This is the engine room of Shmupkit. The Spawner itself is a blank sprite, and it's event controls which enemies should be spawned, where, how many and sets up all the parameters that control the enemy which are passed to the enemy event.
It's basically a data table of values that are read from whenever the player progresses to a new level/attack wave.
The Spawner makes sure the right sprites, numbers of sprites and delays between sprites are spawned correctly, and ensures there aren't too many sprites on screen at once which could otherwise cause display issues.
EVENT SPRITETYPE7 ; VARIABLES ; ======================================================= ; DIRECTION - availabe for use in your game ; SETTINGA - STATUS: ; 0 = GET DATA FOR NEXT LEVEL ; 1 = SPAWN ALIENS ; SETTINGB - TIMER BETWEEN SPAWNS ; AIRBORNE - SPAWNER MOVEMENT (not implemented yet) ; JUMPSPEED - # OF ENEMIES SPAWNER ; ======================================================== ; ALIEN SPAWNER ; ============ 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 IF SETTINGB = G ; has timer reached the delay point? IF JUMPSPEED < E ; are there still enemies left to spawn? IF S < 9 ; are there 10 or less enemies already on screen? SPAWN J K ; spawn an enemy ADD 1 TO JUMPSPEED ; increment the number spawned SPAWNED ; switch to the enemy sprite LET DIRECTION = 0 ; set its initial direction to 0 ENDSPRITE ; return to the spawner ENDIF ELSE ; all enemies in this level have been spawned IF F = 0 ADD 1 TO L ; get ready for next level IF L = 13 ; have we reached the end of the levels? LET L = 1 ; yes, start again ENDIF LET SETTINGA = 0 ; get data for next level ENDIF ENDIF LET SETTINGB = 0 ; reset the timer ENDIF ADD 1 TO SETTINGB ; increment the timer ; Alien Spawner 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 DATA 0 232 16 5 2 12 6 15 69 1 8 100 100 DATA 0 8 32 5 2 6 6 15 70 1 8 100 8 DATA 0 232 146 5 2 6 6 20 71 1 4 100 8 DATA 0 8 146 5 2 6 6 20 66 1 4 100 8 DATA 0 40 8 5 2 6 8 5 69 1 2 140 8 DATA 0 200 8 5 2 6 8 5 69 1 2 140 8 DATA 0 200 8 5 2 6 8 5 69 1 2 140 8 DATA 0 8 128 5 2 6 8 5 67 1 10 100 8 DATA 0 80 8 5 2 6 8 5 67 1 10 100 8 DATA 0 80 8 5 2 6 8 5 67 1 10 100 8