Building the Flak Cannon Game Loop - The Essential Guide to Flash Games - page 202

We are finished with the checkCollisions() function, but we still need to create a few functions to
support the code we just added. The first function is createExplosions() . This function accepts
the (x,y) coordinates to place an instance of the Explosion object. Recall the Explosion class that
we created in Chapter 4. It displays multiple frames of animation to simulate an explosion.
Creating the explosion and putting it on the screen is a very straightforward operation. We have
used similar code several times previously in Flak Cannon. Here is the full code for the function.
private function makeExplosion(explodeX:int,explodeY:int):void{
tempExplode = new Explosion();
tempExplode.x = explodeX;
tempExplode.y = explodeY;
this.addChild(tempExplode);
explodeArray.push(tempExplode);
}
The addToScore() function is called whenever the player gains points by destroying Enemy planes.
addToScore() accepts the value to add to the player's score as its only parameter. The score is
updated, and an event is dispatched to tell the ScoreBoard to display a new score value. We also
call checkBonusShips() . This function, described a bit further on in this chapter is used to check to
see if the player has attained a score that will net an extra Ship for the fleet.
private function addToScore(val:Number):void {
score += int(val);
checkBonusShips();
dispatchEvent(new CustomEventScoreBoardUpdate(
CustomEventScoreBoardUpdate.UPDATE_TEXT,Main.SCORE_BOARD_SCORE,String(score)));
}
The checkBonusShips() function does a simple arithmetic test to see if the player has attained a
score that will award an extra Ship . However, there is a trick to it that may not seem evident at
first. We have created a difficulty setting named scoreNeededForExtraShip . For this game,
scoreNeededForExtraShip is 10000 , but it could be any score. It might seem logical that we would
simply check to see if the player's score is equal to some multiple of scoreNeededForExtraShip
(e.g., 10000 , 20000 , and 30000 ), and if so, award an extra Ship . However, we cannot be sure that
the player's score will ever actually be equal to multiple of scoreNeededForExtraShip , so there is
a good chance we will never award the player an extra Ship if we simply look at this value.
Alternatively, if we look for a score that is greater-than-or-equal-to scoreNeededForExtraShip , we
will continue to award the player an extra Ship every time we call this function, after the first
multiple of scoreNeededForExtraShip is reached. Instead, we must use a combination of both
checks to award the proper amount of bonus Ship objects to the player. Here is the calculation:
if ( (score-(extraShipCount*scoreNeededForExtraShip) >= scoreNeededForExtraShip) ) {
For this example, let's pretend the player has a score of 20,100 and has earned one bonus ship
already in the game. Here it is translated into a more readable form:
If 20100-(1*10000) >= 10000
We could write this even more simply as follows:
If 10100 >= 10000
Since this statement is true, the player gets an extra Ship . However, the next time this calculation
is called, called it would be like so:
If 20100-(2*10000) >= 10000