Some lessons in WebGL

This repository contains a series of simple lessons in WebGL, plus some related examples.

The folders named lesson01, lesson02, and so on are a sequential tutorial and are best understood using the explanatory text.

The form of the first ten lessons is very loosely based on NeHe Productions' well-known OpenGL tutorial, which can be found here.

The lessons from 11 onwards are not related to the NeHe ones.

The folders named example01 etc are example code for interesting stuff outside the scope of the tutorial, and have their own README.txt files with details.

Problems seeing the lessons?

When experimenting with the lessons later than #5 you may encounter errors resulting from "cross-origin" file access. This is caused by the browsers' security systems:

• Browsers want to stop pages from one server ("origin") from gaining access to data from another origin except under closely-controlled circumstances. (For example, imagine if a hostile website tried to gain access to data from the online banking window you had open in another tab.)
• Unfortunately, when files are loaded from the filesystem, the browser sees each file as a separate origin. So when one of these examples tries to load, say, a texture to display on a cube, it will fail.

There are two ways you can work around this. The best, safest way is to use a local webserver, but an alternative if you're careful about it is to temporarily disable the cross-origin restrictions.

The dangerous way

Switch off the same-origin policy. This is perfectly safe if you're only going to use the browser for testing your own code, but isn't a good idea in general (it's all too easy to casually browse over to an internet site without thinking about it). Still, if you want to do this:

• Firefox: set the security.fileuri.strict_origin_policy setting in about: config to "false".

• Chrome: use the the --allow-file-access-from-files and --disable-web-security switches command-line options (ideally just the first). If you're using a Mac, Stuart Carnie has written a convenient application bundle for this here: http://aussiebloke.blogspot.com/2011/08/local-file-system-development-with.html

The safe way #1

Run a Ruby/Python/Perl etc server directly in the folder

• cd webgl-lessons
• Run any of the one-liners from this gist depending on what you have installed on your machine

The safe way #2

Run a local web server to host these lessons using Apache under Mac OS X; GNU/Linux will be similar. If you're on Windows, check out Xampp.

1. Add an entry for webgl-lessons.local in /etc/hosts.

This will need to be done as the root user using your preferred editor:

$ sudo <editor> /etc/hosts

Add the following line and save the file:

127.0.0.1       webgl-lessons.local

Tell the operating system to flush and reload the local DNS cache:

dscacheutil -flushcache

Test to see if http://webgl-lessons.local/ is working:

$ dscacheutil -q host -a name http://webgl-lessons.local/
name: http://webgl-lessons.local/
ip_address: <ip_address>

2. Add an Apache vhost configuration:

This will need to be done as the root user using your preferred editor:

$ sudo <editor> /private/etc/apache2/extra/httpd-vhosts.conf

Add the following vhost configuration replacing with the actual path on your filesystem:

<VirtualHost webgl-lessons.local:80>
   ServerName webgl-lessons
   DocumentRoot <path-to-webgl-lessons>/
   <Directory <path-to-webgl-lessons>>
     Options +Indexes +FollowSymLinks +MultiViews +Includes
     AllowOverride All
     Order allow,deny
     Allow from all
     DirectoryIndex index.html
  </Directory>
</VirtualHost>

After making the change in the Apache vhost configuration first confirm the syntax for the Apache configuration is still correct:

$ apachectl configtest
Syntax OK

If the syntax is OK then restart Apache:

$ sudo apachectl restart

Now you can open the webgl-lessons in any local browser at this url: http://webgl-lessons.local/