Building the Flak Cannon Game Loop - The Essential Guide to Flash Games - page 193

Shooting the BonusPlane awards the player 10 shots for the Flak cannon (note that the
number of shots could be made into a difficulty setting).
There can only ever be as many BonusPlane objects as set in the maxBonusPlanes
setting.
Besides these rules, checkBonusPlane() acts a lot like CheckEnemies() . First of all, we will use a
difficulty setting named bonusPlaneDelay . This setting tells us how long the game should wait
before a BonusPlane arrives. We do not want it to come too early or too often, or the player will
have an unfair advantage against the Enemy planes. The delay is calculated in frames. We use
bonusPlaneFrameCounter to keep track of how frames have passed between BonusPlane arrivals.
private function checkBonusPlane():void {
bonusPlaneFrameCounter++;
if ( bonusPlaneFrameCounter >= bonusPlaneDelay) {
if (bonusPlaneArray.length < maxBonusPlanes) {
Now, we get to create an instance of BonusPlane . The first thing we will do is set the starting y
value for the plane. For this, we will simply get a random number between 0 and bonusPlaneMaxY .
This difficulty setting represents the highest y value (lowest place on the screen) that a
BonusPlane can fly. The starting x value is -32 , which means it will always start off the right side of
the screen, just far enough so the entire image is not visible. The ending x value is gameWidth+32 ,
wihich means the plane will fly until it is entirely off the right side of the screen. Both the starting
and ending y values are set to randomY because the y value will never change as the plane flies
acrosss the screen.
var randomY:int = Math.floor(Math.random()*bonusPlaneMaxY);
We also need to set the speed of the BonusPlane . The speed of the plane will increase on every
level. However, we do not want the plane to get too fast, or the player will not be able to shoot it
down. Because of this, we use the bonusPlaneSpeedMax difficulty setting. If the BonusPlane speed
is too fast, our code will set it to the maximum value.
The only thing left is to create an instance of BonusPlane and push it into bonusPlaneArray . Recall
that we give the player ten extra shots when a BonusPlane is shot down. The last parameter in the
call to BonusPlane is the literal 10 , which represents this value. The BonusPlane could support
different values for this bonus, but we are going to make it 10 every time. We then add it to the
display list with addChild() and reset the bonusPlaneFrameCounter so we can test for another
BonusPlane when the proper number of frames have passed.
tempBonusPlane =new BonusPlane(-32,randomY,gameWidth+32,randomY,bonusPlaneSpeed,10);
bonusPlaneArray.push(tempBonusPlane)
this.addChild(tempBonusPlane);
} else {
bonusPlaneFrameCounter = 0;
}
}
}