[JAVA][Beginning Java 8 Games Development]

Chapter 17 ■ Enhancing Game Play: Creating a Scoring Engine, Adding Treasure and an Enemy Auto-Attack Engine
Once your conditional if() timer logic has expired (completed its countdown), your Enemy sprite is randomly
positioned along the Y axis, moved into its starting position using the spriteMoveR and spriteMoveL variables, and the
attackCounter is reset to zero for the next time the callAttack variable is set to false. At the end of the “set-up initiate
attack” sequence of Java statements, callAttack is set equal to true, as seen in Figure 17-36, using the following code:
public void update() {
if(!callAttack) {
if(attackCounter >= attackFrequency) {
attackCounter = 0;
spriteFrame.setTranslateY(randomNum.nextInt(attackBoundary));
spriteMoveR = 700;
spriteMoveL = -70;
callAttack = true;
} else { attackCounter+=1; }
} else { initiateAttack(); }
}
Next we’re going to rewrite our if(takeSides) logic structure to remove the Y axis random number positioning
statements, reposition the takeSides boolean flag program logic, and add an if(!onScreen) nested structure, around a
.setTranslateX() method call. This will allow us to animate the iBeagle Enemy Actor sprite on and off of the screen.
Inside of the if(!takeSides) structure, you’ll keep the first two statements that set the sprite mirroring (facing
direction), but remove the .setTranslateY() method call as that is now accomplished in the .update() method. Add the
if(!onScreen) conditional structure, where you’ll initialize the destination location to 500 pixels, and then nest another
counter if(spriteMoveR >= destination) structure, inside of which you’ll move the sprite by two pixels per pulse
using spriteMoveR-=2; in conjunction with spriteFrame.setTranslateX(spriteMoveR); to actually move the sprite
as the counter changes, thus leveraging the counter variable in the sprite animation (movement) logic.
The else part of the if-else structure will (eventually) shoot the projectile using a .shootProjectile() method we
will be coding soon, and since the sprite is now on the screen, we will set the onScreen boolean flag variable to a true
value, which, for now, will trigger the second if(onScreen) conditional logic structure. This will remove the Enemy
sprite from the screen using half the velocity (move one pixel per counter iteration) that it came onto the screen with.
The logic for the second nested conditional if(onScreen) structure is quite similar to the first. You will set the
destination to 700 pixels (putting the Enemy sprite back off-screen, and again out of view), and this time, you’ll
iterate using +=1 instead of -=2, which will not only move the Enemy in the opposite direction, due to a plus instead
of minus, but will also use half the initial velocity used to mount an attack, because you’re moving by one pixel rather
than two.
The real difference in the if(onScreen) conditional if-else structure is in the else portion of the programming
logic, where we not only set the onScreen boolean flag variable back to false, but we’ll also set the takeSides boolean
variable to true, so that the Enemy will use the other side of the screen for his next attack attempt.
Finally, since the attack sequence is completed, we will also set the callAttack boolean flag variable to false. As
you know, this will start up the attackCounter program logic in the .update() method, which will give your player a few
seconds to recover from being attacked. The Java structure for the entire if(!takeSides) conditional structure, and its
nested if(onScreen) conditional structures, is shown highlighted in Figure 17-37, and should look like the following:
private void initiateAttack() {
if(!takeSides) {
spriteFrame.setScaleX(1);
this.setIsFlipH(false);
if(!onScreen) {
destination = 500;
if(spriteMoveR >= destination) {
spriteMoveR-=2;
spriteFrame.setTranslateX(spriteMoveR);
426
www.it-ebooks.info