thumb-gdk.c

   1 /* thumb-gdk.c: load, scale, and save the image using a GDK Pixbuf
   2
   3    Copyright 2011 Lewis Gentry.
   4
   5    This program is free software: you can redistribute it and/or
   6    modify it under the terms of the GNU General Public License as
   7    published by the Free Software Foundation, either version 3 of the
   8    License, or (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful, but
  11    WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  13    General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program. If not, see <http://www.gnu.org/licenses/>. */
  17
  18 #include <gdk-pixbuf/gdk-pixbuf.h>
  19 #include <stdio.h>
  20
  21 /* As soon as we learn the dimensions of the existing cover, this
  22    callback function snaps into play to set the dimensions of the
  23    thumbnail. */
  24
  25 void scale(GdkPixbufLoader *self, gint width, gint height, gpointer reqsize)
  26 {
  27   gint max = GPOINTER_TO_INT(reqsize);
  28
  29   if (width == height)
  30     gdk_pixbuf_loader_set_size(self, max, max);
  31   else if (width < height)
  32     gdk_pixbuf_loader_set_size(self, width * max / height, max);
  33   else
  34     gdk_pixbuf_loader_set_size(self, max, height * max / width);
  35 }
  36
  37 /* Feed a quantity of bytes to dest (an initialized PixbufLoader) from
  38    source (a stream open for reading) and return status. */
  39
  40 int fill(GdkPixbufLoader *dest, FILE *source, unsigned int bytes_remaining)
  41 {
  42   unsigned int stride = 4096;
  43   guchar buffer[stride];
  44
  45   for (; bytes_remaining; bytes_remaining -= stride) {
  46     if (bytes_remaining < stride)
  47       stride = bytes_remaining;
  48     if (fread(buffer, sizeof(guchar), stride, source) != stride
  49         || !gdk_pixbuf_loader_write(dest, buffer, stride, NULL)) {
  50       gdk_pixbuf_loader_close(dest, NULL);
  51       return 0;
  52     }
  53   }
  54   return gdk_pixbuf_loader_close(dest, NULL);
  55 }
  56
  57 /* Read, scale, and save an image. Return true if no mishaps. */
  58
  59 int thumb(FILE *stream, unsigned int n, char *pathname, int requested_size)
  60 {
  61   GdkPixbufLoader *loader;
  62   GdkPixbuf *pixbuf;
  63   int status = 0;
  64
  65   g_type_init(); /* Required before doing gAnything. */
  66   loader = gdk_pixbuf_loader_new();
  67   g_signal_connect(loader, "size_prepared", (GCallback) scale,
  68                    GINT_TO_POINTER(requested_size));
  69
  70   if (fill(loader, stream, n)) {
  71     pixbuf = gdk_pixbuf_loader_get_pixbuf(loader);
  72     if (pixbuf)
  73       status = gdk_pixbuf_save(pixbuf, pathname, "png", NULL, NULL);
  74   }
  75   g_object_unref(loader);
  76   return status;
  77 }