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#include <glib.h>
#include <gdk-pixbuf/gdk-pixbuf.h>
#include <cairo.h>

/* RGBA image */
/*#define INPUT  "Exhausted.gif" */

/* RGB image */
#define INPUT  "Exhausted.jpg"

#define OUTPUT "out.png"


static cairo_surface_t *
convert_pixbuf_to_cairo_surface (GdkPixbuf *pixbuf)
{
  /* Pixbuf properties */
  int w = gdk_pixbuf_get_width (pixbuf),
      h = gdk_pixbuf_get_height (pixbuf),
      p_stride = gdk_pixbuf_get_rowstride (pixbuf),
      ch = gdk_pixbuf_get_n_channels (pixbuf);
  unsigned char *p_pixels = gdk_pixbuf_get_pixels (pixbuf);

  /* Equavalent cairo props */
  cairo_surface_t *surface;
  int c_stride;
  unsigned char *c_pixels;
  cairo_format_t format;

  /* Initialize properties */
  if (ch == 3)
    format = CAIRO_FORMAT_RGB24;
  else
    format = CAIRO_FORMAT_ARGB32;

  surface = cairo_image_surface_create (format, w, h);
  c_stride = cairo_image_surface_get_stride (surface);
  c_pixels = cairo_image_surface_get_data (surface);

  /* Loop that copies the pixels */
  if (ch == 3) /* RGB image */
    {
      int i;
      for (i = 0; i < h; i++)
        {
          unsigned char *pp = p_pixels + i * p_stride,
                        *pc = c_pixels + i * c_stride;
          int j;
          for (j = 0; j < w; j++)
            {
#if G_BYTE_ORDER == G_LITTLE_ENDIAN
              /* RGB -> BGR(A) */
              pc[0] = pp[2];
              pc[1] = pp[1];
              pc[2] = pp[0];
#else
              /* RGB -> (A)RGB */
              pc[1] = pp[0];
              pc[2] = pp[1];
              pc[3] = pp[2];
#endif
              pc += 4;
              pp += 3;
            }
        }
    }
  else /* RGBA image - rounding is not 100% right */
    {
      int i;
      for (i = 0; i < h; i++)
        {
          unsigned char *pp = p_pixels + i * p_stride,
                        *pc = c_pixels + i * c_stride;
          int j;
          for (j = 0; j < w; j++)
            {
#if G_BYTE_ORDER == G_LITTLE_ENDIAN
              /* RGBA -> BGRA */
              pc[0] = (pp[2] * pp[3] + 0x7f) / 0xff;
              pc[1] = (pp[1] * pp[3] + 0x7f) / 0xff;
              pc[2] = (pp[0] * pp[3] + 0x7f) / 0xff;
              pc[3] = pp[3];
#else
              /* RGBA -> ARGB */
              pc[0] = pp[3];
              pc[1] = (pp[0] * pp[3] + 0x7f) / 0xff;
              pc[2] = (pp[1] * pp[3] + 0x7f) / 0xff;
              pc[3] = (pp[2] * pp[3] + 0x7f) / 0xff;
#endif
              pc += 4;
              pp += 4;
            }
        }
    }

  return surface;
}


int
main (int    argc,
      char **argv)
{
  GdkPixbuf *pixbuf;
  cairo_surface_t *surf;

  g_type_init ();

  pixbuf = gdk_pixbuf_new_from_file (INPUT, NULL);
  g_print ("Channels: %d\n", gdk_pixbuf_get_n_channels (pixbuf));
  surf = convert_pixbuf_to_cairo_surface (pixbuf);

  /* You can now do just about anything you want using cairo */

  cairo_surface_write_to_png (surf, OUTPUT);

  return 0;
}

PKGS=glib-2.0 gdk-pixbuf-2.0 cairo
CFLAGS=-ggdb -Wall `pkg-config --cflags ${PKGS}`
LDFLAGS=-ggdb -Wall `pkg-config --libs ${PKGS}`


all: stamp

clean:
   rm -f stamp *.o