TUTORIAL SEVEN
Adding Enemies

All shooters need something to shoot at. In this case we opt for those poor aliens again. They may have come to visit us with a message of peace, but our player is interested only in target practice.

The first step is to load the models for our enemy objects:

rem TUT7A
rem Load models for enemies
EneObj=11
for ene=EneObj to EneObj+4
 load object "models\enemy\H-Alien Psionic-Idle.x",ene
 append object "models\enemy\H-Alien Psionic-Die.x", ene, total object frames(ene)+1
 position object ene,2,2,4
 loop object ene,0,25
next ene

Not forgetting the sounds we will need to give our enemies a realistic presence within the game. With additional use of 3D sounds and a scary alien breathing sound we can create the creepy effect of 'what's just around the corner' for our game:

rem TUT7B
EnemySnd=11 : load 3dsound "sounds\enemy.wav",EnemySnd
EnemygunSnd=12 : load 3dsound "sounds\enemygun.wav",EnemygunSnd
EnemydieSnd=13 : load 3dsound "sounds\enemydie.wav",EnemydieSnd

Now we have loaded our enemy media, we must control them within our game. We must control each enemy, ensuring we can move, rotate, handle gravity and play 3D sound for them:

rem TUT7C
rem Variable for finding closest enemy
cdist#=9999.99

rem Handle enemies within world
for ene=EneObj to EneObj+4

 rem If enemy alive
 if object visible(ene)=1

 rem Kill this enemy
 killenemy=0

 rem Move enemy on a slow curve for appearance of intelligence
 if object angle z(ene)=0
   yrotate object ene,wrapvalue(object angle y(ene)+2)
 endif
 if object angle z(ene)=1
  yrotate object ene,wrapvalue(object angle y(ene)-2)
 endif
 if object angle z(ene)=2
  move object ene,0.05
 else
  move object ene,0.02
 endif

 rem Switch direction of curve based on a random value
 if rnd(200)=1 then zrotate object ene,rnd(1)

 rem Handle gravity for enemy
 position object ene,object position x(ene),object position y(ene)-0.01,object position z(ene)

 rem Work out angle and distance between enemy and player
 dx#=camera position x(0)-object position x(ene)
 dy#=camera position y(0)-object position y(ene)
 dz#=camera position z(0)-object position z(ene)
 dist#=abs(sqrt(abs(dx#*dx#)+abs(dy#*dy#)+abs(dz#*dz#)))
 viewa#=wrapvalue(atanfull(dx#,dz#))
 obja#=wrapvalue(object angle y(ene))
 if viewa#>180 then viewa#=viewa#-360
 if obja#>180 then obja#=obja#-360

 rem Closest enemy emits the enemy sound
 if dist#26+25 and object visible(ene)=1
  killenemy=1
 endif

 if killenemy=1
  set bsp collision off 3+(ene-EneObj)
  hide object ene : dec aliensleft
  killenemy=0
 endif

 rem If enemy alive ENDIF
 endif

next ene

To make sure that our aliens appear creepy, we will constantly play their presence sound effect, and scale the 3D sound listener so you only hear them when they are very close to the player:

rem TUT7D
rem Start the enemy presence sound
loop sound EnemySnd
scale listener 0.1

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