Vertical Shmup - Part 6 - Killing Aliens

The basic game mechanics have started to take shape so now we'll tackle killing the aliens, first, we'll create a new Sprite for enemy explosions, something like this:

Next, we'll write some code for the Explosion, I'm going to use Sprite Type 6 for explosions:

EVENT SPRITETYPE6
 
 
 ANIMATE ; regular amination
 IF FRAME = 4 ; are we on the last frame?
  IF DIRECTION = 0 ; was enemy hit by a torpedo?
  REMOVE ; yes, remove this sprite
  SUBTRACT 1 FROM S ; decrement the sprite counter
  ENDIF
 ENDIF

This will remove the explosion once it reaches the last frame, and reduce the number of on screen sprites.

Now, we'll add in some collision detection code into to our Alien sprite event (type 2) Add the code below to the bottom of your Sprite Type 2 event:

; COLLISIONS
  ; ===================
 IF COLLISION 1 ; if hit by a torpedo
  OTHER ; switch to the torpedo
  IF DIRECTION = 1 ; is it unexploded?
  LET DIRECTION = 99 ; explode the torpedo
  ENDIF
  ENDSPRITE ; return to this sprite
  LET TYPE = 6 ; switch it to the explosion type
  LET IMAGE = 4 ; and the explosion image
  LET FRAME = 0 ; reset it to first frame
  LET DIRECTION = 0 ; this is an alien exploding
 ENDIF
 
 

This does two things when a collision between a torpedo and an Alien is registered:

1) it tells the torpedo to explode

2) it switches the Alien to the Alien Explosion Type and Image

Let's build and test:

{insert video}

Cool, now we can shoot them!

Although, I can see one obvious flaw, notice how nothing happens when our player spaceship collides with an Alien, we need to fix that so both the Alien and the Player explode.

Head back to your Alien Event (type 2) and add the following code to the bottom:

 IF COLLISION 0 ; if enemy and player collide
  LET TYPE = 6 ; switch it to the explosion type
  LET IMAGE = 4 ; and the explosion image
  LET FRAME = 0 ; reset it to first frame
  LET DIRECTION = 0 ; this is an alen exploding
  OTHER
  LET TYPE = 6 ; switch it to the explosion type
  LET IMAGE = 4 ; and the explosion image
  LET FRAME = 0 ; reset it to first frame
  LET DIRECTION = 1 ; this is the player exploding
  ENDSPRITE
 ENDIF
 

Now both will explode when the two ships collide.

We're making some decent progress here, but there's still lots to do, however, before I go any further I think we've got a gameplay decision to make.

NEXT: Part 7 : A Gameplay Decision