delbetu / prawn_box

PDF Ruby-Prawn previewer running on WebAssembly

Website

https://delbetu.github.io/prawn_box/

Getting started

To run the application locally, you should:

• bundle install to install the Ruby dependencies.
• bundle exec rake to build the .wasm application file.
• bundle exec rake build_site to build the site inti ./dist
• ruby -run -e httpd './dist' -p 8000 serve the site from dist.
• Open a browser at localhost:8000.

Contributing

The system is composed of:

app.wasm ==> ruby interpreter + gems installed into a virtual file system and compiled to wasm Gemfile ==> Hold dependencies (prawn, prawn-table) to be included in app.wasm Rakefile ==> app.wasm task holds the building process for app.wasm index.html ==> UI (creates a webassembly module for app.wasm using ruby-wasm-wasi npm package from ruby.wasm)

How pdf generation works

The main view needs to eval ruby code using the prawn library.

require "rubygems"
$:.unshift("/lib") # virtual file system has this folder with prawn and prawn-table
require "prawn"
require "prawn/table"

pdf = Prawn::Document.new
pdf.instance_eval do
  text "Hello World!"
end
pdf.render

For that, it reads the html input (user ruby code) and calls RubyVm.eval(...). The RubyVm actually is a prepared environment containing. The interpreter ruby.wasm and other gems (prawn and prawn-table). This ruby.wasm executes the ruby code and returns a binary string (the pdf) index.html receives that string and puts it that into the <embed> tag.