Declus - GIF manipulation

Playing with GIF images made much easier

Installation & Usage

npm i declus

const declus = require('declus');

// Using callback
declus(options)
  .then((buffer) => {
    ...
  })
  .catch(console.error);

// Inside an async function, using await
const buffer = await declus(options);

| :warning: Requires access to write extracted frames to a directory. If file-system is restricted, use the inMemory option to store extracted frames in memory | | --- |

Getting started

Basic example

const fs = require('fs');
const declus = require('declus');

declus({
  height: 360,
  width: 640,
  baseLayer: {
    data: 'https://raw.githubusercontent.com/HexM7/declus/master/assets/sample.gif',
  },
  layers: [
    {
      data: 'https://raw.githubusercontent.com/HexM7/declus/master/assets/transparentKitten.png',
    }
  ],
  stretchLayers: true,
}).then((buffer) => {
  fs.createWriteStream('./myImage.gif')
    .write(buffer);
});

Accepts Buffer, absolute URLs and paths to images

data: myBuffer,
data: './sampleImage.gif',

Layer options

layer: {
  data: Buffer || URL || Path, // Required
  marginLeft: Number,
  marginTop: Number,
  width: Number,
  height: Number,
  drawFunction: function(context, layerImg, index, totalFrames),
  skipFunction: function(index, totalFrames),
  skipIndexes: Array,
}

• data - Layer data, can be an image buffer, URL or path.
• marginLeft - Left layer margin relative to the base width.
• marginTop - Top layer margin relative to the base height.
• width - Layer width.
• height - Layer height.
• drawFunction - A custom function to draw the layer onto the base layer.

{
  drawFunction: function(context, layerImg, index, totalFrames) {
    const drawProgress = (index / totalFrames).toFixed(1);

    context.drawImage(
      layerImg,
      width * drawProgress,
      height * drawProgress,
      64,
      64,
    );
  },
}

• skipFunction - Function to decide wether or not to skip the current frame. Return true to skip and false to render the frame.

{
  skipFunction: function(index, totalFrames) {
    // Skip all frames with even index
    if (index % 2 === 0) return true;
    return false;
  },
}

• skipIndexes - Frames indexes to skip layers.

{
  skipIndexes: [5, 15, 25, 50],
}

Options

*width number

Width of the output image.

*height number

Height of the output image.

*baseLayer object

An object with data to build the base layer.

Check baseLayer options.

layers array

An array of layer objects. The stacking order is defined by the position of the layer in the array.

Check layer options.

repeat number

Amount of times to repeat the output GIF.

• -1: play once
• 0: default, loop indefinitely
• Positive number: loop specific times

quality number

The quality of output GIF (computational/performance trade-off).

• 1: best colors, worst performance
• 20: suggested maximum but there is no limit
• 10: default, provided an even trade-off

delay number, ms

Amount of milliseconds to delay between frames.

frameRate number

Frames per second.

| :warning: delay and frameRate cannot be used together | | --- |

alpha boolean

Wether or not to have a transparent background.

alphaColor number, hexadecimal

Defines the color which represents transparency in the output GIF.

coalesce boolean

Whether or not to perform inter-frame coalescing, defaults to true.

stretchLayers boolean

Whether or not to stretch the layers to their maximum, defaults to false.

encoderOptions object

Options passed to gif-encoder.

• highWaterMark: Number, in bytes, to store in internal buffer. Defaults to 64kB. Increase if you face GIF memory limit exceeded error.

outputDir string

Directory to store temporary frames extracted from the GIF, defaults to . (root). A new folder is created and automatically gets removed after the encoding has been finished.

inMemory boolean

Whether or not to extract frames to memory store instead of writing them to a directory. If true, the GIF image will render faster as the frames will be written and read from the memory instead of a directory at cost of increasing memory usage such as when dealing with large images. Useful when you do not have access to write to the file system. Defaults to false.

frameExtension string

Extension of the extracted frames from the GIF, defaults to png.

Allowed formats:

• png
• jpg
• gif(static)

outputFilename string

Filename for the output GIF image. Defaults to a unique ID generated through nanoid.

Events

initCanvasContext function(context)

A function called during the initialization of the Canvas context.

beforeBaseLayerDraw function(context, layerImg, index, totalFrames)

A function called each time before a frame of the base layer is drawn.

afterBaseLayerDraw function(context, layerImg, index, totalFrames)

A function called each time after a frame of the base layer is drawn.

beforeLayerDraw function(context, layerImg, index, totalFrames, layerIndex)

A function called each time before a frame of a layer is drawn.

afterLayerDraw function(context, layerImg, index, totalFrames, layerIndex)

A function called each time after a frame of a layer is drawn.

encoderOnData function(buffer)

Emits a Buffer containing either header bytes, frame bytes, or footer bytes.

encoderOnEnd function

Signifies end of the encoding has been reached.

encoderOnError function(error)

Emits an Error when internal buffer is exceeded.

encoderOnReadable function

Emits when the stream is ready to be .read() from.

encoderOnWriteHeader function

Emits when at the start and end of .writeHeader().

encoderOnFrame function

Emits when a new frame is being rendered.

encoderOnFinish function

Emits when encoding has been finished.

Credits

• @transitive-bullshit for gif-extract-frames