If you recall, when we gave the Aliens the ability to fire missiles, one of tests that the code performs is to see if the Alien is positioned in the range 8pixels either side of the player - this seems a bit restrictive to me, so let's add a new Variable to the Spawner event (TYPE 7) which will allow us to define the distance either side of the player that an alien needs to be in to be allowed the chance of firing their missile.
We'll add in variable I to the list of values we'll read in
IF SETTINGA = 0 ; first time we run this LET JUMPSPEED = 0 ; reset the enemies spawned counter LET SETTINGB = 0 ; reset the timer RESTORE ; start from the beginning of the data table REPEAT L ; get the data for this level READ AIRBORNE ; get the spawner movement READ X ; get starting x position READ Y ; get starting y position READ J ; get the enemy sprite type READ K ; get the enemy image READ E ; how many enemies in this level? READ G ; delay between releasing each enemy READ P ; points for a kill READ C ; colour READ W ; weapon READ H ; fire weapon probability READ Q ; min height to release weapons READ I ; x distance for alien weapon triggering ENDREPEAT LET D = E ; how many kills to get bonus? LET F = E ; enemies remaining ADD 1 TO SETTINGA ; prevent this running again ENDIF
Then make sure to add a new value to the end of each row in your data table:
DATA 0 132 8 5 2 8 8 5 67 1 10 100 8 DATA 0 100 8 5 2 10 8 10 68 1 10 100 32
By altering these values you can make the aliens fire when further horizontally away from the player (or when nearer)
Next, there's some code in the Alien event (Type 5) that is repetitive, we could save a few bytes by optimising it, specifically the test to see if the player is out of bounds:
We could optimise this by using the DIRECTION variable, setting it to 254 whenever an enemy leaves the screen:
So, we will change this:
; BOUNDARY CHECKING ; =================== IF X <= LEFTEDGE ; if alien reaches the left edge REMOVE ; remove it SUBTRACT 1 FROM S ; decrement the sprite counter SUBTRACT 1 FROM F ; decrement the number of aliens still in ENDIF IF X >= RIGHTEDGE ; if alien reaches the right edge REMOVE ; remove it SUBTRACT 1 FROM S ; decrement the sprite counter SUBTRACT 1 FROM F ; decrement the number of aliens still in ENDIF IF Y >= BOTTOMEDGE ; if alien reaches the right edge REMOVE ; remove it SUBTRACT 1 FROM S ; decrement the sprite counter SUBTRACT 1 FROM F ; decrement the number of aliens still in ENDIF
to this:
; BOUNDARY CHECKING ; =================== IF X <= LEFTEDGE ; if alien reaches the left edge LET DIRECTION = 254 ; enemy is out of bounds ENDIF IF X >= RIGHTEDGE ; if alien reaches the right edge LET DIRECTION = 254 ; enemy is out of bounds ENDIF IF Y >= BOTTOMEDGE ; if alien reaches the right edge LET DIRECTION = 254 ; enemy is out of bounds ENDIF IF DIRECTION =254 ; is enemy out of bounds? REMOVE ; remove it SUBTRACT 1 FROM S ; decrement the sprite counter SUBTRACT 1 FROM F ; decrement the alien counter ENDIF
That should save us a few bytes, plus makes it easy if we want to remove a sprite (but not kill it) in other parts of the game.
And that, I think, should wrap it all up for now and give you a lightweight (currently uses approx 14,500 bytes) framework for building Shoot em ups in MPAGD.
I'm off o tidy up the comments in the code then I'll release the whole project on the itch website so you can get started quickly!