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86 lines
2.6 KiB
C
86 lines
2.6 KiB
C
/* Libart_LGPL - library of basic graphic primitives
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* Copyright (C) 1998 Raph Levien
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Library General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Library General Public License for more details.
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*
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* You should have received a copy of the GNU Library General Public
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* License along with this library; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 02111-1307, USA.
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*/
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/* Some functions to build alphagamma tables */
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#include <math.h>
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#include "art_misc.h"
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#include "art_alphagamma.h"
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/**
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* art_alphagamma_new: Create a new #ArtAlphaGamma.
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* @gamma: Gamma value.
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*
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* Create a new #ArtAlphaGamma for a specific value of @gamma. When
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* correctly implemented (which is generally not the case in libart),
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* alpha compositing with an alphagamma parameter is equivalent to
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* applying the gamma transformation to source images, doing the alpha
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* compositing (in linear intensity space), then applying the inverse
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* gamma transformation, bringing it back to a gamma-adjusted
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* intensity space.
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*
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* Return value: The newly created #ArtAlphaGamma.
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**/
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ArtAlphaGamma *
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art_alphagamma_new (double gamma)
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{
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int tablesize;
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ArtAlphaGamma *alphagamma;
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int i;
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int *table;
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art_u8 *invtable;
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double s, r_gamma;
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tablesize = ceil (gamma * 8);
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if (tablesize < 10)
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tablesize = 10;
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alphagamma = (ArtAlphaGamma *)art_alloc (sizeof(ArtAlphaGamma) +
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((1 << tablesize) - 1) *
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sizeof(art_u8));
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alphagamma->gamma = gamma;
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alphagamma->invtable_size = tablesize;
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table = alphagamma->table;
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for (i = 0; i < 256; i++)
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table[i] = (int)floor (((1 << tablesize) - 1) *
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pow (i * (1.0 / 255), gamma) + 0.5);
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invtable = alphagamma->invtable;
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s = 1.0 / ((1 << tablesize) - 1);
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r_gamma = 1.0 / gamma;
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for (i = 0; i < 1 << tablesize; i++)
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invtable[i] = (int)floor (255 * pow (i * s, r_gamma) + 0.5);
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return alphagamma;
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}
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/**
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* art_alphagamma_free: Free an #ArtAlphaGamma.
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* @alphagamma: An #ArtAlphaGamma.
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*
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* Frees the #ArtAlphaGamma.
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**/
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void
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art_alphagamma_free (ArtAlphaGamma *alphagamma)
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{
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art_free (alphagamma);
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}
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