Generating PDFs (HTML-to-PDF)

Introduction

Azul can render a styled Dom to a PDF the same way it lays out a window - headless, through the layout engine - and hand you the PDF as bytes. This is the „HTML-to-PDF“ use case: you build your document as a Dom with CSS (headings, tables, images, page breaks), call one function, and get a U8Vec. It is completely decoupled from the window - no App, no event loop - and does no file I/O: you receive the bytes and save / upload / stream them yourself. (This mirrors the printpdf-WASM API: dom -> PDF pages.)

The API

Pdf is a tiny stateless handle (azul::misc::Pdf):

use azul::misc::Pdf;

// `doc` is any styled Dom. Page size is in pixels at 96 DPI:
//   A4     = 794 x 1123    Letter = 816 x 1056
let bytes = Pdf::new().from_dom(doc, 794.0, 1123.0);   // -> U8Vec

// You own the bytes - persist them however you like:
std::fs::write("out.pdf", bytes.as_slice()).unwrap();

The free function dom_to_pdf(dom, page_width_px, page_height_px) -> U8Vec does the same thing without constructing a handle.

Content taller than one page is paginated automatically: the headless layout splits the document across as many pages as it needs, each page_width_px x page_height_px.

A complete example

examples/azul-doc is the P5 goal app. Its export callback builds the document Dom and exports it - no window involved in the conversion:

fn doc_page() -> Dom {
    Dom::create_body()
        .with_child(Dom::create_text("Invoice #42").with_css("font-size: 32px;"))
        .with_child(/* ... tables, paragraphs, images ... */)
}

extern "C" fn on_export(mut data: RefAny, _info: CallbackInfo) -> Update {
    if let Some(s) = data.downcast_ref::<DocState>() {
        let bytes = Pdf::new().from_dom(doc_page(), 794.0, 1123.0); // A4 @ 96 DPI
        let _ = std::fs::write(&s.export_path, bytes.as_slice());
    }
    Update::DoNothing
}

Because the conversion is headless, you can also generate PDFs from a server, a CLI, or a background Thread - anywhere you can build a Dom.

The JSON model

For programmatic / advanced PDF construction you can go through the printpdf JSON representation: pdf.write_json(json) -> U8Vec serializes a document model to PDF bytes, and pdf.read_json(bytes) -> Json parses an existing PDF back into the model. from_dom is the high-level path; write_json is the escape hatch when you need to place content the layout engine wouldn't.

Feature gating