Fabric.JS 和 Node.JS - 导出为 PNG/JPEG

Question

所以我只是在 Fabric.JS Node.JS，而不是网络，我已经设法制作了静态 Canvas，然后在上面放一个矩形。导出时间。这是我创建 canvas 和添加矩形的代码：

var canvas = new fabric.StaticCanvas(null, {width: 200, height: 200})
var rect = new fabric.Rect({
  left: 100,
  top: 100,
  width: 100,
  height: 50,
  fill: "red"
})
canvas.add(rect)

以下是我为导出图像所做的所有尝试：

//Creates a PNG file that isn't generated correctly. It's as if it's corrupt. No program can open it
canvas.createPNGStream().on("data", function (chunk) {
  fs.createWriteStream(__dirname + "/output.png").write(chunk)
})

//Causes a crash
canvas.createJPEGStream().on("data", function (chunk) {
  fs.createWriteStream(__dirname + "/output.jpeg").write(chunk)
})

Error:
C:\Users\me\Documents\my project\node_modules\canvas\lib\jpegstream.js:44
    canvas[method](options.bufsize, options.quality, options.progressive, function(err, chunk){
                  ^

TypeError: canvas[method] is not a function
    at C:\Users\me\Documents\my project\node_modules\canvas\lib\jpegstream.js:44:19
    at _combinedTickCallback (internal/process/next_tick.js:131:7)
    at process._tickCallback (internal/process/next_tick.js:180:9)

//Same thing as first try^^, except it's a JPEG
canvas.createJPEGStream({quality: 100}).pipe(fs.createWriteStream(__dirname + "/output.jpeg"))

//This one makes the PNG file, but when it's opened, its 100% transparent. That's it. The rectangle I added isn't there. Canvas size is correct, however
canvas.createPNGStream().pipe(fs.createWriteStream(__dirname + "/output.png"))

注意：fabric.Canvas(null, {width: 200, height: 200}) 似乎也与 StaticCanvas 完全相同，在本例中为

注2：此代码：

var canvas = new fabric.createCanvasForNode(200, 200)

导致此错误：

var canvas = new fabric.createCanvasForNode(200, 200)
             ^

TypeError: fabric.createCanvasForNode is not a constructor
    at Client.client.on.message (C:\Users\me\Documents\my project\index.js:31:14)
    at emitOne (events.js:115:13)
    at Client.emit (events.js:210:7)
    at MessageCreateHandler.handle (C:\Users\me\Documents\my project\node_modules\discord.js\src\client\websocket\packets\handlers\MessageCreate.js:9:34)
    at WebSocketPacketManager.handle (C:\Users\me\Documents\my project\node_modules\discord.js\src\client\websocket\packets\WebSocketPacketManager.js:103:65)
    at WebSocketConnection.onPacket (C:\Users\me\Documents\my project\node_modules\discord.js\src\client\websocket\WebSocketConnection.js:330:35)
    at WebSocketConnection.onMessage (C:\Users\me\Documents\my project\node_modules\discord.js\src\client\websocket\WebSocketConnection.js:293:17)
    at WebSocketClient.internalOnMessage (C:\Users\me\Documents\my project\node_modules\uws\uws.js:103:17)
    at native.client.group.onMessage (C:\Users\me\Documents\my project\node_modules\uws\uws.js:57:15)

我在这里遗漏了什么吗？ None 这些方法似乎都有效，这是我在 Google 上所能找到的所有方法。导出图像的正确方法是什么？它可以是 PNG 或 JPEG/JPG，最好是 PNG，但 JPEG/JPG 也可以。真的是任何常见格式。

Answer 1

找到答案了。 canvas.createPNGStream().pipe(fs.createWriteStream(__dirname + "/output.png")) 确实有效。它完全为空的原因是因为它看起来 canvas.add() 不是一个即时动作。在输出文件之前，我所做的只是 setTimeout() 来解决这个问题。希望这对某人有所帮助！

Answer 2

我使用了 node-canvas 中的示例代码并且它有效

const fs = require('fs')
const out = fs.createWriteStream(__dirname + '/test.png')
const stream = canvas.createPNGStream()
stream.pipe(out)
out.on('finish', () =>  console.log('The PNG file was created.'))

Fabric.JS 和 Node.JS - 导出为 PNG/JPEG

Fabric.JS with Node.JS - Exporting as PNG/JPEG

javascript

png

fs

node.js

fabricjs