index.js

import { isNodePattern, throwError } from '@jimp/utils';

/**
 * Displaces the image based on the provided displacement map
 * @param {object} map the source Jimp instance
 * @param {number} offset the maximum displacement value
 * @param {function(Error, Jimp)} cb (optional) a callback for when complete
 * @returns {Jimp} this for chaining of methods
 */
export default () => ({
  displace(map, offset, cb) {
    if (typeof map !== 'object' || map.constructor !== this.constructor) {
      return throwError.call(this, 'The source must be a Jimp image', cb);
    }

    if (typeof offset !== 'number') {
      return throwError.call(this, 'factor must be a number', cb);
    }

    const source = this.cloneQuiet();
    this.scanQuiet(0, 0, this.bitmap.width, this.bitmap.height, function(
      x,
      y,
      idx
    ) {
      let displacement = (map.bitmap.data[idx] / 256) * offset;
      displacement = Math.round(displacement);

      const ids = this.getPixelIndex(x + displacement, y);
      this.bitmap.data[ids] = source.bitmap.data[idx];
      this.bitmap.data[ids + 1] = source.bitmap.data[idx + 1];
      this.bitmap.data[ids + 2] = source.bitmap.data[idx + 2];
    });

    if (isNodePattern(cb)) {
      cb.call(this, null, this);
    }

    return this;
  }
});