distort.js

/**
 * This module provides a function `distortImage` that takes a URL of an image and distorts it.
 * Returns a promise containing a buffer.
 *
 * For dependencies, you need
 * 1. The ImageMagick binary (https://www.imagemagick.org/script/download.php)
 * 2. The GraphicsMagick JS library (https://github.com/aheckmann/gm)
 *    - `npm i gm`
 * 3. The Jimp library (https://github.com/oliver-moran/jimp)
 *    - `npm i jimp`
 **/

const im = require('gm').subClass({
    imageMagick: true
});
const Jimp = require('jimp');

function distortImage(url) {
    return new Promise((resolve, reject) => {
        Jimp.read(url).then(img1 => { // Use Jimp to read from a url
            if (img1.bitmap.width == 400 && img1.bitmap.height == 620) // Verify the correct dimensions before cropping
                img1.crop(27, 69, 344, 410); // Crop the card contents
            const filters = [
                { apply: getRandomInt(0, 1) == 1 ? 'desaturate' : 'saturate', params: [getRandomInt(40, 80)] },
                { apply: 'spin', params: [getRandomInt(10, 350)] }
            ];
            img1.color(filters); // Do some recolouring

            img1.getBuffer(Jimp.MIME_PNG, (err, buffer) => {
                if (err) {
                    reject(err); return;
                }
                let img2 = im(buffer); // Read into ImageMagick for manipulation
                let horizRoll = getRandomInt(0, img1.bitmap.width),
                    vertiRoll = getRandomInt(0, img1.bitmap.height);
                img2.out('-implode').out(`-${getRandomInt(3, 10)}`);
                img2.out('-roll').out(`+${horizRoll}+${vertiRoll}`);
                img2.out('-swirl').out(`${getRandomInt(0, 1) == 1 ? '+' : '-'}${getRandomInt(120, 180)}`);

                img2.setFormat('png').toBuffer(function (err, buffer) { // Export as buffer. We're done.
                    if (err) {
                        reject(err); return;
                    }
                    resolve(buffer);
                });
            });
        });
    });
}

function getRandomInt(min, max) { // generic random number generator
    return Math.floor(Math.random() * (max - min + 1)) + min;
};

module.exports = distortImage;