Simple text reading app

I am writing program for reading the texts. I wish to add in TextEditor class possibility of highlight the text background. The problem is not very difficult, but information on the coordinates in which each letter is hidden deep in the class.
What do you think is easier to add to the possibility of highlight TextEditor text background?

That is a bit tricky to do with the text editor, it’d probably need some changes to make it easy. I’ll look into it when I get chance.