Game Development Reference
In-Depth Information
component is a numeric angle value, but in conversation it is often
referred to in looser terminology. For instance, the vector form of
the scalar example above could be something like
four miles per
hour, heading northwest,
though we would not necessarily be able
to do any calculation with that information until we assigned it a
number.
The Vector3D Class
Among the classes in Flash for handling complex math more effi-
ciently is the Vector3D class. It is the code representation of the
vector concept we learned about earlier. It contains x , y ,and z
values to determine its magnitude, and a fourth value, w ,which
stores information about the vector
'
sdirection,suchasanangle.
We will look at an example shortly where we will use the Vector3D
class to simplify some vector math.
VECTOR VERSUS VECTOR3D
There is another class in Flash known as Vector, which I mentioned in
Chapter 4. It has nothing to do with vectors in physics terms. Rather, it
is a special type of Array that stores only one type of value and uses
less memory than an Array by doing so. For instance, if you used Arrays
of Numbers in previous versions of Flash, you can now use a Vector
instead. It has all the same methods and properties of Arrays but is
faster to navigate and more efficient. The name Vector comes from the
C programming language, but really you can just think of it as a typed
Array.
Displacement
Displacement is most easily thought of as the distance between any
two points in space when connected by a straight line. Though it is
technically a vector, we generally think of displacement in terms of
a scalar. That is to say, we don
'
t usually consider the direction of
one object relative to another when computing their distance apart
from each other. It would be odd to refer to the distance from
one
'
s self to a nearby table as
4ft,30
°
from my facing direction.
We simply say
four feet.
Velocity
Displacement over a period of time results in what we know as
speed . For instance, if it takes me an hour to walk five miles, my
speed is five miles per hour (5 mph). However, as discussed above,
this is merely a scalar value as it has no directional information. If
we add a direction, such as 90
°
,wegetthevectorof velocity .
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