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/* Libart_LGPL - library of basic graphic primitives
* Copyright (C) 1998 Raph Levien
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 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
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
/* Some functions to build alphagamma tables */
#include "config.h"
#include "art_alphagamma.h"
#include <math.h>
/**
* art_alphagamma_new: Create a new #ArtAlphaGamma.
* @gamma: Gamma value.
*
* Create a new #ArtAlphaGamma for a specific value of @gamma. When
* correctly implemented (which is generally not the case in libart),
* alpha compositing with an alphagamma parameter is equivalent to
* applying the gamma transformation to source images, doing the alpha
* compositing (in linear intensity space), then applying the inverse
* gamma transformation, bringing it back to a gamma-adjusted
* intensity space.
*
* Return value: The newly created #ArtAlphaGamma.
**/
ArtAlphaGamma *
art_alphagamma_new (double gamma)
{
int tablesize;
ArtAlphaGamma *alphagamma;
int i;
int *table;
art_u8 *invtable;
double s, r_gamma;
tablesize = ceil (gamma * 8);
if (tablesize < 10)
tablesize = 10;
alphagamma = (ArtAlphaGamma *)art_alloc (sizeof(ArtAlphaGamma) +
((1 << tablesize) - 1) *
sizeof(art_u8));
alphagamma->gamma = gamma;
alphagamma->invtable_size = tablesize;
table = alphagamma->table;
for (i = 0; i < 256; i++)
table[i] = (int)floor (((1 << tablesize) - 1) *
pow (i * (1.0 / 255), gamma) + 0.5);
invtable = alphagamma->invtable;
s = 1.0 / ((1 << tablesize) - 1);
r_gamma = 1.0 / gamma;
for (i = 0; i < 1 << tablesize; i++)
invtable[i] = (int)floor (255 * pow (i * s, r_gamma) + 0.5);
return alphagamma;
}
/**
* art_alphagamma_free: Free an #ArtAlphaGamma.
* @alphagamma: An #ArtAlphaGamma.
*
* Frees the #ArtAlphaGamma.
**/
void
art_alphagamma_free (ArtAlphaGamma *alphagamma)
{
art_free (alphagamma);
}
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