[C][gegl][tool] convert image to PNG thumbnail

geglthumbnail.c

/* make PNG thumbnail by gegl: http://gegl.org/
 *
 * build:
 * gcc -Wall `pkg-config --cflags --libs gegl` geglthumbnail.c -o geglthumbnail
 *
 * usage:
 * ./geglthumbnail image.xxx thumbnail.png
 *
 */
#include <glib.h>
#include <glib/gprintf.h>
#include <gegl.h>

gint main(gint argc, gchar * argv[])
{
  gchar * infile;
  gchar * thumbfile;
  gint thumbwidth = 200;
  gint thumbheight = 150;


  gegl_init(&argc, &argv);
  if (argc < 3) return -1;
  infile = argv[argc - 2];
  thumbfile = argv[argc - 1];

  {
    GeglNode * gegl;
    GeglNode * input;
    GeglNode * output;
    GeglNode * filter;
    GeglRectangle bb;
    // root node
    gegl = gegl_node_new();
    // operations specs see: http://gegl.org/operations.html
    input = gegl_node_new_child(gegl,
                                "operation", "gegl:load",
                                "path", infile,
                                NULL);
    bb = gegl_node_get_bounding_box(input);
    //g_printf("%d %d\n", bb.height, bb.width);
    output = gegl_node_new_child(gegl,
                                 "operation", "gegl:png-save",
                                 "path", thumbfile,
                                 NULL);
    // thumbnail filter
    filter = gegl_node_new_child(gegl,
                                 "operation", "gegl:scale",
                                 "filter", "cubic",
                                 "x", (thumbwidth - 2) / (gdouble) bb.width,
                                 "y", (thumbheight - 2) / (gdouble) bb.height,
                                 NULL);
    // connect as: input -> filter -> output
    gegl_node_link_many(input, filter, output, NULL);

    // process image from input to output
    gegl_node_process(output);

    g_object_unref(gegl);
  }
  gegl_exit();
  return 0;
}