Building the Flak Cannon Game Loop - The Essential Guide to Flash Games - page 200

bonusplane: for (ctr2 = bonusPlaneLength; ctr2 >= 0; ctr2--) {
tempBonusPlane = bonusPlaneArray[ctr2];
var bonusPlanePoint:Point = new Point(tempBonusPlane.x, tempBonusPlane.y);
for (ctr = flakLength; ctr >= 0; ctr--) {
tempFlak = flakArray[ctr];
flakPoint = new Point(tempFlak.x, tempFlak.y);
if (tempFlak.image.bitmapData.hitTest(flakPoint,255,

tempBonusPlane.image.bitmapData,bonusPlanePoint)) {
dispatchEvent( new CustomEventSound(CustomEventSound.PLAY_SOUND,

Main.SOUND_BONUS,false,1,0,1));
shots += tempBonusPlane.bonusValue;
dispatchEvent(new CustomEventScoreBoardUpdate(

CustomEventScoreBoardUpdate.UPDATE_TEXT,Main.SCORE_BOARD_SHOTS,

String(shots)));
makeExplosion(tempBonusPlane.x + tempBonusPlane.width/2,

tempBonusPlane.y + tempBonusPlane.height/2);
addToScore(baseBonusPlaneScore+(tempFlak.hits*enemyHitBonus));
tempFlak.hits++;
removeItemFromArray(tempBonusPlane,bonusPlaneArray);
break bonusplane;
}
}
}

By the way, we could have made the bonus planes a special case Enemy object, instead of its
own type. In that case, we would have only had to do the loop once. Finding ways to optimize the
code beyond what is presented in this text is a good way to further hone your game development
skills.
Now, we have to test the player's ships against the Enemy planes. Unfortunately, we have to loop
through the enemyArray arrays again. Fortunately, we do this for a good reason. Since the Ship
objects always sit at the same y coordinate on the screen, we can do a quick test to see if we
have to do collision detection based on the current y location of an Enemy .
Notice the ship : that precedes the for loop. This is another label. Again, we will use this label to
break out of a loop if the item we are testing has been removed from the array. Most of the rest of
this should look familiar to you by now.
ship: for (ctr = shipLength; ctr >= 0; ctr--) {
tempShip = shipArray[ctr];
var sPoint:Point = new Point(tempShip.x, tempShip.y);
enemyLength = enemyArray.length-1;
for (ctr2 = enemyLength; ctr2 >= 0; ctr2--) {
tempEnemy = enemyArray[ctr2];
Here is where this loop gets interesting. We will test to see if the current y position of the Enemy is
close enough to the Ship objects for a collision to occur. Since the Ship objects are always in the
same place, all we have to do is calculate the first point at which an Enemy could possible hit a
Ship . Otherwise, we skip the test. To do this, we will take the gameHeight and subtract the height
of a Ship plus subtract shipYPadding pixels (because Ship s are shipYPadding pixels from the
bottom of the screen). Then, we subtract the height of the Enemy plane because its registration
point is in the upper-left hand corner. Figure 5-10 shows how we came to this calculation.