Commit 9ef5947b authored by James Legg's avatar James Legg Committed by Martin Nordholts

Bug 578932 – Alpha weighted blend composting operation

Add new gegl:weighted-blend operation that blends two RGBA buffers
together, using their alpha values as weights.
parent a17972ee
/* 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)
{
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)
{
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<n_pixels; i++)
{
gint j;
gfloat c;
gfloat value;
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;
operation_class->name = "gegl:weighted-blend";
operation_class->categories = "compositors:blend";
operation_class->description =
_("blend two images using alpha values as weights");
}
#endif
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