The Devver Blog

What is Processing?

"Processing is an open source programming language and environment for people who want to program images, animation, and interactions."
-Processing.org

I wanted to play around with doing some visual programming and had played with Processing in the past. I recently had been reading about Ruby-Processing and wanted to give it a shot. First, I went to look for some Ruby-Processing tutorials, and I had recently heard about the presentation by Jeff Casimir about the 'Art of Code' (slides and code), using Ruby-Processing. I went through those examples and decided I wanted to modify it to display snowflakes in the spirit of winter. After a bit of searching I found a project that generated a Penrose snow flake using Ruby-Processing. I figured I could modify the programs to get a nice snow flake screen saver type app. The result is my app Processing-Snow, and is shown in the screen shot below.

Processing-Snow

Playing around with Ruby-Processing is a lot of fun, I highly recommend spending a couple hours to make a tiny app. I built my Snow app in about an hour and a half. Then I spent a bit of time using Caliper to improve the metrics. For such a small project there wasn't a lot to improve, but it still helped me to do some refactoring. To get an idea of the code you can view Processing-Snow's Metrics.

Feel free to fork Processing-Snow on GitHub and read about how to run it with in the projectss README.

According to the Sinatra FAQ, source reloading was taken out of Sinatra in version 0.9.2 due to "excess complexity" (in my opinion, that's a great idea, because it's not a feature that needs to be in minimal a web framework like Sinatra). Also, according to the FAQ, Rack::Reloader (included in Rack) can be added to a Sinatra application to do source reloading, so I decided to try it out.

Setting up Rack::Reloader is easy:

require 'sinatra'
require 'rack'

configure :development do
  use Rack::Reloader
end

get "/hello" do
  "hi!"
end

$ ruby hello.rb
== Sinatra/0.9.4 has taken the stage on 4567 for development with backup from Thin
>> Thin web server (v1.2.4 codename Flaming Astroboy)
>> Maximum connections set to 1024
>> Listening on 0.0.0.0:4567, CTRL+C to stop
[on another terminal]
$ curl http://localhost:4567/hello
hi!

If you add another route, you can access it without restarting Sinatra:

get "/goodbye" do
  "bye!"
end

$ curl http://localhost:4567/goodbye
bye!

But what happens when you change the contents of a route?

get "/hello" do
  "greetings!"
end

$ curl http://localhost:4567/hello
hi!

You still get the old value! What is going on here?

Rack::Reloader simply looks at all files that have been required and, if they have changed on disk, re-requires them. So each Sinatra route is re-evaluated when a reload happens.

However, identical Sinatra routes do NOT override each other. Rather, the first route that is evaluated is used (more precisely, all routes appended to a list and the first matching one is used, so additional identical routes are never run).

We can see this with a simple example:

require 'sinatra'

get "/foo" do
 "foo"
end

get "/foo" do
 "bar"
end

$ curl http://localhost:4567/foo
foo   # The result is 'foo', not 'bar'

Clearly, Rack::Reloader is not very useful if you can't change the contents of any route. The solution is to throw away the old routes when the file is reloaded using Sinatra::Application.reset!, like so:

configure :development do
  Sinatra::Application.reset!
  use Rack::Reloader
end

$ curl http://localhost:4567/hello
greetings!

Success!

A word of caution: you MUST call reset! very early in your file - before you add any middleware, do any other configuration, or add any routes.

This method has worked well enough for our Sinatra application. However, code reloading is always tricky and is bound to occasionally produce some weird results. If you want to significantly reduce the chances for strange bugs (at the expense of code loading time), try Shotgun or Rerun. Happy reloading!