HTML and CSS Reference
Step 5: Add Vlad Vukićević's WebGL helpers for rotation.
that “these routines were borrowed from a sample previously written by Vlad Vukićević,”
whose blog you can find at http://blog.vlad1.com . Vlad has created a couple of tools to help
with rotation and with pushing and popping data. Append his rotation logic to gd.core
with the following code.