Text width and height based on number of characters / lines displayed

[vikigenius]

So I am trying to develop a card like item that contains long texts, that can be expanded on a button click.

Currently I limit the size of the card by fixing the number of characters I display. (Can just take a slice). Then on button click I just change the text.

        let ctext = if self.expanded { self.text.clone() } else { self.text[..MAX_RENDER_CHARS].to_owned() };

But what if I want to fix the number of lines that I want to display? Say I want to display the first 4 lines?

Equivalently, how do I determine the number of characters that will fit in a single line given width and height of the text element? Is this possible?