Flash MX 2004 Games : Art to ActionScript

Flash MX 2004 Games
the distance between two locations. Finally we convert the ‘point’ into a string using the ‘dump’
function defined in lines 16 to 18.
1 class point{
2 var x:Number = 0;
3 var y:Number = 0;
4
5 function point(xx:Number, yy:Number){
6 x = xx;
7 y = yy;
8 }
9
10 function distanceTo(pt:point):Number{
11 var dx:Number = x - pt.x;
12 var dy:Number = y - pt.y;
13 return Math.sqrt(dx * dx + dy * dy);
14 }
15
16 function dump(){
17 return ("(" + x + ", " + y + ")");
18 }
19 }
Listing 10.2
Listing 10.3 shows how we use the ‘point’ class. Line 1 creates a new point with the x value
set to 10 and the y value set to 10. By using the new keyword Flash knows to try to find a class
definition of point in the current folder. It finds the definition in the ActionScript file ‘point.as’.
Flash then looks in the class for the constructor function, simply a function with the same name
as the class, and uses the parameters passed to initialize the class. Lines 3 and 4 show how the
output from the ‘dump’ function can be used within a ‘trace’ statement and the output from the
‘distanceTo’ is also used.
1 pt1 = new point(10, 10);
2 pt2 = new point(100, 50);
3 trace("Distance from " + pt1.dump() + " to " +
4 pt2.dump() + " is " + pt1.distanceTo(pt2));
Listing 10.3
In a complex project there could be several programmers working on different ActionScript
class files. Another very useful feature of classes is their ability to inherit the characteristics of an
existing class. Listing 10.4 shows the ‘vector’ class. A vector has the same data set as a point; namely,
in the case of a two-dimensional vector, it has just two numeric values, but instead of representing
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