itext7-dotnet | NET version of the iText library | Document Editor library

Depending on the font and the diacritical mark in question the font may not contain each needed combination of character and mark as glyph. Instead there may merely be an individual glyph with the mark in question, and a character with that mark is drawn by drawing the character glyph and the mark glyph at the same position.

To allow them to be drawn at the same position, the glyph of the mark, albeit not actually having a zero width, when drawn does not advance the glyph drawing position.

Furthermore, a diacritical mark may have to be drawn at different heights depending on the character it is combined with, in particular if the character is combined with multiple marks.

In the context of your question, therefore, ...

If a text chunk has no diagonal line length, wouldn't that mean the text chunk is empty, and thus it's a moot point to wonder if it is or isn't on the same line?

If a diacritical mark glyph is combined with a character glyph at a different height than normal, that mark glyph forms a text chunk by itself with a DistPerpendicular value differing from the values of chunks around it on the same line.

As the mark glyph doesn't advance the text insertion point and the length of the chunk baseline essentially is the sum of the character advancements of the drawn glyphs, the length of a chunk containing only a diacritical mark, is 0.

To recognize such a situation, therefore, iText checks whether the DistPerpendicular difference, albeit not 0, is not too large, and whether one of these chunks in question has zero length: