Find positions of letters in a RichTextLable

Hi, I am trying to find the position of each letter in a richTextLable. I am trying to find the beginning and end of each letter. The reason i want this is because i am makin a hangman like game where i want to draw a line2d under each letter, and then make some of the letters transparent. I have tried to use Font.get_string_size() for each letter in the text, but since letters change size depending on the letters they are next to, believe its called kerning, get_string_size gives a diffrent result on a substring than for the full string. get_line_offset and get_ascent gives me y position, so its only the x position i having problems with