/* This file is an image processing operation for GEGL

 *

 * GEGL 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 3 of the License, or (at your option) any later version.

 *

 * GEGL 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 GEGL; if not, see <http://www.gnu.org/licenses/>.

 *

 * Copyright 2006 Øyvind Kolås <pippin@gimp.org>

 *           2008 James Legg

 */

#include "config.h"

#include <glib/gi18n-lib.h>

#ifdef GEGL_CHANT_PROPERTIES

gegl_chant_double (value, _("Value"), -G_MAXDOUBLE, G_MAXDOUBLE, 0.0, _("global value used if aux doesn't contain data"))

#else

#define GEGL_CHANT_TYPE_POINT_COMPOSER

#define GEGL_CHANT_C_FILE       "weighted-blend.c"

#include "gegl-chant.h"

static void prepare (GeglOperation *operation)

{

  const Babl *format = babl_format ("RGBA float");

  gegl_operation_set_format (operation, "input", format);

  gegl_operation_set_format (operation, "aux", format);

  gegl_operation_set_format (operation, "output", format);

}

static gboolean

process (GeglOperation       *op,

         void                *in_buf,

         void                *aux_buf,

         void                *out_buf,

         glong                n_pixels,

         const GeglRectangle *roi,

         gint                 level)

{

  gfloat *in  = in_buf;

  gfloat *out = out_buf;

  gfloat *aux = aux_buf;

  gint    i;

  if (aux == NULL)

    {

      /* there is no auxilary buffer.

       * output the input buffer.

       * gfloat value = GEGL_CHANT_PROPERTIES (op)->value;

       */

      for (i = 0; i < n_pixels; i++)

        {

          gint j;

          for (j = 0; j < 4; j++)

            {

              out[j] = in[j];

            }

        }

    }

  else

    {

      for (i=0; i

        {

          gint   j;

          gfloat total_alpha;

          /* find the proportion between alpha values */

          total_alpha = in[3] + aux[3];

          if (!total_alpha)

            {

              /* no coverage from any source pixel */

              for (j = 0; j < 4; j++)

                {

                  out[j] = 0.0;

                }

            }

          else

            {

              /* the total alpha is non-zero, therefore we may find a colour from a weighted blend */

              gfloat in_weight = in[3] / total_alpha;

              gfloat aux_weight = 1.0 - in_weight;

              for (j = 0; j < 3; j++)

                {

                  out[j] = in_weight * in[j] + aux_weight * aux[j];

                }

              out[3] = total_alpha;

            }

          in  += 4;

          aux += 4;

          out += 4;

        }

    }

  return TRUE;

}

static void

gegl_chant_class_init (GeglChantClass *klass)

{

  GeglOperationClass              *operation_class;

  GeglOperationPointComposerClass *point_composer_class;

  operation_class      = GEGL_OPERATION_CLASS (klass);

  point_composer_class = GEGL_OPERATION_POINT_COMPOSER_CLASS (klass);

  point_composer_class->process = process;

  operation_class->prepare      = prepare;

  gegl_operation_class_set_keys (operation_class,

    "name"       , "gegl:weighted-blend",

    "categories" , "compositors:blend",

    "description",

      _("blend two images using alpha values as weights"),

    NULL);

}

#endif