/* dzl-rgba.c
 *
 * Copyright (C) 2014 Christian Hergert <christian@hergert.me>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#define G_LOG_DOMAIN "dzl-rgba"

#include "config.h"

#include "dzl-rgba.h"

/*
 * The following code is borrowed ultimately upstream through Clearlooks
 * theme engine in 2.x days. It has been ported to use GdkRGBA. It exists
 * all over the place, feel free to use this under any license compatible
 * with upstream.
 */

/* Clearlooks - a cairo based GTK+ engine
 * Copyright (C) 2006 Andrew Johnson <acjgenius@earthlink.net>
 * Copyright (C) 2007 Benjamin Berg <benjamin@sipsolutions.net>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */


static void
rgb_to_hls (gdouble *r,
            gdouble *g,
            gdouble *b)
{
  gdouble min;
  gdouble max;
  gdouble red;
  gdouble green;
  gdouble blue;
  gdouble h, l, s;
  gdouble delta;

  red = *r;
  green = *g;
  blue = *b;
  if (red > green)
    {
      if (red > blue)
        max = red;
      else
        max = blue;
      if (green < blue)
        min = green;
      else
        min = blue;
    }
  else
    {
      if (green > blue)
        max = green;
      else
        max = blue;
      if (red < blue)
        min = red;
      else
        min = blue;
    }
  l = (max + min) / 2;
  s = 0;
  h = 0;
  if (max != min)
    {
      if (l <= 0.5)
        s = (max - min) / (max + min);
      else
        s = (max - min) / (2 - max - min);
      delta = max - min;
      if (red == max)
        h = (green - blue) / delta;
      else if (green == max)
        h = 2 + (blue - red) / delta;
      else if (blue == max)
        h = 4 + (red - green) / delta;
      h *= 60;
      if (h < 0.0)
        h += 360;
    }
  *r = h;
  *g = l;
  *b = s;
}

static void
hls_to_rgb (gdouble *h,
            gdouble *l,
            gdouble *s)
{
  gdouble hue;
  gdouble lightness;
  gdouble saturation;
  gdouble m1, m2;
  gdouble r, g, b;

  lightness = *l;
  saturation = *s;
  if (lightness <= 0.5)
    m2 = lightness * (1 + saturation);
  else
    m2 = lightness + saturation - lightness * saturation;
  m1 = 2 * lightness - m2;
  if (saturation == 0)
    {
      *h = lightness;
      *l = lightness;
      *s = lightness;
    }
  else
    {
      hue = *h + 120;
      while (hue > 360)
        hue -= 360;
      while (hue < 0)
        hue += 360;
      if (hue < 60)
        r = m1 + (m2 - m1) * hue / 60;
      else if (hue < 180)
        r = m2;
      else if (hue < 240)
        r = m1 + (m2 - m1) * (240 - hue) / 60;
      else
        r = m1;
      hue = *h;
      while (hue > 360)
        hue -= 360;
      while (hue < 0)
        hue += 360;
      if (hue < 60)
        g = m1 + (m2 - m1) * hue / 60;
      else if (hue < 180)
        g = m2;
      else if (hue < 240)
        g = m1 + (m2 - m1) * (240 - hue) / 60;
      else
        g = m1;
      hue = *h - 120;
      while (hue > 360)
        hue -= 360;
      while (hue < 0)
        hue += 360;
      if (hue < 60)
        b = m1 + (m2 - m1) * hue / 60;
      else if (hue < 180)
        b = m2;
      else if (hue < 240)
        b = m1 + (m2 - m1) * (240 - hue) / 60;
      else
        b = m1;
      *h = r;
      *l = g;
      *s = b;
    }
}

void
dzl_rgba_shade (const GdkRGBA *rgba,
                GdkRGBA       *dst,
                gdouble        k)
{
  gdouble red;
  gdouble green;
  gdouble blue;

  red = rgba->red;
  green = rgba->green;
  blue = rgba->blue;

  rgb_to_hls (&red, &green, &blue);

  green *= k;

  if (green > 1.0)
    green = 1.0;
  else if (green < 0.0)
    green = 0.0;

  blue *= k;

  if (blue > 1.0)
    blue = 1.0;
  else if (blue < 0.0)
    blue = 0.0;

  hls_to_rgb (&red, &green, &blue);

  dst->red = red;
  dst->green = green;
  dst->blue = blue;
  dst->alpha = rgba->alpha;
}