Building the Flak Cannon Game Loop - The Essential Guide to Flash Games - page 189

Checking for enemies
The first thing we do in our runGame() function is call checkEnemies() . This function is designed to
work with the enemyWaveDelay difficulty setting and the enemyFrameCounter variable. Its job is to
test to see if a new enemy plane should be created to attack the player's fleet.
The first few lines of code set up the function and then test to see if we need to create an enemy.
First, we increment enemyFrameCounter and test it against enemyWaveDelay . On the first level,
enemyWaveDelay is set to 60 . That means that 60 frames need to fire before an enemy is created.
We also test incomingCount against numEnemies . incomingCount is incremented each time an
enemy is created. numEnemies is another difficulty settings that represents the number of enemies
per level. On the first level, this is set to 15 .
private function checkEnemies():void {
enemyFrameCounter++;
if ((enemyFrameCounter >= enemyWaveDelay) && (incomingCount < numEnemies)) {
Now, we need to test to see if we are going to create a wave of multiple enemies, and if so, how
many enemies we will create. For this, we will test the enemyWaveMultipleChance difficulty setting
against a percentage chance random number (1-100). If the random number ( chance ) is less
than or equal to enemyWaveMultipleChnace , the current wave we are creating will have multiple
enemies at the same time. The more enemy planes that arrive at the same time, the harder it will
be for the player to shoot them all down.
var chance:int = Math.floor(Math.random() * 100)+1;
var enemiesToCreate:int = 1;
Figure 5-4 shows what the screen will look like when Enemy planes start appearing in timed
intervals.
Figure 5-4. Single enemies flying down
If we do have multiple enemies, as shown in Figure 5-5, we will then find out how many by
creating a random number with the maximum value using another difficulty setting, enemyWaveMax .
We place that value into the local enemiesToCreate variable.