Arrolio

FOP-like paged layout engine for Ruby. Renders to PDF via the sibling pdfrb gem.

What this is

Arrolio is the middle layer of a three-library stack:

Library	Owns	Depends on
`pdfrb`	Pure-Ruby PDF library (bytes ↔ model; streams, fonts, xref, encryption)	—
`arrolio` (this gem)	FOP-like paged layout: page templates, threaded flows, Knuth-Plass line/page breaking, tables, lists, SVG, page-model selection, running headers/footers	`pdfrb`
`loom` (separate gem, not yet built)	Multi-target layout compiler. Compiles a higher-level DSL to Arrolio’s IR, plus CSS, XSL-FO, and IDML.	`arrolio` (for the PDF target only)

Arrolio’s job: take a content tree plus a layout spec, produce a sequence of laid-out pages, render those to PDF (or, in future, to other paged formats).

Two-direction contract

Content + LayoutSpec → Arrolio::Engine::Paged → Output::Page[] (the layout pass).
Output::Page[] → Arrolio::Renderer::Pdf → bytes (the render pass; uses Pdfrb internally).

Quick start

require "arrolio"

content = Arrolio::Content::Document.new
content.add_section("Introduction", level: 1) do |section|
  section.add_paragraph("Hello, World!")
end

layout = Arrolio::LayoutSpec.new
layout.add_page_template(:body, page_size: :A4, margins: 25)
layout.add_style(:body, font: "Times-Roman", size: 11)

engine   = Arrolio::Engine::Paged.new(layout)
pages    = engine.layout(content)
renderer = Arrolio::Renderer::Pdf.new

File.binwrite("out.pdf", renderer.render(pages))

Higher-level convenience API:

Arrolio.compose("out.pdf") do |doc|
  doc.page_size = :A4
  doc.margins   = 25
  doc.heading "Introduction"
  doc.text   "Hello, World!"
end

Where Arrolio’s responsibilities end

Arrolio deliberately does not own:

PDF byte format — that’s Pdfrb’s job.
DSL authoring (YAML, FO XML, etc.) — that’s Loom’s job.
Multi-target compilation (CSS / XSL-FO / IDML) — Loom.
The semantic content model — that’s metanorma-document (or any conforming source). Arrolio defines a contract, not an implementation.

Status

Pre-1.0. The skeleton lands first; modules port incrementally from Pdfrb::Layout::* (which will eventually be removed from Pdfrb once Arrolio is stable).

License

BSD-2-Clause. See LICENSE.

arrolio