The Page Order Math Behind Saddle-Stitch Booklets Is Weirder Than You Think. So I Automated It. [Devlog #8]

pub fn compute_imposition(total_pages: u32) -> Vec<(u32, u32, u32, u32)> {

    // Round up to nearest multiple of 4

    let padded = ((total_pages + 3) / 4) * 4;

    let sheets = padded / 4;

    let mut layout: Vec<(u32, u32, u32, u32)> = Vec::new();



    for i in 0..sheets {

        let front_right = i + 1;

        let front_left = padded - i;

        let back_left = i + 2;

        let back_right = padded - i - 1;



        // (front_left, front_right, back_left, back_right)

        layout.push((front_left, front_right, back_left, back_right));

    }



    layout

}

pub fn build_imposition_pdf(

    original: &Document,

    layout: &[(u32, u32, u32, u32)],

) -> Result {

    let mut new_doc = Document::with_version("1.5");



    for (front_left, front_right, back_left, back_right) in layout {

        add_sheet(&mut new_doc, original, *front_left, *front_right)?;

        add_sheet(&mut new_doc, original, *back_left, *back_right)?;

    }



    Ok(new_doc)

}

pub fn detect_headings(doc: &Document) -> Vec<(u32, String)> {

    let mut headings: Vec<(u32, String)> = Vec::new();



    for (page_num, _) in doc.get_pages() {

        if let Ok(text) = doc.extract_text(&[page_num]) {

            let first_line = text.lines().next().unwrap_or("").trim();



            if first_line.len() > 2

                && first_line.len() < 60

                && !first_line.ends_with('。')

                && !first_line.ends_with('.')

            {

                headings.push((page_num, first_line.to_string()));

            }

        }

    }



    headings

}