[gegl] Add an implementation of Darktable's exposure filter

[Debarshi Ray <debarshir src gnome org>]

commit f7367bf8c68493e05bcb8592e4d495dcc0f11534
Author: Debarshi Ray <debarshir gnome org>
Date:   Thu Feb 2 15:54:19 2017 +0100

    Add an implementation of Darktable's exposure filter
    
    It doesn't support all the different parameters that Darktable does,
    but just the exposure and black adjustment.

 operations/workshop/Makefile.am   |    1 +
 operations/workshop/dt-exposure.c |  108 +++++++++++++++++++++++++++++++++++++
 po/POTFILES.in                    |    1 +
 3 files changed, 110 insertions(+), 0 deletions(-)
---
diff --git a/operations/workshop/Makefile.am b/operations/workshop/Makefile.am
index d5afe1a..cd45023 100644
--- a/operations/workshop/Makefile.am
+++ b/operations/workshop/Makefile.am
@@ -16,6 +16,7 @@ op_LTLIBRARIES =    \
        demosaic-bimedian.la \
        demosaic-simple.la \
        ditto.la \
+       dt-exposure.la \
        gradient-map.la \
        hstack.la \
        integral-image.la \
diff --git a/operations/workshop/dt-exposure.c b/operations/workshop/dt-exposure.c
new file mode 100644
index 0000000..de7d93f
--- /dev/null
+++ b/operations/workshop/dt-exposure.c
@@ -0,0 +1,108 @@
+/* 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 2017 Red Hat, Inc.
+ */
+
+#include "config.h"
+#include <glib/gi18n-lib.h>
+
+#ifdef GEGL_PROPERTIES
+
+property_double (black, _("Black"), 0.0)
+    description (_("Adjust the black level"))
+    value_range (-0.1, 0.1)
+
+property_double (exposure, _("Exposure"), 0.0)
+    description (_("Adjust the exposure correction"))
+    value_range (-3.0, 3.0)
+
+#else
+
+#define GEGL_OP_POINT_FILTER
+#define GEGL_OP_NAME     dt_exposure
+#define GEGL_OP_C_SOURCE dt-exposure.c
+
+#include "gegl-op.h"
+
+#include <math.h>
+
+static void
+prepare (GeglOperation *operation)
+{
+  const Babl *format;
+
+  format = babl_format ("R'G'B'A float");
+  gegl_operation_set_format (operation, "input", format);
+  gegl_operation_set_format (operation, "output", format);
+}
+
+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 = in_buf;
+  gfloat *out = out_buf;
+  gfloat black = (gfloat) o->black;
+  gfloat diff;
+  gfloat exposure_negated = (gfloat) -o->exposure;
+  gfloat scale;
+  gfloat white;
+  glong i;
+
+  white = exp2f (exposure_negated);
+  diff = MAX (white - black, 0.01);
+  scale = 1.0f / diff;
+
+  for (i = 0; i < n_pixels; i++)
+    {
+      out[0] = (in[0] - black) * scale;
+      out[1] = (in[1] - black) * scale;
+      out[2] = (in[2] - black) * scale;
+      out[3] = in[3];
+
+      in += 4;
+      out += 4;
+    }
+
+  return TRUE;
+}
+
+static void
+gegl_op_class_init (GeglOpClass *klass)
+{
+  GeglOperationClass *operation_class = GEGL_OPERATION_CLASS (klass);
+  GeglOperationPointFilterClass *point_filter_class =
+    GEGL_OPERATION_POINT_FILTER_CLASS (klass);
+
+  operation_class->prepare = prepare;
+  operation_class->opencl_support = FALSE;
+
+  point_filter_class->process    = process;
+
+  gegl_operation_class_set_keys (operation_class,
+    "name",        "dt:exposure",
+    "title",       _("Exposure"),
+    "categories",  "color",
+    "description", _("An implementation of Darktable's exposure filter."),
+    NULL);
+}
+
+#endif
diff --git a/po/POTFILES.in b/po/POTFILES.in
index 10654dc..f5f7913 100644
--- a/po/POTFILES.in
+++ b/po/POTFILES.in
@@ -230,6 +230,7 @@ operations/workshop/bilateral-filter-fast.c
 operations/workshop/demosaic-bimedian.c
 operations/workshop/demosaic-simple.c
 operations/workshop/ditto.c
+operations/workshop/dt-exposure.c
 operations/workshop/external/gluas.c
 operations/workshop/external/lens-correct.c
 operations/workshop/external/line-profile.c