Dissolve blending mode

[Ville Sokk <ville.sokk@xxxxxxxxx>]

Dissolve blending mode. The category should be changed, I don't know
about the compositor categories so I just left it at
"compositors:math". I tried to follow the way GIMP's dissolve works
but gegl is obviously different. There's no mask or opacity input like
in GIMP, I assume masking or gegl:opacity is already done on the
inputs. Tell me if I need to change something or add those properties.

#include "config.h"
#include <glib/gi18n-lib.h>

#ifdef GEGL_CHANT_PROPERTIES
/* no properties */
#else

#define GEGL_CHANT_TYPE_COMPOSER
#define GEGL_CHANT_C_FILE       "dissolve.c"

#include "gegl-chant.h"


#define RANDOM_TABLE_SIZE    4096
static gint32  random_table[RANDOM_TABLE_SIZE];

static void prepare (GeglOperation *operation)
{
  Babl  *format = babl_format ("RGBA float");
  GRand *gr;
  gint   i;

#define RANDOM_SEED 314159265

  gegl_operation_set_format (operation, "input", format);
  gegl_operation_set_format (operation, "aux", format);
  gegl_operation_set_format (operation, "output", format);

  /* generate a table of random seeds */
  gr = g_rand_new_with_seed (RANDOM_SEED);
  for (i = 0; i < RANDOM_TABLE_SIZE; i++)
    {
      random_table[i] = g_rand_int (gr);
    }

  g_rand_free (gr);
}

static GeglRectangle
get_required_for_output (GeglOperation *operation,
                         const gchar *input_pad,
                         const GeglRectangle *region)
{
  GeglRectangle result = *gegl_operation_source_get_bounding_box (operation, "input");

  return result;
}

static gboolean
process (GeglOperation       *operation,
         GeglBuffer          *input,
         GeglBuffer          *aux,
         GeglBuffer          *output,
         const GeglRectangle *result)
{
  GeglBufferIterator *it;
  GRand              *gr;
  Babl               *format;
  gint                index_in, index_out, index_aux;

  if (aux == NULL)
    {
      gegl_buffer_copy (input, result, output, result);

      return TRUE;
    }

  format = babl_format ("RGBA float");
  it = gegl_buffer_iterator_new (output, result, format, GEGL_BUFFER_WRITE);
  index_out = 0;
  index_in = gegl_buffer_iterator_add (it, input, result, format, GEGL_BUFFER_READ);
  index_aux = gegl_buffer_iterator_add (it, aux, result, format, GEGL_BUFFER_READ);

  while (gegl_buffer_iterator_next (it))
    {
      gint    row, pix, i;
      gdouble rand_val;
      gint    x = it->roi->x;
      gint    y = it->roi->y;
      gint    width = it->roi->width;
      gint    height = it->roi->height;
      gfloat *in = it->data[index_in];
      gfloat *out = it->data[index_out];
      gfloat *aux = it->data[index_aux];

      for (row = 0; row < height; row++)
        {
          gr = g_rand_new_with_seed (random_table[(y + row) % RANDOM_TABLE_SIZE]);
          for (i = 0; i < x; i++)
            {
              g_rand_int (gr);
            }

          for (pix = 0; pix < width; pix++)
            {
              /* dissolve if random value is >= opacity */
              rand_val = g_rand_double_range (gr, 0., 1.);

              /* colour channels */
              for (i = 0; i < 3; i++)
                {
                  out[i] = rand_val >= aux[3] ? in[i] : aux[i];
                }

              /* alpha channel */
              out[3] = rand_val >= aux[3] ? 1. : in[3];

              in += 4;
              aux += 4;
              out+= 4;
            }
        }
    }

  g_rand_free (gr);

  return TRUE;
}

static void
gegl_chant_class_init (GeglChantClass *klass)
{
  GeglOperationClass         *operation_class;
  GeglOperationComposerClass *composer_class;

  operation_class  = GEGL_OPERATION_CLASS (klass);
  composer_class   = GEGL_OPERATION_COMPOSER_CLASS (klass);

  composer_class->process = process;
  operation_class->prepare = prepare;
  operation_class->get_required_for_output = get_required_for_output;

  operation_class->name        = "gegl:dissolve";
  operation_class->categories  = "compositors:math";
  operation_class->description = _("Dissolve blend operation");
}
#endif

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