/* 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;

}