EXO中图标透明的小例子

/**
 * exo_gdk_pixbuf_lucent:
 * @source  : the source #GdkPixbuf.
 * @percent : the percentage of translucency.
 *
 * Returns a version of @source, whose pixels translucency is
 * @percent of the original @source pixels.
 *
 * The caller is responsible to free the returned object
 * using g_object_unref() when no longer needed.
 *
 * Returns: a translucent version of @source.
 *
 * Since: 0.3.1.3
 **/
GdkPixbuf*
exo_gdk_pixbuf_lucent (const GdkPixbuf *source,
                       guint            percent)
{
  GdkPixbuf *dst;
  guchar    *dst_pixels;
  guchar    *src_pixels;
  guchar    *pixdst;
  guchar    *pixsrc;
  gint       dst_row_stride;
  gint       src_row_stride;
  gint       width;
  gint       height;
  gint       i, j;

  g_return_val_if_fail (GDK_IS_PIXBUF (source), NULL);
  g_return_val_if_fail ((gint) percent >= 0 && percent <= 100, NULL);

  /* determine source parameters */
  width = gdk_pixbuf_get_width (source);
  height = gdk_pixbuf_get_height (source);

  /* allocate the destination pixbuf */
  dst = gdk_pixbuf_new (gdk_pixbuf_get_colorspace (source), TRUE, gdk_pixbuf_get_bits_per_sample (source), width, height);

  /* determine row strides on src/dst */
  dst_row_stride = gdk_pixbuf_get_rowstride (dst);
  src_row_stride = gdk_pixbuf_get_rowstride (source);

  /* determine pixels on src/dst */
  dst_pixels = gdk_pixbuf_get_pixels (dst);
  src_pixels = gdk_pixbuf_get_pixels (source);

  /* check if the source already contains an alpha channel */
  if (G_LIKELY (gdk_pixbuf_get_has_alpha (source)))
    {
      for (i = height; --i >= 0; )
        {
          pixdst = dst_pixels + i * dst_row_stride;
          pixsrc = src_pixels + i * src_row_stride;

          for (j = width; --j >= 0; )
            {
              *pixdst++ = *pixsrc++;
              *pixdst++ = *pixsrc++;
              *pixdst++ = *pixsrc++;
              *pixdst++ = ((guint) *pixsrc++ * percent) / 100u;
            }
        }
    }
  else
    {
      /* pre-calculate the alpha value */
      percent = (255u * percent) / 100u;

      for (i = height; --i >= 0; )
        {
          pixdst = dst_pixels + i * dst_row_stride;
          pixsrc = src_pixels + i * src_row_stride;

          for (j = width; --j >= 0; )
            {
              *pixdst++ = *pixsrc++;
              *pixdst++ = *pixsrc++;
              *pixdst++ = *pixsrc++;
              *pixdst++ = percent;
            }
        }
    }

  return dst;
}