Hadar

Markdown-backed slide decks with source-preserving editing, live preview, and presentation export.

Website · User Guide · Features · Installation · Quick start

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Hadar is a Ruby presentation library built around ordinary Markdown files. Beid keeps the source-positioned document as the editable copy; Hadar projects it into slides, slots, and a live Zaniah preview. Embed a presentation window in an app or export a deck without a GUI.

Features

• Eight automatic or explicitly selected slide templates, plus opt-in freeform placement.
• Source-backed text, image, table-cell, and fenced-code editing with speaker notes.
• Three built-in JSONC themes (minimal, dark, warm) and custom themes.
• Virtualized slide thumbnails, keyboard navigation, a command palette, and a secondary-display presenter view.
• Searchable PDF, PNG-sequence, and animated PNG (APNG) export.

Installation

Use CRuby 3.2 or newer. Install the gem, or add gem "hadar" to your Gemfile and run bundle install:

gem install hadar

Hadar is a library; it does not install a hadar command. Windowed use requires a Zaniah-supported display backend. PNG and APNG export use Zaniah's headless renderer.

Quick start

Save this as slides.md. The initial YAML front matter selects a theme; later Markdown thematic breaks separate slides:

---
theme: dark
---
# Quarterly report

## 2026 Q3

---

<!-- layout: two-column -->
# Revenue

::: left
Revenue rose 18% year over year.
:::

::: right
New customers: 42
:::

Save the following as present.rb beside the deck, then run ruby present.rb (or bundle exec ruby present.rb in a Bundler project):

require "hadar"

deck = Hadar::Deck.open(File.join(__dir__, "slides.md"))
app = Hadar::Application.new(deck)
window = Zaniah::Platform.open_window(title: "Hadar")
app.attach(main_window: window)
app.run

Select a thumbnail and a slot to edit. Arrow keys and Page Up/Down navigate slides. P or F5 toggles presentation, F11 toggles fullscreen, and Escape exits these modes. Ctrl/Cmd-K opens the command palette; Ctrl/Cmd-S saves an opened deck. With a second display, Hadar opens a presenter view with notes, the next slide, and elapsed time.

For headless export:

require "hadar"

deck = Hadar::Deck.open("slides.md")
Hadar::Export::PDF.write(deck, "slides.pdf", font: "/path/to/font.ttf")
Hadar::Export::PNGSequence.write(deck, "slides-png", width: 1280, height: 720)
Hadar::Export::APNG.write(deck, "slides.apng", duration_ms: 2500)

Replace the PDF font path with a TrueType-outline font covering the deck's text, or omit font: to use Zaniah's local font database. PDF embeds local PNG/JPEG images and replaces an existing output file. PNG sequences refuse existing frames; APNG requires overwrite: true to replace a file. See export for format options and limits.

Editing and limits

Edits write back to Markdown through Beid. Opened decks save atomically and refuse to overwrite external changes. Successful edits replace slot snapshots; fetch the slot again before the next edit. The application reloads external changes when there are no competing unsaved edits.

Rich-text edits support source-backed text runs, simple bold/italic changes, and one-level list indentation. Structural changes and unsupported styles are rejected. Tables and fenced code have dedicated editors. Image references remain local paths; assets are not copied. Freeform positions are explicit Markdown comments and lose their placement in a plain Markdown viewer. See editing and presenting and layouts.

Documentation

• User Guide — installation and your first deck.
• Editing and presenting — slots, keyboard controls, save/reload, and notes.
• Layouts and Markdown — templates, slide syntax, and freeform placement.
• Themes — built-in styles and custom JSONC themes.
• Export — searchable PDF, PNG sequences, and APNG.
• Development — tests, source structure, and website maintenance.
• Changelog

Development

bundle install
bundle exec rake

Check the 100-slide thumbnail layout/scene-build budget with BUDGET=1 bundle exec ruby bench/slide_list.rb. See the development guide for type checks and website previews, and the template-layout and freeform-placement decisions for the source model.

License

Hadar is released under the MIT License.