libart 2.3.16

[swftools.git] / lib / art / art_alphagamma.c

diff --git a/lib/art/art_alphagamma.c b/lib/art/art_alphagamma.c
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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);
+}