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This project will house a set of educational web apps. Each web app is a single-page application written in HTML5/JavaScript, with a small backend component written in PHP (possibly changing in the near future).

The directory structure houses the custom code and several free & open-source libraries that are used by the code.

A frequently-updated live version of the in-development apps is going to be hosted at

Directory structure

  • Makefile a Makefile that is used to run pre-processing jobs on the code (e.g. convert .less files into .css). Use "make watch" to automatically watch the directory for changes in the background. Use "make devserver" to start a webserver at http://localhost:8000.
  • share/ contains the PHP backend.
    • share/skeleton contains templates for the "header" part of the HTML page (e.g. doctype, head, etc.) and "footer" (closing tags).
  • apps/ is where the apps are housed, and represents the document root of the website.

Setting up a local development environment

(1) Download from; move it to your Applications folder, double click on it, and ensure it runs at startup.

(2) Install MacPorts ( Once MacPorts is installed, ensure that /opt/local/bin is part of the PATH environment variable, e.g. add this line to your bash startup script (~/.bashrc or ~/.bash_profile):

export PATH=/opt/local/bin:/Applications/$PATH

(this also adds the Postgres binaries -- which are contained in the app bundle -- to the PATH).

(3) Install Xcode from the App Store. Accept Xcode's licence from the command line by typing

sudo xcodebuild -license

from a command line.

(4) Install the following software through MacPorts:

sudo port install nodejs php55 php55-postgresql npm

(5) Install the LESS compiler:

sudo npm install -g less

(6) Download the Heroku toolbet (if you haven't already) from here: and run the Installer.

(7) Navigate to the project directory (save-point) and set up Heroku to track the Git repository, if you haven't already:

heroku git:remote -a save-point

(8) Add the following line to your Bash startup script:

export DATABASE_URL="postgres://$(whoami)@localhost:5432/$(whoami)"

(9) Run composer to download required PHP packages: php composer.phar install

(10) Restart your shell(s) to make sure the environment variables are set.

The development lifecycle

(1) Cd to the project directory, make sure to have the most recent version of the repository:

git pull

(2) Make sure is running. To download the current database on Heroku to your local installation, type

make download_db

(3) Open a terminal dedicated to running the local dev server. Type

make devserver

This should (a) start the PHP server and listen for requests, and (b) open the default browser pointing to localhost:8800. That should display the login for the dashboard. To exit the server, type Ctrl-C. Most of the time, you want to have the server always running in the background -- just reload the page in the server to see any changed files.

The server will also echo the path of the files being requested by the web browser.

(4) Open a terminal dedicated to running automated tasks: e.g. translating yaml files to the json format. In that terminal, type

make watch

This will run a process in the background, which runs a few tasks automatically as files are changed. To quit it, type Ctrl-C. Most of the time, you want it running in the background.

(5) Make changes to files and test in the browser. You can also test the website in the iOS simulator by opening Xcode -> Developer tool -> iOS simulator.

(6) Commit and push your changes to GitHub:

git add -A; git commit -am "My commit message"; git push

(7) To see changes in Heroku at, type

git push dev master

This will push the changes to the development server, giving you the chance to test the changes remotely before pushing to the production (i.e. stable version) server.

(8) Optional! Only if you're 100% sure that your changes are not breaking anything on the website, push changes to the stable Heroku address, by typing

git push heroku master

Some useful files

YAML files

YAML is a format used for complex configuration files. It is used inside each app directory (e.g. gravity/app.yaml, dashboard/app.yaml, etc.) to configure each app.

Both the PHP server and the JavaScript code typically read in the content of those files in order to shape the application; e.g. gravity/app.yaml contains a list of missions and their properties. Its contents are translated into data structures in both PHP and JavaScript: e.g., a YAML file that looks like this:

description: Hello!
  - Cute
  - Neat
  - Wise

would be translated into this JavaScript object:

{description: "Hello", properties: ['Cute', 'Neat', 'Wise']}

(e.g. an object with two fields "description" and "properties"; the "properties" field contains an array of three strings). This article: talks about the format. Note that indentation is significant to identify arrays and other structures.

JavaScript cannot natively read YAML, so the make watch process translates YAML files into JSON files in each app directory. JSON is a completely equivalent format, but it is much less readable. The JSON file should never be modified directly, and it might be overwritten by make watch -- instead one should only work on the YAML file.

