Thunar 1.0.0 中是怎么进行图片预览的 （二）

上一章介绍的是图片预览的主要实现方式，这次来介绍下Thunar实现预览的流程。

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./thunar/thunar-icon-factory.c获取文件的图标 thunar_icon_factory_load_file_icon()。

对于已经存在缩略图的查找缩略图thunar_vfs_thumb_factory_lookup_thumbnail()，

判断其修改时间和缩略图修改时间是否一致thunar_vfs_thumbnail_is_valid()，不一致则重新生成 。

如果找不到缩略图，或者需要重新生成缩略图的文件，调用thunar_thumbnail_generator_enqueue()。

最后，生成缩略图后当作文件的图标。

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./thunar/thunar-thumbnail-generator.c中开辟一个新线程来进行缩略图的生成：
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/** * thunar_vfs_thumbnail_is_valid: * @thumbnail : the absolute path to a thumbnail file. * @uri       : the URI of the original file. * @mtime     : the modification time of the original file. * * Checks whether the file located at @thumbnail contains a * valid thumbnail for the file described by @uri and @mtime. * * The usage of this method is thread-safe. * * Return value: %TRUE if @thumbnail is a valid thumbnail for *               the file referred to by @uri, else %FALSE. **/gbooleanthunar_vfs_thumbnail_is_valid (const gchar      *thumbnail,                               const gchar      *uri,                               ThunarVfsFileTime mtime){  png_structp  png_ptr;  png_infop    info_ptr;  png_textp    text_ptr;  gboolean     is_valid = FALSE;  gchar        signature[4];  FILE        *fp;  gint         n_checked;  gint         n_text;  gint         n;  g_return_val_if_fail (g_path_is_absolute (thumbnail), FALSE);  g_return_val_if_fail (uri != NULL && *uri != '\0', FALSE);  /* try to open the thumbnail file */  fp = fopen (thumbnail, "r");  if (G_UNLIKELY (fp == NULL))    return FALSE;  /* read the png signature */  if (G_UNLIKELY (fread (signature, 1, sizeof (signature), fp) != sizeof (signature)))    goto done0;  /* verify the png signature */  if (G_LIKELY (png_check_sig ((png_bytep) signature, sizeof (signature))))    rewind (fp);  else    goto done0;  /* allocate the png read structure */  png_ptr = png_create_read_struct (PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);  if (G_UNLIKELY (png_ptr == NULL))    goto done0;  /* allocate the png info structure */  info_ptr = png_create_info_struct (png_ptr);  if (G_UNLIKELY (info_ptr == NULL))    {      png_destroy_read_struct (&png_ptr, NULL, NULL);      goto done0;    }  /* read the png info from the file */  png_init_io (png_ptr, fp);  png_read_info (png_ptr, info_ptr);  /* verify the tEXt attributes defined by the thumbnail spec */  n_text = png_get_text (png_ptr, info_ptr, &text_ptr, &n_text);  for (n = 0, n_checked = 0; n_checked < 2 && n < n_text; ++n)    {      if (strcmp (text_ptr[n].key, "Thumb::MTime") == 0)        {          /* verify the modification time */          if (G_UNLIKELY (strtol (text_ptr[n].text, NULL, 10) != mtime))            goto done1;          ++n_checked;        }      else if (strcmp (text_ptr[n].key, "Thumb::URI") == 0)        {          /* check if the URIs are equal */          if (strcmp (text_ptr[n].text, uri) != 0)            goto done1;          ++n_checked;        }    }  /* check if all required attributes were checked successfully */  is_valid = (n_checked == 2);done1:  png_destroy_read_struct (&png_ptr, &info_ptr, NULL);done0:  fclose (fp);  return is_valid;}
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