Game Physics Engine Development, 2nd Edition

18.4 The Mathematics of Rotation 467

application of the vector pr oduct in 3D, however, is the construction of vectors at

right ang les to one another. Recall that for two vectors, a and b,thevectora × b will

be at right angles to both.

In 2D it is useful to be able to do the same thing—to generate a vector at right

angles to another. In 2D, things are simpler. For any given vector, there will be only

one other direction that is perpendicular. There are an infinite number of vectors in

that direction, however, so we need to choose one. The following code chooses the

vector made by turning the original vector through 90 degrees counterclockwise:

Vector2D ...