The app.yaml file for Gravity

Message boxes

In the "help" section, different message boxes can be set up that will pop up on specific events. A typical help section will look like this:


  • on: start message: | Hello there stranger! @proceed

  • on: proceed message: | You clicked next! Good job!

Available events

  • on: start is shown at the beginning of the level.
  • on: proceed is shown when the user clicks on the "Next" button. You can set up multiple on: proceed message boxes, and they will be shown in order.
  • on: change:nplanets is shown when the user adds a planet.
  • on: planet:drag is shown when the user drags a planet.
  • on: planet:dragvelocity is shown when the user drags the velocity vector.
  • on: winX where X is 1, 2, or 3 is the message displayed when the user wins the level with X stars.
  • on: win is shown when the user completes the level, if there is no winX property.
  • on: lose is shown when the user fails to complete the level.

Available tags in the message

Special strings can be inserted in the message that will be translated into non-text content (e.g. the Next button, avatar images, etc) or commands that influence the game (e.g. making the screen non-interactive, make the stars rotate, etc.). These are the tags that are implemented:

  • @fly makes the stars spin
  • @noninteractive ignores clicks from the user on the game area (this is only active for the current help box).
  • @name is the username of the player.
  • @boss, @groknar are the avatars for characters
  • @wait-5, @wait-10 show the message for 5/10 seconds before proceeding to the next message.
  • @hide-5, @hide-10 show the message for 5/10 seconds, then hide the message.
  • @proceed inserts the "Next" button
  • @close inserts the "Close" button
  • *text* makes the text bold.
  • Use two carriage returns to create a paragraph.

How to win a level and computing points

Each level will have two fields, "rule" and "starsrule". "rule" determines whether a level has been cleared or not. The rule will be a single JavaScript expression that evaluates to true or false.

In order to compose a rule, you have access to a few properties:

  • nplanets is the number of planets
  • elements is an array of a list of orbital elements (period, sma, eccentricity are the most useful). For instance, elements[0].eccentricity returns the eccentricity of the first planet.
  • collided is a boolean property reflecting whether there has been a collision before the rule is evaluated.

For the elliptical level, a rule looks like this:

rule: nplanets > 0 && elements[0].eccentricity < 0.99 && !collided

"starsrule" returns a number between 1 and 3, reflecting the number of stars earned by the user. It should again be a single JavaScript expression. The ternary expression in JavaScript is useful for that purpose: (cond ? return1 : return2) returns "return1" if cond is true, "return2" otherwise. It can be nested, too. A starsrule for the elliptical level looks like this:

starsrule: |
  (elements[0].eccentricity < 0.4 ? 1 : (elements[0].eccentricity < 0.7 ? 2 : 3))

(notice that the rule itself is on a separate line preceded by the pipe character -- this is because the rule contains a colon character, which is a reserved character for YAML keys -- the pipe character introduces an "as-is" string). The expression evaluates to 1 if the eccentricity is < 0.4, 2 if < 0.7, 3 otherwise.

Level properties

Aside from the starsrule and rule properties, there are a few additional properties:

  • title: the title of the level (main message)
  • name: the name of the level (a unique string), used in maps.yaml to connect levels together.
  • icon: name of the icon
  • music: the music for the level
  • value: used to evaluate the stars value of a level (if not specified, equals to 3) -- useful, for example, to create 1-star levels like the single choice levels.
  • intro: this is the text displayed in the menu that introduces a level. For example:
intro: |
      The people of Selia Prime are bored with always orbiting between the same planets.  Now they want to resettle on a world that gently tours both the inner and outer solar system at different times of year. High Councilor Zeniak pulls out his cyber binoculars eagerly and awaits a fresh night sky.

The iOS application

The iOS app will power the kiosk. Eventually, games should be broken up and published as their own apps.

The iOS app is a simple container for WKWebView (the component which powers Safari). The data still resides remotely on the server. The container displays the website logged in as the special user "kiosk". No data is retained for this user (although we should definitely record some kind of usage data!), and all missions are available.

The Kiosk dashboard will also have some kind of "slideshow", which will be launched whenever some inactivity time has been reached (say, 1 minute).

Building the iOS app

The app container is built using Apache Cordova.


A web-based platform for interactive, gamified astronomical education






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