[gegl] Added an op that can be used to fix a wrongly premultiplied buffer.

[Øyvind Kolås <ok src gnome org>]

commit 93534cb3227f66d041290076310492ea8dbc8790
Author: �yvind Kolås <pippin gimp org>
Date:   Tue Nov 10 02:27:11 2009 +0000

    Added an op that can be used to fix a wrongly premultiplied buffer.
    
    This is a hack, that probably shall remain in the workshop.

 operations/workshop/unpremul.c |   76 ++++++++++++++++++++++++++++++++++++++++
 1 files changed, 76 insertions(+), 0 deletions(-)
---
diff --git a/operations/workshop/unpremul.c b/operations/workshop/unpremul.c
new file mode 100644
index 0000000..6d6883b
--- /dev/null
+++ b/operations/workshop/unpremul.c
@@ -0,0 +1,76 @@
+/* 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 �yvind Kolås <pippin gimp org>
+ */
+
+#ifdef GEGL_CHANT_PROPERTIES
+
+   /* no properties */
+
+#else
+
+#define GEGL_CHANT_TYPE_POINT_FILTER
+#define GEGL_CHANT_C_FILE       "unpremul.c"
+#define GEGLV4
+
+#include "gegl-chant.h"
+
+static gboolean
+process (GeglOperation       *op,
+         void                *in_buf,
+         void                *out_buf,
+         glong                samples,
+         const GeglRectangle *roi)
+{
+  glong   i;
+  gfloat *in  = in_buf;
+  gfloat *out = out_buf;
+
+  for (i=0; i<samples; i++)
+    {
+      int  j;
+      for (j=0; j<3; j++)
+        {
+          if (in[3] != 0)
+            out[j] = in[j] / in[3];
+          else
+            out[j] = 0.0;
+        }
+      out[3]=in[3];
+      in += 4;
+      out+= 4;
+    }
+  return TRUE;
+}
+
+
+static void
+gegl_chant_class_init (GeglChantClass *klass)
+{
+  GeglOperationClass            *operation_class;
+  GeglOperationPointFilterClass *point_filter_class;
+
+  operation_class    = GEGL_OPERATION_CLASS (klass);
+  point_filter_class = GEGL_OPERATION_POINT_FILTER_CLASS (klass);
+
+  point_filter_class->process = process;
+
+  operation_class->name        = "gegl:unpremul";
+  operation_class->categories  = "color";
+  operation_class->description = "Unpremultiplies a buffer that contains pre-multiplied colors (but is marked as not having it)";
+}
+
+#endif