HTML and CSS Reference

In-Depth Information

Moving in a Simple Spiral

There are many complicated ways to move an object on a spiral path. One such way would

be to use the Fibonacci sequence, which describes a pattern seen in nature that appears to cre-

ate perfect spirals. The Fibonacci sequence starts with the number 0, and continues with each

subsequent number calculated as the sum of the two previous numbers in the sequence. Each

subsequent rotation of the spiral is the sum of the two previous numbers (1, 2, 3, 5, 8, 13, 21,

34, 55, 89...). However, as you might imagine, the math used to create this sequence is quite

involved, and it is also difficult to translate to object movement.

For our purposes, we can create a simple spiral by increasing the radius of the circle path on

usInc
variable, which we will use as the value to add the radius movement path of the circle.

We create this new variable in
canvasApp()
:

var

var
radiusInc
=
2
;

Then, in
drawScreen()
, we add the following code to increase the radius of the circle every

time we move the object:

circle
.
radius
+=
radiusInc
;

In
Figure 5-14
,
you can see what the resulting spiral looks like. (To illustrate the path, this ex-

ample includes the points.)

Ifyouwant a tighter spiral, decrease the value of
radiusInc
.Conversely,if youwant a wider

spiral, increase the value of
radiusInc
.

Example 5-10
shows the code for
CH5EX10.html
from the code distribution.