TextLayout getAscent getDescent

Question

I'am actually using TextLayouts to display. I create a textLayout for each line of my text and place them using getAscent() and getDescent() methods.

All the line of the text are using the same police, so the different textLayouts too. I would like to know if the getAscent() et getDescent() are constants for a given police. Or if they can changes with the content of the TextLayout.

Thanks for help.