Function zaplib::get_font_atlas_page_id

pub fn get_font_atlas_page_id(
    fonts_data: &RwLock<CxFontsData>, 
    font_id: usize, 
    dpi_factor: f32, 
    font_size: f32
) -> (usize, RwLockReadGuard<'_, CxFontsData>)

Get the page id for a particular font_id/dpi_factor/font_size combination.

Returns a read lock in addition to the page id, since you typically need to read more stuff out of fonts_data, and this avoids you having to get another lock after this.