[gegl] workshop: add lowbit-dither, experimental dithering for floating point

[Øyvind Kolås <ok src gnome org>]

commit 9babb32603c1adbc8103d847af3d605e2d197ed8
Author: Øyvind Kolås <pippin gimp org>
Date:   Tue Dec 20 23:04:41 2016 +0100

    workshop: add lowbit-dither, experimental dithering for floating point

 operations/workshop/Makefile.am     |    1 +
 operations/workshop/lowbit-dither.c |  105 +++++++++++++++++++++++++++++++++++
 2 files changed, 106 insertions(+), 0 deletions(-)
---
diff --git a/operations/workshop/Makefile.am b/operations/workshop/Makefile.am
index 93e7686..13f3949 100644
--- a/operations/workshop/Makefile.am
+++ b/operations/workshop/Makefile.am
@@ -25,6 +25,7 @@ op_LTLIBRARIES =    \
        rawbayer-load.la \
        unpremul.la \
     vhsfix.la \
+    lowbit-dither.la \
     waterpixels.la \
     watershed-transform.la \
     wavelet-blur.la
diff --git a/operations/workshop/lowbit-dither.c b/operations/workshop/lowbit-dither.c
new file mode 100644
index 0000000..ac9cb7a
--- /dev/null
+++ b/operations/workshop/lowbit-dither.c
@@ -0,0 +1,105 @@
+/* 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 2016 Øyvind Kolås <pippin gimp org>
+ */
+
+#include "config.h"
+#include <glib/gi18n-lib.h>
+
+#ifdef GEGL_PROPERTIES
+
+#else
+
+#define GEGL_OP_POINT_FILTER
+#define GEGL_OP_C_SOURCE lowbit-dither.c
+#define GEGL_OP_NAME     lowbit_dither
+
+#include "gegl-op.h"
+
+#include <math.h>
+
+static void
+prepare (GeglOperation *operation)
+{
+  gegl_operation_set_format (operation, "input", babl_format ("R'G'B'A float"));
+  gegl_operation_set_format (operation, "output", babl_format ("R'G'B'A float"));
+}
+
+static gboolean
+process (GeglOperation       *operation,
+         void                *in_buf,
+         void                *out_buf,
+         glong                n_pixels,
+         const GeglRectangle *roi,
+         gint                 level)
+{
+  //GeglProperties *o = GEGL_PROPERTIES (operation);
+  gfloat     *in_pixel =  in_buf;
+  gfloat     *out_pixel = out_buf;
+  gint        x, y;
+
+  x = roi->x;
+  y = roi->y;
+
+  while (n_pixels--)
+    {
+      int ch;
+      for (ch = 0; ch < 4; ch++)
+      {
+       if (in_pixel [ch] > 0.0000001f && in_pixel [ch] < 1.0000000f)
+         out_pixel [ch] = in_pixel [ch] + ((((((x+ch * 67) + y * 236) * 119) & 255)/255.0f)-0.5f )/255.0f;
+         /* this computes an 8bit http://pippin.gimp.org/a_dither/ mask */
+       else
+         out_pixel [ch] = in_pixel [ch];
+      }
+      out_pixel += 4;
+      in_pixel  += 4;
+
+      /* update x and y coordinates */
+      if (++x>=roi->x + roi->width)
+        {
+          x=roi->x;
+          y++;
+        }
+    }
+
+  return  TRUE;
+}
+
+static void
+gegl_op_class_init (GeglOpClass *klass)
+{
+  GeglOperationClass            *operation_class;
+  GeglOperationPointFilterClass *point_filter_class;
+
+  operation_class    = GEGL_OPERATION_CLASS (klass);
+  point_filter_class = GEGL_OPERATION_POINT_FILTER_CLASS (klass);
+
+  operation_class->prepare        = prepare;
+  operation_class->no_cache       = TRUE;
+  operation_class->opencl_support = TRUE;
+
+  point_filter_class->process    = process;
+
+  gegl_operation_class_set_keys (operation_class,
+    "name",               "gegl:lowbit-dither",
+    "title",              _("Lowbit dither"),
+    "position-dependent", "true",
+    "description", _("dithers adequately to mask out 8bit sRGB TRC quantization for high bitdepth formats"),
+    NULL);
+}
+
+#endif