/**
 * Sepia Filter
 * Based on: Pixastic Lib - Sepia filter - v0.1.0
 * Copyright (c) 2008 Jacob Seidelin, jseidelin@nihilogic.dk, http://blog.nihilogic.dk/
 * @function
 * @name Sepia
 * @memberof Konva.Filters
 * @param {Object} imageData
 * @author Jacob Seidelin <jseidelin@nihilogic.dk>
 * @license MPL v1.1 [http://www.pixastic.com/lib/license.txt]
 * @example
 * node.cache();
 * node.filters([Konva.Filters.Sepia]);
 */

export const Sepia = function(imageData) {
  var data = imageData.data,
    w = imageData.width,
    y = imageData.height,
    w4 = w * 4,
    offsetY,
    x,
    offset,
    or,
    og,
    ob,
    r,
    g,
    b;

  do {
    offsetY = (y - 1) * w4;
    x = w;
    do {
      offset = offsetY + (x - 1) * 4;

      or = data[offset];
      og = data[offset + 1];
      ob = data[offset + 2];

      r = or * 0.393 + og * 0.769 + ob * 0.189;
      g = or * 0.349 + og * 0.686 + ob * 0.168;
      b = or * 0.272 + og * 0.534 + ob * 0.131;

      data[offset] = r > 255 ? 255 : r;
      data[offset + 1] = g > 255 ? 255 : g;
      data[offset + 2] = b > 255 ? 255 : b;
      data[offset + 3] = data[offset + 3];
    } while (--x);
  } while (--y);
};