无法使用webpack dev服务器在nodejs中加载图像 [英] Cannot load image using webpack dev server in nodejs

问题描述

您好我使用以下代码尝试为我的游戏绘制背景，但我一直收到失败消息，我不知道为什么会发生这种情况。

Hi I am using the following code to try to draw a background for my game, but I keep getting the failure message and I couldn't figure out why this would happen.

这是我的 main.js ：

this.background = new Image();

var context = document.getElementById('canvas').getContext('2d');

var loaded = false;

var drawBackground = function () {

  loaded = true;

  var pattern = context.createPattern(this.background, 'repeat');
  context.fillStyle = pattern;
  context.fillRect(0, 0, 10000, 10000);
}

this.background.onload = drawBackground;
this.background.src = "../images/bg.jpg";

setTimeout(function() {
  if (loaded) {
    console.log('success');
  } else {
    console.log('falilure');
  }
}, 3000);

我的文件目录结构如下：

My file directory structure looks like this:

- dist
  - static
    - bg.jpg
  - bundle.js
- images
   - bg.jpg
- src
  - main.js
- server.js

我已尝试将 this.background.src 更改为 ./ static / bg.jpg ，但它仍然不工作。

I have tried changing this.background.src to ./static/bg.jpg but it still doesn't work.

我使用命令 npm run dev 在webpack-dev服务器上运行我的代码。在生产中，源代码和静态文件将被复制并捆绑到 dist 目录中。但我使用的开发模式，所以我猜，图像还没有复制。为什么我的图片未加载？

I am running my code on a webpack-dev-server using the command npm run dev. In production the source code and static files will be copied and bundled to dist directory. But I am using the development mode so I guess the image is not copied yet. Why is my image not loaded?

推荐答案

我已经找到了解决方案，我在我的代码中犯了几个错误。

I have found the solution for this after tweaking for a day. I have made several mistakes in my code.

要在webpack-dev-server中加载镜像，我们需要使用webpack.config.js中配置的加载器

To load the image in webpack-dev-server we need to use loaders configured in webpack.config.js (or whatever name you give to the config file of webpack-dev-server).

所以我把加载器定义放在模块部分中，如下所示：

So I put the loader definition inside the module section like this:

module: {
    loaders: [
      {
        test: /\.js$/,
        loader: 'babel',
        include: path.join(__dirname, 'src')
      },
      { test: /\.(png|jpg)$/, loader: 'url-loader?limit=90000' } 
    ]
  },

来到棘手的部分，单独使用加载器不会得到你的图像显示。您必须要求它作为JavaScript代码中的资源。因此，在问题代码中，我需要更改

Now here comes the tricky part, using the loader alone doesn't get your image displayed. You have to require it as a resource in javascript code. So in the question code I need to change

this.background.src = "../images/bg.jpg";

：

this.background.src = require('../images/bg.jpg');

但是这还是不行，因为我在同步模型上使用异步调用。
我需要更改onload调用以接收回调并在回调中绘制图像。然后代码终于工作。它看起来像这样：

But that still doesn't work, because I was using async calls on synchronous model. I need to change the onload call to receive a callback and draw images in the callback. Then the code finally works. And it would look like this:

var image = this.background;
var _canvas = document.getElementById('canvas');
this.ctx = _canvas.getContext('2d');
var drawBackground = function (callback) {      
      callback(this);
}

image.onload = drawBackground(() => {
  let pattern = this.ctx.createPattern(image, 'repeat');
  this.ctx.fillStyle = pattern;
  this.ctx.fillRect(0, 0, _canvas.width, _canvas.height);
});
image.src = require('../images/bg.jpg'); 

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