AS3 enemy formations - actionscript-3

Question

I have been developing a shooter game in as3 using the starling framework by looking at some different tutorials.
The problem is that all tutorials teach to create random enemies that move from one side to other. I want to know how can I create different formations of enemies on screen.
Can anyone suggest any books, tutorials, or any basic algorithm to put me on track?

Answer 1

Here is a rather simple way to spawn a formation.
Create a symbol in your library called formation and use that as your linkage/class name as well.
In that symbol place 5 marker MovieClips at whatever locations you want. For the marker clip I recommend using a circle that is centered. Wherever you place those markers, represents where the enemies will be spawned.
Now, in your code where you want to spawn this formation, you can do this :
var formationData:MovieClip = new formation;
for (var index:int = 0;index < formationData.numChildren;index++)
{
var spawnMarker:MovieClip = formationData.getChildAt(index) as MovieClip;
var enemy:Enemy = new Enemy;
enemy.x = spawnMarker.x;
enemy.y = spawnMarker.y;
addChild(enemy);
}
Now, that will spawn a formation based on what you set up in your formation symbol.
You can offset the location of your enemies that get spawned by doing something like this :
var offsetX:Number = 200;
var offsetY:Number = 50;
for (var index:int = 0;index < formationData.numChildren;index++)
{
var spawnMarker:MovieClip = formationData.getChildAt(index) as MovieClip;
var enemy:Enemy = new Enemy;
enemy.x = offsetX + spawnMarker.x;
enemy.y = offsetY + spawnMarker.y;
addChild(enemy);
}
What this concept allows you to do, is visually layout your formations in the flash IDE. So you could create a whole bunch of different formations and choose a random one. Have the spawn points spell out a word ?
Obviously the code above is an example, you would need to integrate the concept into your spawn system etc.
Depending on where your enemies are spawning from, you might need to use the offset to start them offscreen.