/// <summary>
/// Renders the Gif Comment to a Comment Extension Block which can be
/// embedded in a Gif file.
/// </summary>
/// <returns>
/// A <see cref="ByteVector"/> with the Comment Extension Block for the
/// Gif Comment, or <see langword="null" /> if the file does not have
/// a Gif Comment.
/// </returns>
private ByteVector RenderGifCommentBlock()
{
// Check, if GifCommentTag is contained
GifCommentTag comment_tag = GetTag(TagTypes.GifComment) as GifCommentTag;
if (comment_tag == null)
{
return(null);
}
string comment = comment_tag.Comment;
if (comment == null)
{
return(null);
}
ByteVector comment_data = new ByteVector();
// Add Extension Introducer (0x21) and Comment Label (0xFE)
comment_data.Add(new byte [] { 0x21, 0xFE });
// Add data of comment in sub-blocks of max length 256.
ByteVector comment_bytes = new ByteVector(comment);
byte block_max = 255;
for (int start = 0; start < comment_bytes.Count; start += block_max)
{
byte block_length = (byte)Math.Min(comment_bytes.Count - start, block_max);
comment_data.Add(block_length);
comment_data.Add(comment_bytes.Mid(start, block_length));
}
comment_data.Add(new byte [] { 0x00 });
return(comment_data);
}
/// <summary>
/// Gets a tag of a specified type from the current instance,
/// optionally creating a new tag if possible.
/// </summary>
/// <param name="type">
/// A <see cref="TagLib.TagTypes" /> value indicating the
/// type of tag to read.
/// </param>
/// <param name="create">
/// A <see cref="bool" /> value specifying whether or not to
/// try and create the tag if one is not found.
/// </param>
/// <returns>
/// A <see cref="Tag" /> object containing the tag that was
/// found in or added to the current instance. If no
/// matching tag was found and none was created, <see
/// langword="null" /> is returned.
/// </returns>
public override TagLib.Tag GetTag (TagLib.TagTypes type,
bool create)
{
foreach (Tag tag in ImageTag.AllTags) {
if ((tag.TagTypes & type) == type)
return tag;
}
if (!create || (type & ImageTag.AllowedTypes) == 0)
return null;
ImageTag new_tag = null;
switch (type) {
case TagTypes.JpegComment:
new_tag = new JpegCommentTag ();
break;
case TagTypes.GifComment:
new_tag = new GifCommentTag ();
break;
case TagTypes.Png:
new_tag = new PngTag ();
break;
case TagTypes.TiffIFD:
new_tag = new IFDTag ();
break;
case TagTypes.XMP:
new_tag = new XmpTag ();
break;
}
if (new_tag != null) {
ImageTag.AddTag (new_tag);
return new_tag;
}
throw new NotImplementedException (String.Format ("Adding tag of type {0} not supported!", type));
}
