Trigonometric Identities (Razones Trigonométricas)

Basically, if you study computer graphics you need to know some basic trigonometric identities, in order to understand some results, like 2D or 3D rotations. Here I provide a couple of links to lists of trigonometric identities:

• http://www.ucm.es/info/Geofis/practicas/trigonometria.htm
  
• http://www.sosmath.com/trig/Trig5/trig5/trig5.html
  
• http://en.wikipedia.org/wiki/Trigonometric_identity
  

And the most basic application, 2D rotation:

• Siggraph 2D rotation

If you can read Spanish I´ll recommend you to check this slides from the "Computer Graphics Fundamentals" course of the University Of Las Palmas de Gran Canaria.

Friend Classes (strange justification)

I'm not a friend of the C++ friends, whether they are functions, member functions or classes. However there are some situations when the use of a friend function can be somehow beneficial, like making the operator << compatible with a particular class (although it's possible to just override or create a kind of toString() method, like in the best Java flavour).

Lately I've been reading a book on C++ programming. This book is intended to be read by novices, and because of that I think the author should have been more careful when giving advices. This is the way the author justifies friend classes:

"When might you want to make one class a friend to another? Let’s look at an example. Suppose you must program a simple simulation of a television and a remote control. You decide to define a Tv class representing a television and a Remote class representing a remote control. Clearly, there should be some sort of relationship between these classes, but what kind? A remote control is not a television and vice versa, so the is-a relationship of public inheritance doesn’t apply. Nor is either a component of the other, so the has-a relationship of containment or of private or protected inheritance doesn’t apply. What is true is that a remote control can modify the state of a television, and this suggests making the Remote class a friend to the Tv class."

This is exactly the example my teachers at university used to teach as an event broadcast pattern like Observer, which is by far a better solution.

Friend classes completely break encapsulation, and couples classes so tight that it will be impossible to use one without the other, therefore preventing code reuse.

The book is called "C++ Primer Plus, Fifth Edition".

Programming cheat sheets

Either if you are a novice or an experience programmer it's always a good idea to have at hand one cheat sheet that helps  you not to make the most usual syntax mistakes. Here you have a compilation of different programing languages' cheat sheets:

Programming Cheat Sheets (www.cheat-sheets.org)

Enjoy!