index.js

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

/**
 * Scale the image to the given width and height keeping the aspect ratio. Some parts of the image may be letter boxed.
 * @param {number} w the width to resize the image to
 * @param {number} h the height to resize the image to
 * @param {number} alignBits (optional) A bitmask for horizontal and vertical alignment
 * @param {string} mode (optional) a scaling method (e.g. Jimp.RESIZE_BEZIER)
 * @param {function(Error, Jimp)} cb (optional) a callback for when complete
 * @returns {Jimp} this for chaining of methods
 */
export default () => ({
  contain(w, h, alignBits, mode, cb) {
    if (typeof w !== 'number' || typeof h !== 'number') {
      return throwError.call(this, 'w and h must be numbers', cb);
    }

    // permit any sort of optional parameters combination
    if (typeof alignBits === 'string') {
      if (typeof mode === 'function' && typeof cb === 'undefined') cb = mode;
      mode = alignBits;
      alignBits = null;
    }

    if (typeof alignBits === 'function') {
      if (typeof cb === 'undefined') cb = alignBits;
      mode = null;
      alignBits = null;
    }

    if (typeof mode === 'function' && typeof cb === 'undefined') {
      cb = mode;
      mode = null;
    }

    alignBits =
      alignBits ||
      this.constructor.HORIZONTAL_ALIGN_CENTER |
        this.constructor.VERTICAL_ALIGN_MIDDLE;
    const hbits = alignBits & ((1 << 3) - 1);
    const vbits = alignBits >> 3;

    // check if more flags than one is in the bit sets
    if (
      !(
        (hbits !== 0 && !(hbits & (hbits - 1))) ||
        (vbits !== 0 && !(vbits & (vbits - 1)))
      )
    ) {
      return throwError.call(
        this,
        'only use one flag per alignment direction',
        cb
      );
    }

    const alignH = hbits >> 1; // 0, 1, 2
    const alignV = vbits >> 1; // 0, 1, 2

    const f =
      w / h > this.bitmap.width / this.bitmap.height
        ? h / this.bitmap.height
        : w / this.bitmap.width;
    const c = this.cloneQuiet().scale(f, mode);

    this.resize(w, h, mode);
    this.scanQuiet(0, 0, this.bitmap.width, this.bitmap.height, function(
      x,
      y,
      idx
    ) {
      this.bitmap.data.writeUInt32BE(this._background, idx);
    });
    this.blit(
      c,
      ((this.bitmap.width - c.bitmap.width) / 2) * alignH,
      ((this.bitmap.height - c.bitmap.height) / 2) * alignV
    );

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

    return this;
  }
});