canvas = new Canvas(500, 500),
ctx = canvas.getContext('2d');

ctx.font = '12px "Comic Sans"';
ctx.fillText(250, 10, 'Everyone hates this font :(');

不过可能会发现Canvas.registerFont is not a function这是因为npm版本的没有这个函数。

所以你需要去找另一个github版https://github.com/chearon/node-canvas#12971f64a66b

git clone 下来

然后将Canvas = require(‘canvas’)改成require(‘./node-canvas’),
var canvas = new Canvas(300, 200)改成var canvas = new Canvas.Canvas(300, 200)

2. Error: Cannot find module ‘../build/Release/canvas.node’

如果遇到这个问题,请cd进你的node-canvas目录执行npm install

如果还是不行,请执行npm install -g node-gyp

然后再cd项目目录执行node-gyp rebuild,then cd 进node-canvas同样执行node-gyp rebuild

如果成功则会出现

编译过程

示例代码

我的项目目录

.
├── 1.html
├── composer.json
├── font
├── fz.ttf
├── img
├── index.js
├── node-canvas
├── node_modules
├── package.json
└── package-lock.json

我的代码

var fs = require('fs'),path = require('path');
var http = require('http'),url = require("url");
var Canvas = require('./node-canvas'),Image = Canvas.Image;
var Fonts = [];
var filePath = path.resolve('./font');

let promise = new Promise(function(resolve, reject) {
let i=0;
fs.readdir(filePath,function(err,files){
if(err){
console.warn(err)
}else{
files.forEach(function(filename){
Canvas.registerFont(filePath + "/" + filename, {family: "font" + i});
console.log(i);
i++;
});
}
});

});

promise.then(function() {
console.log("ASDF");
Fonts.forEach((Element) =>{
console.log(Element);
});
});

console.log('Hi!');


http.createServer(function (req, res) {
var params = url.parse(req.url, true).query;
var str = params.str + '\r',site = params.site;
var row = 1,col = 15,width = 1500;
row = str.length / 15 + 1;
var fontsize = width/col;
var height = fontsize * row + 200;
if(height < 1000){height = 1000}
var canvas = new Canvas.Canvas(width, height), ctx = canvas.getContext('2d')
res.writeHead(200,{"Content-Type": "image/png"});
ctx.fillStyle = '#FFF';
ctx.fillRect(0,0,canvas.width, canvas.height);
ctx.fillStyle = '#000';
if(row < 2){
let num = str.length
fontsize = 1200 / num;
ctx.font = fontsize + 'px "font'+ site +'"';
ctx.fillText(str,( width - num * fontsize ) / 2, (height-fontsize)/2 -200 + fontsize);
}
else{
ctx.font = fontsize + 'px "font'+ site +'"';
for(let i = 0;i < row ; i++){
ctx.fillText(str.substring(i*15,(i+1)*15), 0, fontsize*(i+1));
}
}

fs.readFile(__dirname + '/img/brand.png', function(err, squid){
if (err) throw err;
img = new Image;
img.src = squid;
ctx.fillStyle = '#42b983';
ctx.fillRect(0,canvas.height - 230,canvas.width, 230);
ctx.drawImage(img, canvas.width - img.width / 2 - 50, canvas.height - img.height / 2 - 50, img.width / 2, img.height / 2);
res.end(canvas.toBuffer());
});
}).listen(8080);

效果展示

天地玄黄