3D Game Programming

What happens without the parentheses? Can you guess why?^1

Geometry

We’re working on 3D game concepts in this book, which means geometry.

We’ll discuss geometry in more detail as part of the various project chapters

that need it. For now let’s consider two geometric functions: sine and cosine.

If you don’t know them, don’t worry—you’ll get to know them in the games.

Just remember that in JavaScript, we do not use degrees. Instead we use

radians. What are radians? Instead of saying that we turned 180° when we

spin half way around a circle, we would say that we turned pi radians around.

Pi is a special number in math. Its value is about 3.14159. You will often see

the symbol π used for pi. We’ll call it pi since JavaScript calls it Math.PI.

Going around a full circle is twice as much as 180° turn—more commonly

called a 360° turn, this is two pi radians, or 2 × pi.

By the way, 2 × pi is the 6.3 that we said was a full rotation way back when

we first started talking about rotation in Making Boxes with the Cube Shape,

on page 6. Since the number value of pi is about 3.15, then 2 × pi is 2 × 3.15,

or 6.3.

1. Without parentheses, multiplication is done first, then division. Remember the “order
   of operations” from your math class!

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Changing Things • 71

Prepared exclusively for Michael Powell