# ../operations/common/brightness-contrast.c

    /* 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 Øyvind Kolås <pippin@gimp.org>
     */

    #include "config.h"
    #include <glib/gi18n-lib.h>

    /* Followed by this #if ... */
    #ifdef GEGL_CHANT_PROPERTIES
    /* ... are the properties of the filter, these are all scalar values
     * (doubles), the the parameters are:
     *       property name,   min,   max, default, "description of property"
     */

    gegl_chant_double (contrast, _("Contrast"), -5.0, 5.0, 1.0,
                       _("Range scale factor"))
    gegl_chant_double (brightness, _("Brightness"), -3.0, 3.0, 0.0,
                       _("Amount to increase brightness"))

    /* this will create the instance structure for our use, and register the
     * property with the given ranges, default values and a comment for the
     * documentation/tooltip.
     */
    #else

    /* Specify the base class we're building our operation on, the base
     * class provides a lot of the legwork so we do not have to. For
     * brightness contrast the best base class is the POINT_FILTER base
     * class.
     */
    #define GEGL_CHANT_TYPE_POINT_FILTER

    /* We specify the file we're in, this is needed to make the code
     * generation for the properties work.
     */
    #define GEGL_CHANT_C_FILE       "brightness-contrast.c"

    /* Including gegl-chant.h creates most of the GObject boiler plate
     * needed, creating a GeglChant instance structure a GeglChantClass
     * structure for our operation, as well as the needed code to register
     * our new gobject with GEGL.
     */
    #include "gegl-chant.h"

    /* prepare() is called on each operation providing data to a node that
     * is requested to provide a rendered result. When prepare is called
     * all properties are known. For brightness contrast we use this
     * opportunity to dictate the formats of the input and output buffers.
     */
    static void prepare (GeglOperation *operation)
    {
      gegl_operation_set_format (operation, "input", babl_format ("RGBA float"));
      gegl_operation_set_format (operation, "output", babl_format ("RGBA float"));
    }

    /* For GeglOperationPointFilter subclasses, we operate on linear
     * buffers with a pixel count.
     */
    static gboolean
    process (GeglOperation       *op,
             void                *in_buf,
             void                *out_buf,
             glong                n_pixels,
             const GeglRectangle *roi)
    {
      /* Retrieve a pointer to GeglChantO structure which contains all the
       * chanted properties
       */
      GeglChantO *o = GEGL_CHANT_PROPERTIES (op);
      gfloat     *in_pixel;
      gfloat     *out_pixel;
      gfloat      brightness, contrast;
      glong       i;

      in_pixel   = in_buf;
      out_pixel  = out_buf;

      brightness = o->brightness;
      contrast   = o->contrast;

      for (i=0; i<n_pixels; i++)
        {
          gint component;
          for (component=0; component <3 ; component++)
            {
              out_pixel[component] =
                    (in_pixel[component] - 0.5) * contrast + brightness + 0.5;
            }
          out_pixel[3] = in_pixel[3]; /* copy the alpha */
          in_pixel  += 4;
          out_pixel += 4;
        }
      return TRUE;
    }

    #ifdef HAS_G4FLOAT
    /* The compiler supports vector extensions allowing an version of
     * the process code that produces more optimal instructions on the
     * target platform.
     */

    static gboolean
    process_simd (GeglOperation       *op,
                  void                *in_buf,
                  void                *out_buf,
                  glong                samples,
                  const GeglRectangle *roi)
    {
      GeglChantO *o   = GEGL_CHANT_PROPERTIES (op);
      g4float    *in  = in_buf;
      g4float    *out = out_buf;

      /* add 0.5 to brightness here to make the logic in the innerloop tighter
       */
      g4float  brightness = g4float_all(o->brightness + 0.5);
      g4float  contrast   = g4float_all(o->contrast);
      g4float  half       = g4float_half;

      while (samples--)
        {
          *out = (*in - half) * contrast + brightness;
          g4floatA(*out)=g4floatA(*in);
          in  ++;
          out ++;
        }
      return TRUE;
    }
    #endif

    /*
     * The class init function sets up information needed for this operations class
     * (template) in the GObject OO framework.
     */
    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);

      /* override the prepare methods of the GeglOperation class */
      operation_class->prepare = prepare;
      /* override the process method of the point filter class (the process methods
       * of our superclasses deal with the handling on their level of abstraction)
       */
      point_filter_class->process = process;

      /* specify the name this operation is found under in the GUI/when
       * programming/in XML
       */
      operation_class->name        = "gegl:brightness-contrast";

      /* a colon separated list of categories/tags for this operations */
      operation_class->categories  = "color";

      /* a description of what this operations does */
      operation_class->description = _("Changes the light level and contrast.");

    #ifdef HAS_G4FLOAT
      /* add conditionally compiled variation of process(), gegl should be able
       * to determine which is fastest and hopefully if any implementation is
       * broken and not conforming to the reference implementation.
       */
      gegl_operation_class_add_processor (operation_class,
                                          G_CALLBACK (process_simd), "simd");
    #endif
    }

    #endif /* closing #ifdef GEGL_CHANT_PROPERTIES ... else ... */