Danmaku

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Danmaku is a JavaScript library to display flying comments on HTML media elements (video and audio). It can also display comments to your container in real time without timeline.

Installation

npm install danmaku

// Full version
import Danmaku from 'danmaku';
// DOM engine only
import Danmaku from 'danmaku/dist/esm/danmaku.dom.js';
// Canvas engine only
import Danmaku from 'danmaku/dist/esm/danmaku.canvas.js';

Usage

Media mode

<div id="my-video-container" style="width:640px;height:360px;position:relative;">
  <video id="my-video" src="./example.mp4" style="position:absolute;"></video>
</div>

<div id="my-audio-container" style="width:640px;height:360px;position:relative;"></div>
<audio id="my-audio" src="./example.mp3"></audio>

<script src="path/to/danmaku.min.js"></script>
<script>
  var danmaku1 = new Danmaku({
    container: document.getElementById('my-video-container'),
    media: document.getElementById('my-video'),
    comments: []
  });
  var danmaku2 = new Danmaku({
    container: document.getElementById('my-audio-container'),
    media: document.getElementById('my-audio'),
    comments: []
  });
</script>

Live mode

To display comments in real time, you need to set up server and use something like Socket.IO. Danmaku is just receiving comments data and display them to container.

Here is a simple example using with Socket.IO and Node.js.

Server:

const app = require('http').createServer(handler);
const io = require('socket.io')(app);
app.listen(80);
function handler(req, res) {
  // your handler...
}
io.on('connection', socket => {
  socket.on('danmaku', comment => {
    socket.broadcast.emit('danmaku', comment);
  });
});

Client:

<div id="my-container" style="width:640px;height:360px;"></div>
<button id="send-button">Send</button>

<script src="path/to/socket.io.js"></script>
<script src="path/to/danmaku.min.js"></script>
<script>
  var danmaku = new Danmaku({
    container: document.getElementById('my-container')
  });
  var socket = io();
  socket.on('danmaku', function(comment) {
    danmaku.emit(comment)
  });
  var btn = document.getElementById('send-button');
  btn.addEventListener('click', function() {
    var comment = {
      text: 'bla bla',
      style: {
        fontSize: '20px',
        color: '#ffffff'
      },
    };
    danmaku.emit(comment);
    socket.emit('danmaku', comment);
  });
</script>

API

Initialization

var danmaku = new Danmaku({
  // REQUIRED. The stage to display comments will be appended to container.
  container: document.getElementById('my-container'),

  // media can be <video> or <audio> element,
  // if it's not provided, Danmaku will be in live mode
  media: document.getElementById('my-media'),

  // Array of comment, used in media mode,
  // you can find its format in `danmaku.emit` API.
  comments: [],

  // You can use DOM engine or canvas engine to render comments.
  // 'DOM' by default in full version.
  engine: 'canvas',

  // You can also set speed by using `danmaku.speed` API.
  speed: 144
});

Emit a comment

danmaku.emit({
  text: 'example',

  // 'rtl'(right to left) by default, available mode: 'ltr', 'rtl', 'top', 'bottom'.
  mode: 'rtl',

  // Specified in seconds, if not provided when using with media,
  // it will be set to `media.currentTime`. Not required in live mode.
  time: 233.3,

  // When using DOM engine, Danmaku will create a <div> node for each comment,
  // the style object will be set to `node.style` directly, just write with CSS rules.
  // For example:
  style: {
    fontSize: '20px',
    color: '#ffffff',
    border: '1px solid #337ab7',
    textShadow: '-1px -1px #000, -1px 1px #000, 1px -1px #000, 1px 1px #000'
  },

  // When using canvas engine, Danmaku will create a <canvas> object for each comment,
  // you should pass in a CanvasRenderingContext2D object.
  // For example:
  style: {
    font: '10px sans-serif',
    textAlign: 'start',
    // Note that 'bottom' is the default
    textBaseline: 'bottom',
    direction: 'inherit',
    fillStyle: '#000',
    strokeStyle: '#000',
    lineWidth: 1.0,
    // ...
  },

  // A custom render to draw comment.
  // when `render` exist, `text` and `style` will be ignored.

  // When using DOM engine, you should return an HTMLElement.
  render: function() {
    var $div = document.createElement('div');
    var $img = document.createElement('img');
    $img.src = '/path/to/xxx.png';
    $div.appendChild($img);
    return $div;
  },
  // When using canvas engine, you should return an HTMLCanvasElement.
  render: function() {
    var canvas = document.createElement('canvas');
    canvas.width = 320;
    canvas.height = 180;
    var ctx = canvas.getContext('2d');
    ctx.beginPath();
    ctx.arc(75, 75, 50, 0, 2 * Math.PI);
    ctx.stroke();
    return canvas;
  }
});

More details about CanvasRenderingContext2D.

Tips:

• With DOM engine, you may want to change line spacing by set line-height to each comment, a better way is set line-height to the container.
• With canvas engine, line height is 1.2 by default, you can set it with style.font.
• With canvas engine, style.font uses the same syntax as the CSS font specifier. However you can only use px, %, em, rem units, I'm sure you don't need others.
• There is a hitbox for each comment, which height is determined by its line height. With canvas engine, when style.textBaseline is top or hanging, the baseline is set to top of the hitbox; when it's middle, baseline is middle of the hitbox; otherwise baseline is bottom of the hitbox. So if you set style.textBaseline to alphabetic or hanging, the comment's head or foot may out of the hitbox and be invisible.
• With canvas engine, style.filter is supported in Chrome 52 and Firefox 49.

Resize

Do it when you resize container.

danmaku.resize();

Show

danmaku.show();

Hide

If you set display: none; to the container directly when using DOM engine, you should also do danmaku.hide() otherwise the typesetting will be broken when it's showed.

danmaku.hide();

Clear

Clear current stage.

danmaku.clear();

Speed

There is a property duration for all comments, which means how long will a comment be shown to the stage. duration is calculated by stage.width / danmaku.speed, and danmaku.speed is a standard for all comments, because the actually speed for each comment is then calculated by (comment.width + stage.width) / duration. The default value is 144.

danmaku.speed = 144;

Destroy

Destroy danmaku instance and release memory.

danmaku.destroy();